Trying to emulate three synchros using Arduino - Page 1
Forum section: electronics / projects

author: richfiles
author_rank: Regular Contributor
timestamp: July 20, 2015, 07:56:40 pm
content: I'm trying to emulate three synchros using Arduino. A synchro is a type of rotary transformer that takes an AC input and generates three amplitude adjusted outputs that represent the angle of the rotor. It looks a lot like a three phase motor winding. My application is to drive this: A 3 axis FDAI (Flight Director/Attitude Indicator).•••• EDIT ••••(Dec-2021)I have found the following parts that will most likely be used:• California Instruments 850T Precision Oscillator (salvaged from equipment from previous employer. This is my 400 Hz Sine source.)• MCP4922 12-bit Dual DAC with Voltage Reference (5 on hand - Supports multiplying functionality)• 74HC4066 Quad Bilateral Analog Switch (90 on hand - I might have enough)• TA8251AH 4ch x 18W Audio Amplifier (I have a whole tube of these. Might use 'em, might not)• LM675 Power Op-Amp (16 on hand... And I don't trust a single one of these. Possibly counterfeits. Dang it China...)To reiterate, because it gets missed,a lot,the design I've chosen uses a hardware sine wave generator (California Instruments 850T Precision Oscillator) to generate the 400 Hz sine wave, uses a set of analog switch chips to select whether to use an inverted or a non-inverted sine wave, and feeds that into the voltage reference of a multiplying DAC. The microcontroller only needs to update the attenuation values of the DAC, and the sine wave is attenuated entirely by the hardware.I will NOT in any way, shape, or form, be generating the sine waves from the microcontroller. There is no need. It doesn't need to be suggested. It keeps getting brought up. Enough that I'm going through old posts to strike-through older speculative info that's no longer relevant.Finally,a 115vac 400Hz Power Amplifier has been developed!Special thanks to random internet denizen "Dr. Rockzo" for his crucial aid developing a viable power amplifier capable of taking the precision reference sine wave as an input, and driving the 115vac 400Hz output needed to supply the ADI with power while also retaining the precision required as a reference. I have created a new thread detailing the development of the Power Amplifier circuit, which can be found here:https://www.eevblog.com/forum/projects/28vac-115vac-inverter-that-can-be-driven-by-400hz-analog-sine-wave/•••• END EDIT ••••My goal is to use the Kerbal Space Program SerialIO mod that outputs the game's vessel telemetry to an arduino over USB. I have a nice big pile of meters, switches, and other goodies, but the FDAI is my prize collection piece! Almost no one has done a physical "navball" in Kerbal Space Program. I know that these are very commonly installed in flight simulators. That's actually where mine came from, in fact. A lot of flight sims only use a 2 axis model. 3 axis models are more frequently used in fighter jets, stunt planes, and space craft.These devices take a reference 115 volt ac, 400 Hz signal for both power and as the reference. Each of the three axes have three inputs that come from the synchros on the gyro gimbals. When the synchro transmitter transformer sends the 400 Hz ac sine wave over the three wires, it represents the angular magnetic alignment of the rotor. Inside the FDAI, three synchro receivers output the null error from their rotor, which feeds into a servo amplifier that drives a servo paired to each synchro receiver to zero out the error.Anyway,I'm uncertain if the arduino has the beefiness to pull this off entirely in software emulation. Maybe it does, maybe it doesn't.I'm only just beginning... as in I'm still investigating and studying. I've not coded anything yet. Since I need to drive the reference output at 115 vac 400 Hz, and the synchro outputs at 28 vac 400 Hz, I figure it pays to rely on some support hardware to lighten the Arduino's load anyway.I'm thinking I could buy a MAX038 off ebay to generate a nice clean 400 Hz sine wave, and go withdigital potentiometers to set the 9 amplitude modulated outputs. The only question I have, is that digital pots seem to come mostly in 256 step (8 bit) varieties, and some 10 bit, 1024 step versions are out there.I need to be able to represent 360 degrees of rotation, and I'd like to avoid a jumpy ball, so I won't even consider the 256 step d-pots. I still wonder if the 1024 step d-pots are enough. The amplitudes I need to represent swing fully positive and negative, and the rate of the swing conforms to the curve of a sine wave, represented by the phase angle of the particular winding vs the rotor. Basically, I do not believe it's linear by a long shot. That more or less means I have to waste steps on the low end, and get lots of fine steps (of fudge it) at the top end. I don't think I'll get the full 1024 steps worth of resolution once the math calculates the amplitude of each sine wave output. mirrored against opposing actions on the other two signal lines, I can get half of 360 degrees (180 + or - degrees, with the + or - representing either a rise or a fall in the wave in relation to the angle of the other two). Between step 1023 and 1022, is 3.58157°, yet between steps 512 and 511 (the mid way point if you consider the center step being 0 volts), there is a change of only 0.11190589°. Not sure how that poor resolution near the peak amplitudes will affect things. There will always be two other amplitudes that are not at peak, in the opposite polarity, when one output reaches that low resolution peak.Does anyone know of any 12 bit digital pots? I imagine that would give me great resolution for my application, even at those pesky peak amplitudes.Also, to clarify, there is NOT a phaseshifthappening between phases... The amplitude is modulatedin phasewith the reference, but the angular difference (0°, 120° and 240° windings) cause the sine wave to be attenuated by the sinusoidal angle of the "misalignment" of the rotor's magnetic field angle with the stator's angular orientation relative to the rotor. Clear as mud, right!I've seen a design that pairs two 8 bit digital pots together using three op-amps, but that takes me from 6 support chips (assuming at least dual d-pots) plus output drivers to 13 support chips plus output drivers. It more than doubles what I end up having to build! If I can just find 12 bit or higher digital pots, that'd be ideal. Even if I could only get single pots, it's still better than the other method, as it would only require 10 chips in single pot configuration (or still 6 if I can find dual d-pots). The BIG difference, is it simplifies the programming to not have to juggle values calculated and sent out to two chips to represent one number.Can anyone recommendany higher resolution digital pots, or an alternative part. I need to be able to feed it a sine wave and attenuate it...And dang it... I just added a few op amps, cause I need to attenuate high impedance "copies" of the sine wave... x9.Finally, I was thinking of driving the output with the rails at +/-11.5 volts, and feed that through a 1:10 transformer to get my 115 volts ac. In the US, we use 120 vac, so if I find a non rectified 12 volt wall wart, that's a 1:10 ratio right there. I can probably find them surplus. If I find something close enough, I can always adjust my rails to meet the needed ratio. Does that seem like a reasonable method of getting my 115 volt, 400 Hz reverence/power sine wave?Yeah, I have my work cut out for me!

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 20, 2015, 08:14:19 pm
content: I believe that Arduino is capable of the fundamental task of generating the three axis-phase signals. It is not fundamentally different than a phase-angle dimmer circuit which is quite common.I would start with a 115VDC signal, and use one output from the Arduino to generate the "reference phase" 400Hz signal. I would use a simple power FET to chop up the 115VDC into 115 V, 400 Hz square-wave. I would not think that your FDAI gadget will really care whether the signal is a nice sine-wave or simple chopped-DC. If it really doesn't like the sharp square-wave edges, you can always smooth them out with a big torroid inductor (exactly the same technology as used in larger lamp dimmers to reduce RFI and "fliament buzz".)The three axis inputs to your FDAI gadget are just phase-variations of the reference 115V, 400Hz signal, so it would be just a matter of using three additional Arduino output pins to send out three more copies of the reference signal, but phase-delayed to cause the display to show the desired information. This is also a relatively common methodology for vehicle dashboard needle indicators like speedometer and tachometer.

author: richfiles
author_rank: Regular Contributor
timestamp: July 20, 2015, 08:55:01 pm
content: It should be noted, that these 400 Hz synchro devices can, and sometimes do hum to the harmonics... I'd like to keep a clean sine wave to reduce all the lovely harmonics found in a square wave. As for generating the sine, that's the easy part. A MAX038 can do it with a trimpot to fine tune it. While the part is discontinued, it's easy to find online.Also to be considered... I have never done C in my life. I'm learning it fresh. If I can get the arduino to do a little math and then just send data packets to some digital pots, that works fine with me. I still need some room to program the output for the analog deflection gauge flight director crosshairs, and I need it to read an incoming data stream over serial from another arduino.The difference between software emulation is needing to software generate a sine wave, then calculate the attenuation of 9 sine outputs, at the resolution of the sine wave, 400 times a second... That's 10 sine waves being calculated, x 400 x the resolution... Per second. Double if I wanna beat the Nyquist value. It has to then output that... Your method has it chopping DC... But remember,I have to go both above AND below 0 volts, so it'd be more like plus and minus 162 volts DC... Gotta remember RMS.(irrelevant due to coupling)By going with the hardware sine generator, and digital pots, I only have to update it at the rate of change of the balls rotation... If the game is running 30 FPS, which seems a fair update rate, I only have to calculate the attenuation levels on the 9 outputs 30 times a second, or 270 trig functions per second, plus the assembly of the data packet, which involves some bit shifting and stuff, I think, to merge the commands, address, and data packets. I think it's 24 bits of data for a MAX5494 10 bit d-pot. That's 6480 bits of data... sent per second, to update all 9 pots at 30 updates per second... I think???

author: richfiles
author_rank: Regular Contributor
timestamp: July 20, 2015, 09:18:31 pm
content: Also... There is no phase delay involved in synchros. You'd be correct about phase shifting if we were talking resolvers.It's kinda... not obvious till you get it on an oscilloscope, and I had it wrong for years, myself. I did the same, and confused it for resolvers. Of course, it HAS been a decade since I built my last synchro at my old job. It;s only been a couple years since I last worked with resolvers.The input reference, and all three windings output sine waves that are in phase, either flipped or unflipped (positive/negative flipped around) in relation to the reference, but they are attenuated based on the phase angle of the winding to the rotor.Mike's Electric Stuff covers this quite well. Only polarity and amplitude shift, not the phase.https://youtu.be/fcoR8plMMK8?t=15m18sthere are three signals, per synchro, and a synchro per axis, so with 3 axes, there are 9 signals to the FDAI, plus the reference.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 20, 2015, 09:48:34 pm
content: You would be perhaps better off using AD633 as the modulation means, driven by a multiple DAC chip controlled by the Arduino. You'll need a few trim pots for the unused multiplier inputs. This eliminates much processing in the Arduino.Or find a 12Bit Multiplying DAC that is capable of AC reference inputs.Steve

author: Skimask
author_rank: Super Contributor
timestamp: July 20, 2015, 10:02:14 pm
content: I've worked on and recognize that ADI, but I can't place what aircraft it's out of...If I can throw a second idea out there that adds a 1/2 load of complexity...Get your hands on 3 more synchro transmitters and drive those with stepper motors...maybe???possibly???And you obviously won't need the full 120VAC to drive the synchros themselves. Worked in a flightline backshop for a bit. One of the checks was to run the AC voltage down to X volts and see if the ball still indicated correctly. If I remember right, 30-40VAC was good enough as long as the bearings were halfway good. Get one with really nice bearings in it and they would indicate fairly well down to 20VAC but stick once in awhile.

author: BennVenn
author_rank: Regular Contributor
timestamp: July 20, 2015, 10:05:07 pm
content: Or.... Find some smaler synchro's and tie them directly to your sychro's. All you'll need is the 400hz ref and a way to manipulate your master synchro's. Stepper motors?We have sychro testers at work which are just sychro's with alligator leads.We also have synchro to resolver converers which are just 3 phase transformers.Another idea could be use 3 ferrite transformers with 400hz AC input and the output going to your sychro's. Use a DC bias to control the output voltage of the transformer. Some of the older gear at work uses variable differential transformers so that is another method.Easiest would be the MAX038

author: richfiles
author_rank: Regular Contributor
timestamp: July 21, 2015, 12:51:59 am
content: Quote from: Skimask on July 20, 2015, 10:02:14 pmThis one, I'm told, came from an F-4 Phantom simulator. I've heard ADI many times before, but I'm so used to FDAI, due to references to Apollo that I come across, thanks to my being a Kerbal Space Program nerd!That's interesting to hear, regarding the lower voltages... I might have to try that.The ball sometimes spins a little just from inertia when I'm moving it around. Smooth as a baby's butt!I had considered driving it with steppers linked to synchros... If I could get three Tachtronic Instruments synchros that'd work with it, i'd LOVE that... Cause they'd have been built by people I knew... and if they were from 2004-2005... possibly ME!Still, I somehow like the idea of doing a design that makes it all solid state... I dunno. I STILL have to come up with the 400 Hz inverter. Do you have any details you can share on these things. I have this, so far...QuoteThat chip can has a 1974 date code!!! She's half a decade older than I am! O0Can i ask, this "grease"... Is that from the gasket breaking down, or is this something i should be concerned about... The thing was just sticky around the seam.Fortunately, The Kerbals GOT another gimbal for Kristmas... So they don't have to worry about gimbal lock!

author: daveatol
author_rank: Regular Contributor
timestamp: July 21, 2015, 01:00:40 am
content: The arduino shouldn't have an problems generating the required signals; there's only a a single sinewave to generate, and all signals are just a scaled version of that. Integer multiplication is fast on the arduino, so there shouldn't be any performance issues there.You can get the nine analogue voltages using a single DAC, a MUX, and nine capacitors (see attached circuit - sorry I drew it thinking there were only 7 channels; add another MUX to get the additional channels). The DAC generates the voltage for all channels in sequence, while the MUX is used to direct the voltage to each of the caps. The MUX should be directed to an unused output between changing DAC samples to stop glitches occurring at the used outputs. The voltage on the caps is then buffered and fed to the AC-coupled transformers (or AC-coupled transformer drivers).

author: Yansi
author_rank: Super Contributor
timestamp: July 21, 2015, 01:16:10 am
content: Arduino is maybe bendable to do something here, but in my opinion useless. I'd rather use some more sofisticated chip, at least with threephase complementary PWM peripheral (like tiny261 or AT90PWM3 if you like the AVRs so much - I don't) with brake input (OC protection) to generate the threephase power signal using a threephase bridge and LC reconstruction filters (if needed, I don't know the exact construction inside the device) with a dc bus link voltage of 163V (using third harmonic injection modulation type).I am quite not sure about the other part, because I haven't understood clearly what the unit outputs and what should be processed. Is it some kind of a threephase resolver thingy? But it is indeed interesting one. Never seen anything like that. Only yrs ago, I have built a few 3ph supplies of 28V~ and 400Hz for gyroscpoes.

author: richfiles
author_rank: Regular Contributor
timestamp: July 21, 2015, 01:18:07 am
content: Quote from: LaserSteve on July 20, 2015, 09:48:34 pmCertainly an interesting chip, but I'm not sure it gives me much in gains for processing. I'd still need to update a DAC at the same rate as the d-pots (30-ish updates per second, x 9 DAC channels, still needing to calculate the attenuation using trig functions). Therealdifference is I get to use a higher resolution DAC to feed this thing it's analog multiplier (in this case, attenuator) value. Trying to just do it all in software though.. I have utterly no idea what a little 16 MHz chip is or is not capable of, nor do I know what the limits of the Arduini C language are, but I still have no ideas if it's really genuinely possible on an arduino to calculate and render 10 sine waves, all at different amplitudes... Maybe it is. Probably possible if you know what you're doing, but I don't. Still just learning.What I do tend to feel more comfortable with though, is hardware. I guess that's why this seems like a reasonable option to me.One thing to consider is price. I'll need 9 attenuation channels, and these are easily 3-4x the price of the digital pots, even the 1024 step ones.Hmm... If you have a linear pot... Is there any type of circuit that would attenuate an AC signal by the RMS value? I hope that makes sense... If I had a circuit that could do that, then I could spread out my resolution more uniformly along the sine wave, focusing more of the resolution where it shallows out at the peaks, and dropping resolution at the zero crossing.Is that even a thing? Can it be made to work off a linear pot?

author: richfiles
author_rank: Regular Contributor
timestamp: July 21, 2015, 01:35:19 am
content: Quote from: Yansi on July 21, 2015, 01:16:10 amThe biggest difference between a synchro and a resolver, is that resolvers use phase shift to read angle of the input shaft. Synchros use amplitude modulation of three IN phase signals (though they can flip over the zero crossing, so they appear 180° out of phase... It's a literal polarity flip, as opposed to phase shifting, in that case)Quote from: daveatol on July 21, 2015, 01:00:40 amTrue there is a single sine wave, but the attenuation factor is not going to be an integer. It'll be a floating point (I assume floating point) trig function... Either the sine or cosine of the rotor angle or something like that. Not really so sure it'd be zipping by on integers. I have a 240p grainy video that explains the maths... but it's... It's also a real SLOG...Quote from: daveatol on July 21, 2015, 01:00:40 amWell this is certainly interesting!

author: daveatol
author_rank: Regular Contributor
timestamp: July 21, 2015, 01:55:28 am
content: Quote from: richfiles on July 21, 2015, 01:35:19 amYou will already have a lookup table being used for the sinewave that you're driving the DAC with. Therefore it takes a single lookup to calculate the sin or cos of an angle.You said that a 12-bit DAC would be ideal; with such a small dynamic range, floating point is not even attractive. FYI fractional multiplications can be done efficiently using integer multiplications. e.g. if I want to multiply my 16-bit value by sin(25°) = 0.4226..., I can multiply by 27697 (which is 0.4226.. * 65536) and then divide by 65536. The division is done by ignoring the lower 16 bits of the multiplication result (because 65536 is 2^16), and consequently doesn't use any processing time whatsoever.I didn't watch the linked hour-long video. Perhaps you could summarise/transcribe the pertinent formulae.

author: richfiles
author_rank: Regular Contributor
timestamp: July 21, 2015, 02:13:37 am
content: https://www.desmos.com/calculator/kt7yt0gz5mThis is a link to a graph. The table indicates the limitation in using a 10 bit digital Potentiometer. Put simply, the resolution is extremely compressed near the zero crossing, and extremely sparse at the peaks. at the peaks, I get over a degree of change with a single step. At the zero crossing, I only reach half a degree in 5 steps! Fortunately, the resolution quickly jumps to a degree per step by the thirds step from peak, and then by the 6th or 7th step, it's getting near to half a degree per d-pot step. The other two outputs will never be near peak when one output is there. They will be in a more median range. Will their finer resolution compensate then, for the lack of resolution at peak? I imagine even in the analog domain, this has to be a weak spot too.maybe It'll be fine, and I'm just over thinking things.I'll have to perform the trig function off the winding's angle in relation to the others (output x, y, and z is 0, 120°, and 240° respectively, from the null angle). Then I'll have to scale that to 0-1023 and round it to an integer of that, to derive my step position.

author: richfiles
author_rank: Regular Contributor
timestamp: July 21, 2015, 02:35:14 am
content: Quote from: daveatol on July 21, 2015, 01:55:28 amActually, if using D-pots, or using a DAC with those multiplier chips... My 400 Hz sine wave never enters the arduino. It'll come from a MAX038. The D-Pot or the multipliers (used as attenuators) simply get set to a level that then attenuates the sine wave that is sent into the device. If the navball is static, then I'd be driving DC from the DAC, or keeping the D-pots fixed at a particular set of steps. I'd still need the trig library (assuming this installs the lookup table as well)I DID consider another option that would double my D-pot resolution... If I reference one side of the D-pot to ground, and then have 9 digital outputs from the arduino attached to a half H-bridge type circuit, I can reference either the positive or the negative supply rail, and it will only ever switch when the d-pot wiper is stepped to ground... aka, at the zero crossing.Using 9 digital lines from the arduino and a 1024 step pot would net me a 2048 step pot (with minor support hardware). That reduces my dead zone to 90° - 87.46765° = 2.53235°, and the second step is already 1.04922°, and the third step is already sub 1° at 0.8053°! Combined with the fact that even with the low resolution at peak, the other two outputs will have nominal sub degree values... I think it might work!not to mention, basic op amps and the d-pots are dirt cheap too. Going with surplus wall wart transformers ought to get me a good, low cost transformer to step up, and going on Skimask's suggestions, i likely don't even need to drive this all the way to 115 volts.***EDIT***Maybe... I was originally going to pass the sine wave through the pot, with one side if the pot tied to ground, and the other tied to the reference. The wiper would be the output. It's 10 PM here, and I can't think... I'm mixing DAC generated sine with d-pot passthrough... ugh!I suppose, I could try something else... If I created a voltage divider between the actual sine wave and ground, and tied the "ground" side of the digital pot to this point, it ought to give a range between 0 attenuation, and I'm not really sure... This is... I think it would alter the range, for sure... Plugged it into a sim.. It's weird... I imagine it would take some crazy tricks to make work... It does give me two ranges, but not like the other idea... The other idea toggled my supply rails at the zero crossing. This gives you a 0-full range and a half to full range, but does not switch at zero... I don't like that at all. It won't be simple to implement, and the rise times of the sine waves will be off due to the different ranges. DEFINITELY a NO GO. I'll leave the pic for LOLs.A BETTER idea, might be to rectify the sine wave, and then have a digital I/O tied to the amplifier to amplify it either positive or negative. That gets the zero crossings back, and solves something I TOTALLY missed... The pots can attenuate, but not flip the polarity. I need to be able to flip the polarity.Fortunately, relying on the arduino to select whether to amplify each signal positive or negative both solves this, and provides 1024 steps for a 0 to 90° zero to peak range, rather than splitting 1024 steps between -90 to 90°. I need to have an input that detects zero crossing if I do this though... Dang it.. the pots were so cheap too!If I use DACs and tie that to an op-amp... I could have a better range (since 12 bit DACs are common enough, I believe) and I get my polarity reversals by inverting the op amp with the bias signal. I'd get the attenuation AND the polarity flip when the DAC flips... Right?Okay...I think what I need is a DAC to output the attenuation level/polarity, and that needs to feed into an op amp circuit that actually performs the attenuation (and can invert the input when the bias inverts). If I do a 12 bit DAC, I get reasonably good resolution, in both the positive and negative (quadruple the number of steps as the d-pot).Since I need to pass the output through an amp anyway, this also saves me the effort and lets the attenuation happen right in the amp.Okay... Now I need a good amp circuit that will attenuate a signal with a DC bias input, and invert it when that bias goes negative.I need to go to bed though...

author: zapta
author_rank: Super Contributor
timestamp: July 21, 2015, 02:52:25 am
content: You can buy off the shelf digital to synchro converters. For examplehttp://www.ddc-web.com/Products/83/Default.aspxThere are others.Also, a synchro resolver can also be used as a transmitter so if you connect a step motor to a synchro it can act as a D/R.

author: daveatol
author_rank: Regular Contributor
timestamp: July 21, 2015, 03:24:18 am
content: The MUXes aren't usable for attenuating the signal. If you use the circuit I showed with a 14-bit DAC (e.g. AD5641 is 14-bit >100kSps for $1.72), surely you can get the resolution you're after. The arduino just has to feed a constant stream of values to the DAC, and update the MUX. Assuming an DAC update rate of 50kSps, that's 13.9 samples per cycle of the 400Hz waveform.I like your idea about inverting the signal as a way to get an extra bit.Of course you can use the digital pot approach, I just have the feeling that readily available DACs generally have higher resolution (I haven't looked in a while though, please correct me if this has changed).

author: daveatol
author_rank: Regular Contributor
timestamp: July 21, 2015, 03:30:18 am
content: Also, what happens if you try to drive a synchro with DC current? Does it become magnetised or something? If there's no magnetisable material in the synchro, then I'd expect that DC could work fine.

author: Skimask
author_rank: Super Contributor
timestamp: July 21, 2015, 03:34:03 am
content: Quote from: richfiles on July 21, 2015, 12:51:59 amThat's it...the F4G. Didn't really work them so much as got a bunch of training on them. FADI, ADI, same, same overall. I think about the only difference, in my view, is the FADI has azimuth markings on the ball. ADI, no azimuth.QuoteThat'll be misleading at best if I remember right. Bearings good, windings/contacts old, needs more vitamin VAC. Windings/contacts good, bearings old, still needs more vitamin VAC. Like anything else, try it until it fails and back up one step.QuoteGot a 3-D printer? Build your own synchro TX.I know..I know..sounds easy in theory. Getting it to work right, another story entirely...QuoteNot only that, but you have to come up with a 3 phase 400Hz inverter, at a reasonable cost.QuoteNothing more than you have already. Synchro signals 120VAC, 3ph, 400HZ. All of the flags, pointers, etc. should be <1V DC to pull them in or out as needed. Like anything else, throw a volt at it thru a current limit resistor, see what the flag does. Increase or decrease as necessary.I just had another look at the pictures. That recessed cannon plug placement is just like the old ones they used to use on the ADI's on the tankers (C-135's) and B-52 bombers (and probably a hundred other aircraft types). Even with a cannon plug pliers, made it a bitch to get the thing on or off. Half the time, I ended up using a straight edge screwdriver and making gouges in the cannon plug outer shell to get it to lock or unlock.

author: Someone
author_rank: Super Contributor
timestamp: July 21, 2015, 03:37:05 am
content: AVRs at 16MHz will have no problem generating the signals you need, even software PWM of the output ports will suffice when the final result is a set of synchronous 400Hz sine waves. The trick will be narrow bandpass filters that will have the desired settling time, then you can dither the PWM to get enough resolution in the final waveforms.

author: richfiles
author_rank: Regular Contributor
timestamp: July 21, 2015, 04:21:55 am
content: So digital pots are pretty much out... cause I had a case of the dumb and forgot I needed the ability to INVERT the signals.I GUESS if I used an Arduino(s) with at least 10 total PWM outputs,I suppose it might me possible to render the sine waves via software... People seem to be saying it's possible.**NO! Just, no!**I've considered splitting each of the three axes across three Pro Minis (they only have 6 PWM pins). One of them would need to generate the reference, AND they'd have to all stay synchronized... Maybe one could do two axes, and the other could do 1 axis, and the reference, plus the two remaining PWMs could operate the horizontal and the vertical parts of the crosshairs.Or I could use a Mega... I currently have a pair of Mega 2560s and 4 of the Pro Minis.I have ZERO C experience... So the idea of doing this all in software is... a pretty big jump for me.Would a pile of small DACs be best, or a pile of code???

author: richfiles
author_rank: Regular Contributor
timestamp: July 21, 2015, 05:09:04 am
content: Quote from: zapta on July 21, 2015, 02:52:25 amWhat's the old saying... If you have to ask how much... You can't afford it...Darn "Request a quote" buttons... That's exactly what those mean!Sadly, I'm on a tight budget. I've spread the collecting of these parts out over about half a year (the FDAI and Arduinos were just my latest purchases). My job sucks... but it's incredibly stable, and may have LONGterm options to move up... As in it may take a long time to move up... But it may happen in time.At least I got a good raise last week!Part of why I want to do this, is not just for myself, but for the small circle of people who want to give this a try, but generally would get wiped out just buying the FDAI itself. In that sense... It DOES make sense to try to do as much in software as possible. It's just REALLY intimidating to go into learning a programing language ENTIRELY from scratch, haver having not touched programming since Commodore 64 BASIC, and TI-89's TI-BASIC. Not to mention the fact that the task I'm wanting to do isverycomputationally intensive, considering the tiny devices that are meant to run it. Part of me doesn't know what the capabilities of these microcontrollers really are, and for me to be learning a programing language I've never used before, AND have such a big project... I guess my natural instinct is toadd moar chips! I'm used to watching sine waves plot in real time on those old graphing calculators, and then expect to do that 400 times a second, times 10!I have zero experience with microcontrollers, and as a result, I've not built up confidence in knowing what I can and can't do with them.I've spent more time thinking about how I might do it, and haven't tried a thing.So, both the Pro Mini and the Mega 2560 have a 16 MHz chip. The big difference is in the I/O and memory. The mega has 8K of SRAM, vs the Mini having only 1K. Should I just start on the Mega? Is there even a possibility of fitting lookup tables and all the needed code to do this on the Pro Mini? Does a trig lookup table get stored in the flash or eeprom, or does it load into SRAM for use?Lots of noob questions and noob thoughts here!

author: daveatol
author_rank: Regular Contributor
timestamp: July 21, 2015, 08:28:05 am
content: Quote from: richfiles on July 21, 2015, 04:21:55 amThey're not out; you just have to shift the signal (using AC-coupling) to the appropriate level. So, if you sinewave is ±2.5V, you reference it to 2.5V for a 0-5V range. After the pot, you can couple it to 0V for a 0V-centred signal, or leave t as is if you're using some inverter... but if you're using an external sinewave source you wouldn't be using an inverter for the extra bit of resolution.Quote from: richfiles on July 21, 2015, 04:21:55 amThe lookup table would take up 180 bytes for 16-bit samples or 90 bytes for 8-bit samples, assuming degree resolution (only 0-pi/2 is required due to symmetry). This project doesn't sound computationally intensive at all; the microcontroller shouldn't break a sweat.I'm not so confident about using PWM; you'd need heavy filtering to get a sinewave. It may or may not be a good option.

author: richfiles
author_rank: Regular Contributor
timestamp: July 21, 2015, 01:30:44 pm
content: Quote from: daveatol on July 21, 2015, 08:28:05 amLevel shifting is no problem. I was going to be using dual supplies initially. The issue is actually flipping the polarity... Sine wave peaks become troughs, and vice versa.Quote from: daveatol on July 21, 2015, 08:28:05 amSo... If I can make all 10 sine waves inside... How do I get them out? I've read about filtered PWM, and it seems... not perfect. Other than that...I read about ports. Being able to lay several bits down at a time to update all the pins of a port at once, but it seems like there are risks if you screw up stuff. DigitalWrite seems to be to slow to be of much use with regular pins.So basically, it's not "but we couldn't fit it all in", but is instead "how do we get this through the door"? I think that was my initial reasons to consider hardware. I can easy output serial commands.Still... Is there a way to do this...regarding PWM, one o my concerns is that it seems the PWM frequency is already quite low, according to some sources I've read. Is this adjustable. Likewise... Since this circuit will ALWAYS be dealing with 400 Hz, and never any frequency faster or slower... How tightly can we tune a filter for the output?

author: BennVenn
author_rank: Regular Contributor
timestamp: July 21, 2015, 09:57:41 pm
content: Wow this is getting complicated! It doesn't need to be!Offload as much as possible to analog circuits. 400hz sine generator? Couple of op-amps. Easy. SPI digital pots? Cheap and simple to drive. Small look up table in the AVR. You wont need much current to drive the synchro, a nice low impedance driver coupled to an off the shelf mains transformer will do.If you are using an Arduino, it becomes even easier as there are Sine/Co-sine math libraries available.No need to generate multiple 400hz signals (in phase) from the AVR.

author: richfiles
author_rank: Regular Contributor
timestamp: July 22, 2015, 09:04:31 am
content: Quote from: BennVenn on July 21, 2015, 09:57:41 pmThe issue with the digital pots though, is they attenuate just fine, but I need to be able to actually reverse the polarity of the sine waves as well, without losing resolution. Even if I do that, I'm looking at ganging a minimum of two d-pots together, and selecting them with a mux. I'd have to generate an inverse of the reference, and select (with the mux) the wiper attached to the inverse sine wave. The middle of the two d-pots would be grounded.[uninverted sine]-vvvv--vvvv-[inverted sine] A mux selects which wiper to read, to output the inverted or uninvited sine.The reason that [uninverted sine]-vvvv-[inverted sine] isn't viable, is that even though the two waves ought to cancel each other out at the center wiper position (I think), it's be such a significant drop in resolution, that the peaks would see a few degrees between d-pot steps. And that could mean the navball would jitter and/or jump around at those peaks. 10 bits of resolution is already barely tolerable, and still leaves poor resolution at the peaks. I can't even find d-pots better than 10 bits yet. a DAC isn't bad, as you can easily find 12, 14 and even 16 bits of resolution.Relying on d-pots puts me at requiring a minimum of 18 d-pots, 9 channels worth of mux (probably 2-3 chips worth, cause OF COURSE I'm using more than 8 channels), a sine generator that can create synchronized inverted outputs (a pair of op-amps in opposing polarity from the sine source), and my output amplifiers that lead to the output transformers......Versus figuring it out in software... the software being the more complicated option...With software, all I think I'd need is a tuned LCR type filter at each of the PWM outputs, fed into my output amplifiers that lead to the output transformers... It'd skip all the d-pots, muxs, and the hardware sine source altogether.I AM a hardware guy... My first instinct was to rely on support hardware,but even I am seeing that the support hardware is gong to add up very fast, in terms of complexity.As I stated earlier in this thread, I'm trying to do this as a low cost alternative to spendy commercial units that are sold by companies that won't even publish the unit's price without a quote request... This project is intended for people like me who manage to snag the un-likely FDAI/ADI unit on ebay, but have no means of controlling it.Now... if you want a SIMPLE hardware solution, the easy method is to just buy three synchros, three motors (stepper or DC, with encoder), and just run them together with a simple mechanical linkage. Position motor, navball moves. That's simple hardware. The reason I haven't done that already, is that most of the cheap synchros are in the 11-28 volt range.I'd still need to run those signals through 9 transformers to bump up the voltage for the FDAI I have. I only need one reference sine source and one step up transformer if I snag 115 volt synchros. Most of the 115 volt synchros are spendier,and I haven't received my next paycheck yet. The FDAI wiped outallthe spare change from my last paycheck... and the one before that...**Edit**Later on, I come to find info that suggests only the Reference/Power is 115VAC @ 400Hz. I belive the rest of the inputs are lower voltage, probably 28 volts or less.

author: richfiles
author_rank: Regular Contributor
timestamp: July 22, 2015, 09:47:31 am
content: From what i'm getting... My structure would need to be something like this:1: Initially set my variables and what not up, preferably setting them to a default zeroed state, since the game won't necessarily be sending ANY data until I am in a vessel. This would set my yaw, pitch, roll, and any other statuses that I have the arduino handle to default values... North facing yaw, level pitch and roll. I'd initially calculate the multipliers for the nine synchro outputs based on these three initial values (I can actually do this the easy way and PRE calculate them... I'd just preload 9 constants, and some of them might actually all be the same, since the ball is effectively set to "home"). This would also set the sine wave timebase to a starting value of zero.2: I'd have a process that creates the reference sine wave, point by point, based on either a lookup table or the library that adds sine functions. this function would look at the time between the last time the timebase was set and the current moment, to determine the change of angle of the sine wave. the timebase is reset as well.3: I'd take the existing calculated value of the sine wave and multiply it by the 9 multipliers to get the 9 synchro outputs. negative multipliers would flip the waves for those outputs that need to be flipped.4: I would scale and round the 10 waves to values to be sent out to the PWM channels. The outputs would be updated with the new values.5: the process is repeated from the step 2. The time base has been counting all the while from the completion of step 2. This provides step 2 the means to calculate the change in the sine wave's amplitude over time based on the exact angle of the sine wave at the moment of it's calculation. It also accommodates any delays that might occur in regular processing, due to, say, interrupts...6: such as receiving serial data and updating the multipliers. I'm guessing, from my limited knowledge on modern programming, that one could use interrupts to redirect focus on the serial port if an incoming data steam is detected. Upon receiving updated values for the angle of yaw, pitch and roll, it would perform the 9 trig calculations to calculate the multipliers for the 9 outputs based on those 3 values, and then store those values, returning to step 2.In this structure, you could have the program take extra cycles to receive data over serial, and update the multipliers. The next sine calculation might have a hiccup in the resolution, but would not screw up the timebase, and the external passive filters should smooth it all out.I think?!*NotObviously, this is a FAR way away from code, but does the structure seem reasonably valid?

author: BennVenn
author_rank: Regular Contributor
timestamp: July 22, 2015, 10:02:45 am
content: In regards to inverting the sine wave, use the inverting input of an op-amp? I'm sure you could rig up a differential op-amp with say... 1/2 original sine wave then depending on the amplitude of the reference sine (sine passed through digital pot) it would output anywhere from in phase at full amplitude to 180deg out of phase at full amplitude varying as much as your digital pot has resolution.Op-amps are cheap, PCB transformers can be had in a fairly small form factor.Also available are SPI driven 6 channel audio DAC's used in CD/DVD players. These are only a dollar each on aliexpress and have something like 14bit resolution and can all by sync'd to a master clock so they remain in phase. That is if you are set on using an arduino to generate waveforms.

author: richfiles
author_rank: Regular Contributor
timestamp: July 24, 2015, 05:32:31 am
content: Quote from: bench_knob on July 22, 2015, 11:18:33 amThe servos are still pretty unique. They are a 2 phase motor, with a synchro mechanically linked into the gearing. The amplifier on the rear of the unit already is designed to drive the servos based on the synchro error. As for RC servos... They willneverbe as durable, or as quiet as the existing precision gear train. Furthermore, there are plenty of misconceptions about RC servos. Put simply... RC servos and servos are not the same thing. They have no absolute position feedback. That is necessary for accurate ball positioning.Besides... Two of the motors and two of the synchros are actually inside the ball! That's precision engineering youdon'twant to screw up by taking it apart.Since this is a hobby project, my aim is very simply to see how low I can keep the costs. Worst case scenario, All I really need is three synchros, a function gen made into an inverter with an amplifier and a transformer, and mechanical linkages to three stepper or DC motors with encoder wheels. Then I could use the standard motor libraries to position the ball.That's relatively simple, but it still requires getting synchros and putting together mechanical linkages and stuff. I'd still need to do the inverter for the reference sine source. I want to try to do this all solid state, and all on the cheap. Quite frankly, I want to build something CHEAP forhobbyistsBECAUSE of how freakin' expensive a lot of this "premium" aviation equipment is. I get it, planes are expensive... Doesn't mean a hobby grade sim should be too. The way I figure, the FDAI is expensive enough to get, all on it's own... If I can do this with an arduino, a handful of cheap op amps, optional DACS, preferably some passives, and some $1 surplus transformers (I found some that I think will work... They have the right ratio to bump arduino level voltages up to 115 volts)... Well... That's my goal. I want to do this cheaply, and share how I did it, so if anyone else decides they want to do this, they can.That's my goal anyway.Also, it's alearning experience. Can't argue with that!I think I might give a homemade navball a shot someday. I want to get/make a 3d printer, or to fix the Z axis on my mill, and actually get my current project done before I even remotely begin to consider that.

author: Wolfram
author_rank: Frequent Contributor
timestamp: July 27, 2015, 11:32:38 pm
content: As suggested earlier, a pair of regular op-amps would make a more than adequate 400 Hz sine wave oscillator, no need to use anything as fancy as the MAX038.The inversion of the waveforms could be done by making an inverted version of the 400 Hz reference, then selecting between the non-inverted and the inverted version before each pot. This way you wouldn't need any extra digital pots. Something like a 4053 multiplexer could be used here.To spread the resolution out over the entire range of the synchro, you could modify the "law" of the digital pots using a resistor like shown here:http://www.geofex.com/article_folders/potsecrets/potscret.htm

author: richfiles
author_rank: Regular Contributor
timestamp: July 28, 2015, 02:53:14 am
content: I found the MCP4725 12 bit I2C DAC is more than sufficient for the resolution I need, and it's relatively cheap.I have an offer submitted (via ebay) to get 10 for $30 USD. I'll have to manually address them with the external address set pin, since the chips only support 8 addresses, AND two of the bits are factory set.I have plenty of I/O for that though.I'll feed the output of each DAC to an amplifier that can drive the 10 small transformers, and that'll be it for hardware! DAC, amp, transformer, FDAI.Software wise, I will have all the precalculated sine values in a table stored in flash. I will then multiply the current value of sine with the 9 calculated multipliers and then update the DAC value for each of the 10 DACs. Every time I receive updated yaw, pitch, and roll angles from the serial port, it'll calculate the three new multipliers for each of the three axes, and then each step of the sine wave will then use the new multipliers, till the attitude data is sent again and received over serial.The hard part, for me, is simply that I have so far to go in terms of learning C. I get the gist of some parts of existing code, much of the time, but I simply don't have the skills to understand it all, much less create original code, yet.On a completely unrelated note, I ordered a bunch of other stuff too. Chips for driving my 4-20 mA GE 180 series edgewise meters, a dozen 8 digit green LED display modules, some really dirt cheap amplifier boards that I'll give a shot at driving the DAC output (so cheap, it's worth the gamble if it works, and no loss if it doesn't), a pair of proto shields, and one of those vacuum part picker-uppers. I hear they rock for SMD components. I also found a similar series of military spec sealed switches practically identical in style to the ones that they used on Apollo. Honeywell makes them, and OH MY... Some of those switches were $60-130 USD!!!Fortunately I found some Chinese switches at 10 for $7 USD, that while not identical... ARE PERFECTLY GOOD ENOUGH to satisfy my wallet!

author: daveatol
author_rank: Regular Contributor
timestamp: July 28, 2015, 03:39:49 am
content: So you're going for separate DACs for each channel? I kinda liked the multiplexed version.I have one thing to add which may make things simpler. With three phases, you can get away with only two transformers. You only require two DACs per three-phase motor, for a total of seven DACs and transformers for three motors and a reference. The third phase is simply held at a reference voltage (which can just be 0 volts, or floating), and the other two phase voltages are referenced to that point.

author: richfiles
author_rank: Regular Contributor
timestamp: July 28, 2015, 04:23:19 am
content: Quote from: daveatol on July 28, 2015, 03:39:49 amSorry, synchros are not motors, and there is no phase difference. It's the amplitude and polarity relation between the three windings that creates a current in the rotor of the sensing synchros that is non zero, and polarized to the direction of the error of offset. That feeds into an op-amp circuit that drives a 2 phase servo motor to adjust out the error till it nulls out to zero.Synchros are used in pairs. A synchro transmitter, and a synchro receiver. They connect over the three windings, with the reference fed into the transmitter, and the rotor of the receiver compared to the reference to find the error of the rotor angle between the two.All three windings are required to represent the rotor angle. You might be able to cheat a little on motors, but not on synchros. Remember... All nine output sine waves are at matching phase relation with the reference. Those angles do not deviate. Even saying 180° for the reverse polarized waves is misleading... It's an actual polarity flip, and not a shift in phase. If you had a glitch in the reference, it would still happen in phase with the reference... just polarity flipped, and not 180° out. There is a three way differential effect that directs current in and out of the three windings that represents the angle of the rotor, withnophase shift in the signal.Synchro sensing also has a poor "resolution" at the sine peaks. It relies on the other two windings to fill int he detail during these peak reversals, where there is low change of the signal. having a winding sit at reference actually carries angular information, in relation to the other two windings.

author: daveatol
author_rank: Regular Contributor
timestamp: July 28, 2015, 06:12:37 am
content: Quote from: richfiles on July 28, 2015, 04:23:19 amSorry, I miswrote (and I'd switched back to thinking of three-phase motors). I believe what I stated still applies (if you substitute "three-phase motor" with "synchro").If you have a set of windings set up in star configuration, as you would for a synchro, with the three connections named A, B and C, and the junction point named J, then I would say that the following equations hold true (if I understand what you said in post #13). I have tied point C to ground (0V) to simplify the equations to only two variable amplitudes. Phi is the "null" angle, x(t) is the 400Hz sinusoid.

author: richfiles
author_rank: Regular Contributor
timestamp: July 28, 2015, 07:32:54 am
content: Okay, so what you're saying, seeing as how the 3 windings are floating independently from the reference going into the rotor and the sampled rotor winding from the receiver synchro... You're basically just saying you are "un-floating" it, buy binding one winding to ground, and letting the other two windings effectively compensate by integrating the difference that would normally be carried by the now fixed winding. The Y ends up carrying the amplitude value against the now fixed winding, putting an offset on both other windings.I think I get that.How does that effect my resolution though, particularly when one winding goes to a peak? Yes, reducing the count of windings cuts costs of extra hardware by almost a third, but I don't know how that will effect my signal at those peaks. It does reduce the data transmitted by 1/3 as well. The two retained phases don't gain additional data density. Of course, 12 bits is NOT a bad resolution at all. It's a far cry from the measly 8 bits the Arduino can generate by PWM, that's for sure. Even 10 bits was still not sufficient for even a degree per unit of resolution at the sine peaks. 12 will cover that. I have not calculated for 11. My goal was a minimum of 1/3 degree per unit of resolution, but despite the poor peaks, the other two outputs sit at areas of finer degrees per resolution, I think making up for that. Cutting down to one other winding to make up for the resolution isn't ideal. Parts are ordered anyway.Maybe it's something I can experiment with. See if the two phases can maintain smooth rotation of the ball.*Naw, I'd rather just build the best option up front and just get it workingOne of my concerns, and a reason for going with a higher resolution hardware option is that these FDAI devices can hum. It is a mechanical device with a 400 Hz signal being pumped in. Ideally, it's not prominent, but itcanbe, particularly if it is oscillating between coarse degree divisions, that hum could become louder. I'd like to avoid that.

author: daveatol
author_rank: Regular Contributor
timestamp: July 28, 2015, 08:00:12 am
content: Quote from: richfiles on July 28, 2015, 07:32:54 amMy quick calcs in a spreadsheet show that when the value of the phase A-C is changing slowest, the rate of change of the value of phase B-C is changing fastest. This may not be what I should have been calculating....You should work it out yourself to see if it's good enough for your application and not take my quick calcs into account though.

author: richfiles
author_rank: Regular Contributor
timestamp: August 27, 2015, 09:43:24 pm
content: Well,i have the DAC + Amp wired up.I think i actually will need more current for the Reference, as it also appears to power the FDAI, but I have some LM675 power op-amps in reserve that I can drive in a a unity gain configuration.I still need ten transformers to perform my step up. Anywhere between 70-115 volts is my aim.The blue boards are small LM386 audio amplifiers. The red boards are the 12 bit DACs. Yes, i went old school and wire wrapped the puppy up!Pics are ALMOST final... I took these before one last connection on all but one output. They are actually done now.

author: richfiles
author_rank: Regular Contributor
timestamp: October 21, 2015, 06:30:11 am
content: *Please Note: This is mostly copy paste, with some edits, from my post at the Kerbal Space Program forums... I occasionally over explain things that we ALL ought to know around here!*So, I was doing some math... and I believe I have a major issue... and itis major... I don't think my current DAC design has achanceof working.It puts 100% of the workload on the Arduino to generate all 10 of the sine waves required, all at 400 Hz, with realtime waveform generation. Some basic math tells me this is a gargantuan task. Besides monitoring a serial input for axis updates, I need 10 sine waves. I can do MOST of the work using lookup tables, but I still need to calculate the offsets of yaw, pitch, and roll (by adding 120° and 240° to each of the three values) and looking up the attenuation values for each of the 9 results from a lookup table, for each data frame sent by the game, assuming 20-60 frames/second. I need to then multiply the reference sine wave (which can also be generated by lookup table) with the attenuation values (9 multiplications), and send the reference and the 9 results of the multiplications to the DACs, which requires 10 I2C transmits, with a digital out changed between each transmit to function as a chip select. These multiplications happen at the sampling rate of the sine wave, not the frame updates. I only update the multiplicationvaluesonce (x9) on each frame update.If I need even 256 steps in my sine wave cycle (that's a low resolution, but It's my attenuation resolution that defines the angle of the navball, and temporal resolution would be somewhat smoothed out by filtering), then the math works out as follows:At 400 Hz, if I have only 256 "slices" of the sine wave over one cycle, and 10 sine waves to update, I have to write the I2C bus 1024000 times EVERY SECOND... I... Is that even possible? I am fairly certain this exceeds the maximum data rate for I2C. There appear to be 4 speed standards: 100 kbit/s, 400 kbit/s, 1 mbit/s, and 3.2 Mbit/s... Even the fastest speed wouldn't handle the bandwidth of just 8 bits sent at that rate, and these are 12 bit DACs! If I could get the resolution out of the PWM to do it, it might work, but the PWM resolution isn't even high enough for one whole degree of ball rotation per step! Ouch! That's one jittery navball there!I may reuse my DAC board for analog meter movement, if I can mod the amps to drive DC (they are audio amps, and can only drive AC, but I think that is only because they are AC coupled with a capacitor inline with the inputs and outputs). If I simply remove the amp boards and drive with a MOSFET or something, it will probably work fine. That could be a reasonable use for the I2C DACs. As it stands, the $40 or so dollars spent on my DAC board, and the time spent building it, are more or less wasted.So...The solution is VERY simple and elegant, and thanks to some part finding by someone on the Kerbal Space Program forums, far less expensive than I thought! It's still more expensive than my original plan, and more complex, hardware wise. It REALLY DOES solve my problems though. That part, is the 12-bit MCP4912/22 DAC.I need to use a totally different type of DAC. I need one with a proper adjustable voltage reference, and the MCP4922 has it. All I need to do is generate a single sine wave with a hardware sine wave generator (can be done with either an analog circuit, or the $7-12 MAX038 chip that swarms ebay). I just set it to produce a 400 Hz sine wave, and that's it. I need to feed that to a pair of op amps to create a differential pair (opposing cycle polarities), and use an analog switch to select either the un-inverted or the inverted sine wave to feed into the DAC's voltage reference.This is:1 hardware 400 Hz sine wave generator.2 op-amps to create inverted and non inverted outputs.20 analog switches (about 5 chips) to select whether to flip or not flip the reference sine wave.9 DACs with adjustable voltage references.10 power amplifiers driving transformers that drive the actual FDAI at the desired higher voltages.So, the adjustable voltage reference input is the real trick to making this work. It's been brought up in pervious messages, and it WAS the correct path. If you have 0 attenuation, then the DAC is at maximum output, but the output will scale to the voltage reference, so as the sine wave applied tot he voltage reference rises and falls, the output matches it. If the attenuation were at 100%, then the DAC output would be at it's minimum, meaning no matter how high the input sine wave rises and falls, it's scaled down to nothing. As the attenuation scales between 0-100%, it scales the actual sine wave that is being input on the voltage reference.The DAC basically just becomes a hardware attenuator. I MIGHT be able to reuse the amplifiers I installed on the DAC board by desoldering them. I may need to drive a power op amp though, to push enough current into the final transformer stage, in order to have enough power to actually drive the FDAI. I have around a dozen LM675 power op-amps that I hope can do the trick. Those were not cheap, but I already have them. I may end up needing to hand wind my own transformers, just to keep myself on budget. I have no idea what it'd cost me for 9 transformers to bump the voltages driven by the low voltage DAC circuit, to the 28 volts wanted by the FDAI.This is actually an area where I am actively seeking advice. I need to take what will likely be a 0-5 volt sine wave (zero crossing at 1/2 Vcc), and will need to convert that to 28 volts. I DO have the LM675 power Op-amps that I can use as output stages. The transformers will all have one side of the primary tied to the signal, and the other side tied to ground. The secondary will have the center of the "Y" floating, with the other 3 wires tied to the FDAI inputs. The reference will be just a single winding between the output driver and ground.One reason I never found this part on my own, was because it seems like Digikey and Analog Devices really like to return some VERY spendy chips when you specifically search for a multiplying DAC. You're guaranteed an adjustable voltage reference if you get one, but lots of chips can do the same, without costing $10 or more per DAC channel. Imagine, a company making it easier to find higher priced products...Turns out, external voltage reference input wasn't a search criteria that was easy to sort for.Thanks to someone else's knowledge, I was led to the MCP4922. Does what I need, since it has the all important external voltage reference input, handles a pair of 12-bit DAC channels per chip, and for just $2.76 a chip! Noice!To top it all off, I have9074HC4066 quad bilateral switcheson hand, 20 DIP and 70 in a variety of SOIC and SOP packages. I have no worries about dealing with the analog switches to select whether to reference the inverted or non-inverted reference sine. I think I'll have enough parts!Between the DACs having sufficient resolution to handle fractional degree increments of the navball, the sine being generated in hardware, the polarity flip being easily handled by the arduino using the analog switches and a pair of op-amps... I should have FAR less to process inside the Arduino, and I should be able to send out the data at a more than reasonable rate!Even if I have a PEAK of 60 update frames per second, then I need to send 60 x 9 SPI transmits each second. That's only 540 transmissions per second! I'll need 5 Chip select lines, plus the SPI bus connections, and a single digital out to update all the DACs to their newly updated values. I'll also have an incoming serial bus that it will be watched for frame updates.Again, I apologize if anything seems out of place, or if I explain things you guys already know. This post was a mix of two pieced together posts from a forum, plus some original typing. If I left any of thoseCSI: Whereverstyle "explain the crap real professionals would already know for the audience" moments, it's because I originally put it in for some of the people on the other forum, where not all the people are as electronically gifted as the people here.Anyway, it's also 1:25 AM... Going to bed now!

author: richfiles
author_rank: Regular Contributor
timestamp: October 21, 2015, 08:44:02 am
content: This is basically the simple schematic of what i'm trying to do.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 21, 2015, 12:38:27 pm
content: If the requirements are too much for a single microcontroller (Arduino or whatever), then why not simply use "distributed processing" where each channel has its own micro generating the three phase signals, but under the control of the master, and operating from the same reference phase, etc. Arduino-like clone boards extraordinarily cheap on Ebay, down into the $1-2 range. Perhaps even a little board that does 3-phase generation might even be a "niche product" that you could sell to others.This guy simply uses 8-bit R/2R resistor ladders as D/A conversion.http://www.instructables.com/id/3-phase-sine-wave-generator-based-on-Arduino-Due/?ALLSTEPS

author: richfiles
author_rank: Regular Contributor
timestamp: October 21, 2015, 01:50:51 pm
content: With waveform synthesis, I need to keep all three axes synchronized with the reference, so then I have the device watching a serial bus for incoming updates, and trying to maintain timing with a 400 Hz input... Not to mention, do I have one arduino work extra to generate that? It'd be a non symmetrical work load then. or one arduino just to do reference? The others still have to watch for serial input, and still have the added effort of watching an input that can "scan" the reference.The simplest option that I can see, is the hardware solution, as it eliminates all this software complexity and multiple controllers with a single, simple solution. It took $13.80 to buy the 5 DAC chips. The 74HC4066 would have cost me about $2.50 for all the chips I needed. I'll need a dual op-amp chip, which I'm sure is under half a buck. The output stage would have been the same as with the software only plan, so I'd say this new design is actually already coming out ahead of the old software only design, cause I spent $30 on those 10 DACs I'd ordered before! It's also 540 data transmissions per second + watching one serial input for data with this hardware design, vs 307200 data transmissions per second plus watching a serial bus, plus staying synchronized with an input that has to be sampled fast enough to capture 102400 updates per second... If I use a wave resolution of 256 slices per cycle. Wouldn't you need a better sample rate than that to read it properly?There's the argument of cutting back on the timebase resolution. Sure, I can add filters and possibly even do a square wave, but I wanna make sure that no unnecessary square wave harmonics are passing through... An FDAI CAN get loud, and pass those harmonics through as sound! Just the 400 Hz sine might drive some people nuts! I worked with it for years though.

author: Dr pepper
author_rank: Newbie
timestamp: March 10, 2016, 12:14:58 am
content: I know this thread has gone quiet, however I'm interested to know if the o/p has had any success.I have messed with synchro's a few times, 3 phase and 6 phase, dc and 110v ac, my code and hardware is much simpler, usually just a L293 H bridge and a transformer for the ac ones, reading th eposition from a transmitter is a little more complex.Instead of complicated maths calculations I just move the synchro a very small step at a time then keep track of the position using a register.Heres one of my vids, this is a 6 phase, check my channel there are others:

author: Dr pepper
author_rank: Newbie
timestamp: March 12, 2016, 08:30:16 am
content: Heres a 110v 3 phase:

author: Rerouter
author_rank: Super Contributor
timestamp: March 12, 2016, 08:56:41 am
content: as for the I2C stuff, if the op is still ever around, i would suggest bitbanging the I2C, this way you can write all the data pins at the same time by writing to the port direction registers,

author: richfiles
author_rank: Regular Contributor
timestamp: April 12, 2016, 07:06:32 am
content: This is what I've been doing for the last few months...I'm still around. I set this project aside for a couple months to design and build a mechanical keyboard. Actually, I had a LOT of frustrations happen one after another... First the cheap Chinese LED display drivers and display modules that I had ordered for the project lit up the wrong color! I ordered green LED versions. That cheap Chinese seller actually tried to weasel out of it by claiming he meant the PCB was green!After that, I got ebay to force a partial refund (I explained the driver boards were fine, and socketed, so I could replace just the LEDs). That partial refund went to buying green LED displays to plug into the driver boards... Those cheap Chinese replacements had a worse than 50% fail rate!?!After that, I did the math and learned that I2C can't even support the data rate required for the project, making the $40+ DAC/Amp board I built a paperweight.I still never found a use for it.In the end, all the hype and talk about Kerbal Space Program 1.1 led me to decide to wait for 1.1 to come out, and to wait to see how the KSP Serial IO plugin develops under the new version. in the meantime, I had my hand at building a custom mechanical keyboard. It's a modified 75% layout (I call it 75%+1). It's an 88 key layout that can be populated using standard ANSI key cap sizes. It Uses a Teensy 2.0 controller, has uniform under key lighting (amber), has a blue anodized aluminum switch plate, and Gateron MX Blue switches, with the top switch housings dyed blue. It also has a magnetic connector on the side that allows an external number pad to be magnetically attached, as desired. I have not made the number pad yet.Being mostly done with the keyboard (Still programming it), and with the release of KSP 1.1 on the horizon (it's currently in open pre-release beta), I expect to soon return to building the Kerbal controller. When that occurs, I will most certainly continue this thread... The sad thing, i sI was totally looking at Tachtronic synchro control transformers on ebay... Part of me was still tempted to do a controller involving something I actually once built... But I like the electronic controller better.So yeah... The attached images are what i've been doing for the past few months, instead of this. I'm quite proud of the wire lacing that I did! I think wire lacing is a lost art that deserves some appreciation. I actually used unflavored waxed dental floss as my lacing cord. I did some lacing early on, but all the wiring from the teensy... that's one single piece of cord... And a LOT of pulling cord through loops to knot it!

author: SeanB
author_rank: Super Contributor
timestamp: April 12, 2016, 07:18:56 pm
content: That is one nice looking piece of lacing, and dental floss works well there, the real stuff just is thicker waxed floss. Did you use a curved needle to get all that floss into place.

author: richfiles
author_rank: Regular Contributor
timestamp: April 13, 2016, 02:09:02 am
content: I used tweezers, fingers, and the right tongue angle.

author: sbennett1298
author_rank: Contributor
timestamp: November 26, 2016, 09:34:55 pm
content: richfiles,How far did you get emulating synchs with the arduino?I am trying to do the same thing and I have some ideas.I want to drive an attitude indicator. Very similar to what you were attempting.Let's exchange some ideas.Here is what I am thinking.Build a 400hz oscillator and run that to an inverting op amp.Use a SPDT relay to select 0 phase or 180 degree phase.The arduino PWM outputs be could converted to true analog voltages using simple RC filter and that could drive a voltage controlled amp to get the desired amplitude.Sound plausible? I considered digital pots but the arduino can only control two and I need three.I am just starting and have not attempted any of this yet.-Steve

author: Rerouter
author_rank: Super Contributor
timestamp: November 26, 2016, 10:02:45 pm
content: He mentioned that there where 3 clocks, a 0 degree, a 120 degree and a 240 degree, as its only 400Hz, i would think something like 3x AD9837 for the reference clocks, and just initialize them with delays to match the phase shift, all running off the one clock.As for 9 or more amplitude modulated signals, use a digipot per channel on the AD9837 outputs, then AC couple it and amplify it to the voltage required,The way you only need the arduino updating the digipots, everything else is already taken care of.If needed you can add some filtering to the outputs to clean up the 10bit steps from the sine outputs,

author: sbennett1298
author_rank: Contributor
timestamp: November 27, 2016, 02:02:43 am
content: Rerouter,There is no phase shift as you would see in three phase power.The three coils in a synchro stator are in phase or flipped 180. Only the amplitudes are different.This is because the rotor that provides the excitation voltage is single phase.The rotation angle of the rotor determines the amplitude and polarity of the stator coils but there is no phase shift.-Steve

author: richfiles
author_rank: Regular Contributor
timestamp: November 27, 2016, 05:36:18 am
content: Rerouter, I'll be using a few 12-bit MCP4922 DACs. I can feed the sine wave into the reference, so the DAC's output level will scale the reference input. It's all about amplitude and polarity. As for my sine source, I recently dug up an old digital sine wave generator from an old California Instruments Invertron AC power inverter. It's certainly old, but it fits the retro feel of my instrument panel. My only regret, I simply don't have any room left for it on the main panel... I'm gonna have to bury it inside the unit. It's not like I need to change any of the controls anyway. Just a shame to hide vintage equipment.

author: Rerouter
author_rank: Super Contributor
timestamp: November 27, 2016, 07:18:32 am
content: Sorry, my understanding of these devices is rather poor,I would avoid voltage controlled amplifiers if possible, just because they appear quite expensive per unit.As for inverting the waveform, then instead you could use an ad9850, it has complimentary sine outputs, which you could use simple and dirt cheap analog switches to select between per channel

author: richfiles
author_rank: Regular Contributor
timestamp: November 27, 2016, 11:08:08 am
content: I actually have a "crude schematic"... more of a block diagram, and all the part numbers that I plan to use on the second page of this thread. To recap:MCP4922 12-bit Dual DAC with Voltage Reference (5 on hand)74HC4066 Quad Bilateral Analog Switch (90 on hand)LM675 Power Op-Amp (16 on hand)California Instruments 850T Precision Oscillator (salvaged from equipment from previous employer)As I said, I got the parts, and I have a proposed "layout" for the whole thing. Frustration from problems with the previous build attempt, switching over to working on my mechanical keyboard, and then a long stretch of work has kept me from sitting down and getting back into this. Maybe winter will get me back into it. Haha!Updated the crude schematic to show the correct output voltages, and reference the 850T sine generator. I'm going over the documentation for the 850T, and it may actually have an inverted output built in. I'll have to test that out to be 100% sure, but I may not even need the op-amps to invert the sine wave.

author: Rerouter
author_rank: Super Contributor
timestamp: November 27, 2016, 07:36:20 pm
content: I think you will need ac coupling caps either before or after the final output buffer to the transformer. The current needs to reverse each waveform.

author: richfiles
author_rank: Regular Contributor
timestamp: November 28, 2016, 01:05:21 am
content: Quote from: Rerouter on November 27, 2016, 07:36:20 pmAs I mentioned before, it's effectively a block diagram, not anactualschematic. It's a "crude" representation. I'll certainly need to do the same for the output of the 850T, as I'll have a 0 crossing waveform being fed into a 0-5v DAC... Ah!, and I see that's something I missed when I altered the diagram. I should have changed the 0-5 on the 850T to a +/-2.5v AC out.

author: sbennett1298
author_rank: Contributor
timestamp: November 28, 2016, 10:13:31 pm
content: Richfiles,I'm a bit confused by the way you are using the DAC.What does the VREF input do?It would make sense to me if the output of the DAC is multiplied by VREF.But I suspect it is added.So in other words it looks to me like the output is going to be a 5V sine wave riding on top of the DC value sent to the DAC via the SPI interface.The amplitude of the sine will never change. You are only changing a DC offset.I think instead of a DAC you want a digital potentiometer.I admit I am not familiar with this device or the purpose of VREF.-Steve

author: daveatol
author_rank: Regular Contributor
timestamp: November 28, 2016, 11:29:43 pm
content: Quote from: sbennett1298 on November 28, 2016, 10:13:31 pmSee section 6.9 ofhttp://ww1.microchip.com/downloads/en/DeviceDoc/21897a.pdfThe VREF is the FSR of the DAC.

author: sbennett1298
author_rank: Contributor
timestamp: November 29, 2016, 04:02:28 am
content: After some more reading I found this formula.Vout=Vref*(2^n -1)/(2^n) to get the maximum value.So yea it makes sense. The device is multiplying the ratio of (digital value)/(max digital value) by Vref.Can Vref take negative values?If your oscillator is crossing zero that has me a little confused.Still not sure I understand the transformers shown on the output.Are the transformers part of your circuit or do they just simulate a load similar to the actual aircraft instrument?-Steve

author: salbayeng
author_rank: Frequent Contributor
timestamp: November 29, 2016, 04:51:55 am
content: Hi Not sure if anyone mentioned it yet,But you don't need 3 outputs from your MCU to make the three synchro amplitudes ( or even the 3 x 400Hz signals)You only need 2 signals sin and cos, these are used in "sincos resolvers" a two phase relative of the synchro.So you just generate a 0deg signal and the 90deg signal, and from these two signals, using summing resistors and opamps, make a 120degree and 240 degree signal,Something like this 120deg = 2/3*90deg -1/3*0deg , and 240deg=-2/3*90deg -1/3*0deg(The 1/3 and 2/3 aren't exact it's some trigonometric number I'm too lazy to look up)

author: sbennett1298
author_rank: Contributor
timestamp: November 29, 2016, 02:58:41 pm
content: Salbayeng,There are some aircraft indicators that use resolvers (sin/cos) but this one uses a synchro. Resolvers and synchros are two different animals.-Steve

author: rstofer
author_rank: Super Contributor
timestamp: November 29, 2016, 03:23:59 pm
content: When this same subject came up last week, I wandered around looking for 3 phase circuits. I found one that used some op amps to convert from sin()-cos() quadrature signals to 3 phase but I don't see it this morning.However, TI has an app note on generating low frequency 3 phase signals:http://www.ti.com/lit/an/sbfa013/sbfa013.pdfSo, you generate the signals with the UAF42 and then use op amps to modulate the voltage (and boot it).I don't know if the TI approach will work any better than anything else but at least the chips are in stock at Digikey

author: richfiles
author_rank: Regular Contributor
timestamp: December 02, 2016, 06:37:06 am
content: Quote from: sbennett1298 on November 29, 2016, 04:02:28 amIt will be decoupled from the rest of the circuit. Again... The schematic is a crude functional layout, not even remotely close to an actual finalized part by part schematic.Quote from: sbennett1298 on November 29, 2016, 04:02:28 amThe transformers are there to both step up the voltage and to float the signals. The normal signal source for the FDAI would be three synchro control transformers. None of these signals are tied to a reference, so I'm floating them. The signals are 28 volts VAC, and the reference is 115 VAC. Having talked to a few people who have built simulators before, even if you under-volt the whole system, you still need around 70 VAC even to get it to run. I'd forgotten i bought them, but I got some 18 watt modular audio drivers from a surplus supplier. I realized I could drive those with some current behind them, and step that up to the required 115 volts, so there's enough power to drive the unit. All operating power is derived from he 115 VAC, 400 Hz reference signal. Here in the US, our mains is 120 volts, so I can pretty much adapt nearly any mains transformer as my step up by just using it in reverse... I'll feed power into the secondary. I just need to find a beefy one that has a sufficiently high enough current secondary to power the FDAI.I honestly do not know if the signals need to be floated or not, but I'm not gonna take any chances... I paid WAY too much for this FDAI unit... I'm gonna play things by the book when I power it up. I won't have the cash to replace this thing if I manage to screw it up, so if the original application floats the signal inputs, I'm floating my signal inputs.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 02, 2016, 09:18:18 am
content: Hi Rich.You only need two channels ,"North" and "East" and then transform these to UVW.So If I generate 100% of north and 0% of east, the compass card will point North, I need 100% in the U winding and zero in the other two.If I want to point at 120degrees around (South of East) then I put -50% in North and 86.6% in East.(or something like that) Read the maths about page 6 of this:http://www.ddc-web.com/documents/synhdbk.pdfSee attached schematic that replaces , say, your yaw channel.Its just a Scott T transformer, it works the same with rotating 3 phase power (used in motors) , as well as single phase with 3 amplitudes.Here's a way of generating the two 400Hz waveforms (N and E) and combining them.You can do the conversion with resistors and opamps, if you would prefer to use transformers with the same turns ratio.Note that speaker transformers for use in PA systems, have multiple taps, so you should fins something close enough to 0.866 turns ratio, (even if this is not exact you can run a look up table for calibration)So your software would be passed theta, and you output sin(theta) on North and cos(theta) on east.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 02, 2016, 01:22:18 pm
content: On eapproach you should consider:Look at multiplying DACs like DAC8802http://www.ti.com/lit/ds/symlink/dac8802.pdfYou can feed a 400Hz sinewave into REFA and REFB , then the amplitude of the sinewave generated by the dac is just the value you enter in the DAC, so 16383 = full scale sine wave, 8096=half scale , 0 = zero.Its a dual DAC so you can get "north" and "east" signals out, then mix them (as per my earlier post) to make UVW.This only gets you signals that are in-phase with your reference. To get full 4 quadrant operation, you need to subtract half the reference voltage , this can be done with a single resistor into your summing amp.You only need to update the DAC's as fast as your airdata signals change, so maybe 100Hz at most.Note you can also use sigma/delta dithering to increase your effective resolution. (but not the accuracy).

author: richfiles
author_rank: Regular Contributor
timestamp: December 02, 2016, 11:33:30 pm
content: The DACs I have already support what you describe, and in fact, that's already what I am doing. I'm feeding my sine wave into the reference, and scaling it with the DAC value. The datasheet specifically addresses the use of that part as a multiplying DAC. The DACs I have are even dual DACs.I'll probably stick to 3 phases though, since I have enough DACs for it, I (more or less) know how to do the conversion from the Kerbal Space Program data to the three phase data, and my transformers are not center tap transformers. I'd have to get all new ones if I switched to your setup. I have more than enough power op-amps and speaker driver modules to build this. It's gonna be easier for me to just add the three extra power drivers, than to source new transformers and build the extra op amp circuits before the power drivers.Very interesting design though. I might have opted for it instead, had I seen and comprehended it back when I was starting.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 03, 2016, 02:11:17 am
content: Oops my apologies, I was familiar with the MCP4822 (Internal reference, I2C) and I thought the MCP49 series wasjustan interface swap to SPI.If I re-read your schematic it makes more sense now. It seems a perfectly sensible approach.I've got a handful of synchro type flight indicators myself, and was contemplating using a 3 "phase" Hbridge to drive the synchros, I've made a similar inverter to drive a BLDC servo motor. So I'm following your project with interest.Where do you get the mating connectors to plug into the instruments?, they all seem to be non-standard variants of MILSPEC connectors.There is another alternative two transformer approach, "grounded delta" , which uses two transformers with equal ratios driving U and V , while W is grounded, might be worth a look. The drawback is you need double the voltage swing (i.e. you need +/-100v to get 100v across any winding, as opposed to +/-50v to get 100v across any winding).

author: richfiles
author_rank: Regular Contributor
timestamp: December 03, 2016, 07:37:01 am
content: While I haven't verified it for quality of connection yet, It seemed some Radio Shack DB-25 sockets (the type you crimp to a wire then insert into the plastic housing) would fit the physical pin.My plan was to insert a paper "plug" into the connector, line it with a mold release, and then just pot the pins into the connector... and hope it'll come back out. I'll need to make sure my release is able to be easily cleaned up.Short version,I'm making the connector,unless I actually find one. I have a box of random mil spec connectors from my old job, though i doubt I have a match.For securing it, I suspect I might be able to salvage at the very least the ring from one of those connectors. There has to be one of those that at least fits from that box.**EDIT**I found the correct matching connector and bought it off ebay.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 03, 2016, 07:57:39 am
content: Ok, I use a similar method with hot melt glue, it's quicker and you can rework it easily. (but too soft for a locking ring to work properly)The Dtype connector was originally MILSPEC, so you can use those 1.0mm pins/sockets (same as a milspec 20 contact)The 1.6mm pins and sockets (milspec 16g ) are also fairly easy to find in commercial parts.The bigger 12g pin/sockets are more difficult to source 2 or 2.2mm??

author: sbennett1298
author_rank: Contributor
timestamp: December 05, 2016, 11:37:54 pm
content: I had the same idea of using Radio Shack DB-25 sockets. I was thinking use shrink wrap on each individual socket before potting to help keepthe potting from getting into the sockets. It might be worthwhile to make a jig for potting instead of risking the instrument to do it in place.I was also thinking that maybe instead of potting I could machine something out of hard plastic.It would be great to find affordable milspec connectors that fit but so far no luck on that. I did find a data sheet for my connector.Mine takes the rectangular MC28748http://www.vishay.com/docs/36009/mc28748.pdf-Steve

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 06, 2016, 12:59:37 am
content: Steve ,These are 22g 0.76mm contacts , you need to use the "high density" D types, commercially these would be in the 15pin DB-type videoconnectors (3 rows). Its correctly called a DE15 connector (but may be sold as DB15)The normal Dtypes are 1.0mm pinsSome of the commercial grade 2.54mm pitch headers/receptacle also use a 30mil pin (but most are square)Heatshrink would be a good idea. Squirt some Silicone grease (any grease really) in with a syringe after shrinking.Other useful things :Wax, you can melt and pour into an existing male plug to ensure the potting compound doesn't run around the pins. Melt out later.Plasticine for moulding with (it gets a lot thinner when heated too)Poster adhesive (BluTak)Latex masking compound, shrinks on drying, withstands solder temperature, and pulled off like a rubber band.Silastic RTV making moulds etc (This cures a lot faster if left in a warmish oven (60-70C) with a pan of water) (as a substitute for two part silicone mould making compounds), It's thicker, so it stays put.Hot melt glue.

author: richfiles
author_rank: Regular Contributor
timestamp: December 06, 2016, 05:46:14 am
content: I have to admit... Using heatshrink around each pin before potting to prevent contamination makesa lotof sense... And it never occurred to me...Good call!Liking the good ideas here! Thanks!

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 06, 2016, 07:32:33 am
content: Particularly with sockets you need to allow wriggle room. Some thin silicone rubber tube may be useful too.5ml syringes with glue nozzles are useful too. (most of those toothpaste tube type greases and RTV's will fit in the back of a 5ml syringe (pull plunger out first))e.g. kits like thesehttp://www.ebay.com.au/itm/SMD-PCB-Solder-Paste-Adhesive-Glue-Liquid-Injection-Dispenser-Dispensing-Needle-/131046058700?hash=item1e82f42acc:g:WQMAAOSwd4tTs31j(I've actually got a real kit of these $$$$ but for disposable use the cheapies are adequate.)For two pack adhesives I find polyurethane is good, it sets fast, very strong, but is still a bit flexible. Huntsmen chemicals(USA) make "double bubble" sachets

author: sbennett1298
author_rank: Contributor
timestamp: December 06, 2016, 07:03:47 pm
content: I also thought about just using a wire wrap tool to wrap leads directly to the male pins but the only reason I didn't was because the pins were too thick for the wire wrapping tool I have. If there is a need to have a removable plug you could put a plug on the wire wrap leads and secure the wires with some sort of strain relief.I wonder if they make a wire wrapping tool that will fit over those pins?It wouldn't be hard to make one.-Steve

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 06, 2016, 09:44:32 pm
content: Hi,I've just tried using a wire-wrap tool on a DE15 connector, and this seemed to work OK, on the 0.76mm (30mil) diameter pins.(I thought not having round pins would be a problem, you are not going to get the same "gas tight" effect as with square pins, and wire might slip)The 24mil square wire wrap post is 32mil on diagonal.Are you sure you have 0.76mm diameter pins?

author: sbennett1298
author_rank: Contributor
timestamp: December 07, 2016, 12:19:55 am
content: I have not measured my pins yet but I think they are 30mil.The wire wrapping tool I have is for the really fine blue wire they sell at Radio Shack.It is fine as frogs hair. Maybe 15mil?I must have another wire wrap tool around here someplace because I'm sure I had one that worked on the square pins of DIP sockets.-Steve

author: CM800
author_rank: Frequent Contributor
timestamp: December 07, 2016, 12:47:54 am
content: Quote from: sbennett1298 on December 07, 2016, 12:19:55 amHave you considered just buying the suitable connector?It's usually not hard to find it with some intuition and an Amphanol datasheet / product guide. I've done it before.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 07, 2016, 12:55:44 am
content: Ok I have a standard size blue handled tool here, from "OK Industries" part "WSU 30-M" I guess thats 30milhttp://au.mouser.com/ProductDetail/Jonard-Industries/WSU-30M/?qs=%2fha2pyFadujGQ3IVLLGAf6fxCcINAoooqG%252bqR7M5gg4%3dOoops the data sheet says "30" is for 30awgAnd another clone of that from "O.K. Industries Inc" part "WSU-30M" and "made in China" and also "made in P.R.C" (to avoid confusion?)Never seen a smaller one, I have seen a larger one for 40mil or 60mil? power supply pins maybe this onehttp://au.mouser.com/ProductDetail/Jonard-Industries/WSU-2224/?qs=%2fha2pyFadujigxftUDcPEolmMNeZo5RHS9DIzT4xDrQ%3dI've got one of thesehttps://www.jonard.com/Products/ProductDetail.aspx?p={EFAF6BC9-4E97-4AE3-84F5-FBD8F86FE172}red/white/blue wire + stripper + cutter , it get's used a lot for development and board mods (no actual wire-wrapping though), it's even better if you tape a small length of angle to it and attach a binder clip, then you can use as a length gage.

author: sbennett1298
author_rank: Contributor
timestamp: December 07, 2016, 02:56:44 am
content: I would prefer to buy a connector if the price were right.I have just not been able to find one. The ones I did find were either too expensive or the web site said "request a quote".Well "request a quote" sounds like it would either be expensive or have a large minimum order so I have not bothered with it.Since I am just tinkering around I could not pay more than $15.There seems to be a bewildering array of variations.Most I have seen had threaded guide posts. Mine are not threaded.My guide posts are male on one end female on the other end. non-threaded.Total of 14 pins if I remember.-Steve

author: CM800
author_rank: Frequent Contributor
timestamp: December 07, 2016, 06:43:03 pm
content: Quote from: sbennett1298 on December 07, 2016, 02:56:44 amFrom your image, I can say this is the exact connector you want:PT06A-18-32SIf you find one, make sure if there are any letters after S it doesn't have a W,Z, Y or Z as they are shell rotation / key optionsPT06A-18-32S-SR would be the best one as it has strain relief added.http://uk.farnell.com/amphenol/pt06a18-32s/connector-circular-size-18-3way/dp/1482714http://www.mouser.co.uk/ProductDetail/Amphenol-Industrial/PT06A-18-32S-SR/?qs=lIrZrna%2fvtCpLVeX8IKatw==Would be the ones you want.It's really quite quick to find the exact connector you need, just from looking at it and the Millspec datasheet for it's series.(Page 25)http://www.farnell.com/datasheets/2167054.pdf?_ga=1.120726091.214707435.1448714711

author: sbennett1298
author_rank: Contributor
timestamp: December 07, 2016, 07:42:54 pm
content: CM800,The instrument I have uses a rectangular connector. MS24009G.http://everyspec.com/MS-Specs/MS2/MS24000-MS24999/MS24009G_37724/-Steve

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 08, 2016, 03:12:43 am
content: Getting back to the original poster (richfiles) round connector.This looks like a standard milspec connector (as expected from s simulator, real aircraft instruments have different polarisations to standard connectors)The contact arrangement with 4 in the middle and 2 more rings of contacts is quite common it's known as "18-32"You need sockets in yours so its now "18-32S"Normally you would want a straight plug so the beginning of the part number will be "MS3116" or "KPT06"(right angle is MS3118 or KPT08) other manufacturers may have different part numbers but will have a 6 in it.So you are looking for a xxxxx6x1832Sxx or xxxxx6x18-32Sxx where the xx can be various numbers or letters , the letters on the end are environmental codes, take any of these. (and also xxxxx8x1832 etc)If you searching on distributors or even ebay, search for "18-32S connector" or "1832S connector"some hitshttp://au.mouser.com/Connectors/MIL-Spec-MIL-Type/Circular-MIL-Spec-Connectors/Circular-MIL-Spec-Connector/_/N-cigvbZscv7?P=1yzv62lZ1yzv7x1&FS=True&Ns=Pricing|0http://www.ebay.com.au/itm/272327980873Note you sometimes don't get the backshell with certain part numbers.

author: richfiles
author_rank: Regular Contributor
timestamp: December 08, 2016, 02:33:54 pm
content: Well... Turns out you can find the 18-32 connectors for way cheaper on ebay! I was going to use individual sockets, and then pot it, but seeing that... I may as well get the proper connector. I've not found an 18-32 in my "Big-Box-O'-Mil" connectors yet, but I suppose I could give it another quick search, just incase. I'd looked at the price at Digikey before, but it turns out they were one of the more expensive places to get them from, so I kinda quit looking once I'd leaned D-Sub pins fit the pins.Ebay definitely seems to be the cheapest way to get this.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 08, 2016, 11:51:11 pm
content: Given that most buyers want fully traceable parts, there's not a big market demand for used or NOS MILSPEC connectors, and the average guy stumbling across some thinks he will make a killing on Ebay, only to find there aren't that many buyers, so has to sell them pretty cheap.In the US you should be able to find some enterprising individual who has a 55gal drum of old harnesses from a boneyard.Even buying new there are specialist MILSPEC connector suppliers out there, with good prices.We had a big box of MILPSEC connectors at a prior workplace, we called it our garden gnome collection, they were green, and decorative ,and that was about it, in a box of 100 or so you could never find the one you wanted.

author: CM800
author_rank: Frequent Contributor
timestamp: December 09, 2016, 01:01:12 am
content: Quote from: richfiles on December 08, 2016, 02:33:54 pmJust make sure that the 18-32 doesn't have any key angling + is a receptical. The part number you'd be looking for should resemble the one I posted further up.

author: richfiles
author_rank: Regular Contributor
timestamp: December 09, 2016, 02:27:21 am
content: QuoteHey! I have that very same box too!Fortunately, I have a bunch of mated pairs in the box, so I actually have SOME use for it.As for what I've found online, I already have found ones that match my keyway and everything.

author: sbennett1298
author_rank: Contributor
timestamp: December 12, 2016, 10:01:28 pm
content: I have a helicopter I picked up at radio shack that is controlled by an app on an iPhone.In one mode of operation you use the accelorometers inside the phone and you tilt the phone to steer the copter.I think it would be neat to control one of these nav balls with an iPhone app.I guess you'd need a Bluetooth shield.-Steve

author: sbennett1298
author_rank: Contributor
timestamp: December 14, 2016, 06:31:56 pm
content: Well after a brief look at iPhone development I can rule that out. They charge you for the privilege of write code and loading it to your own phone.What a crock.Maybe Android is more developer friendly?-Steve

author: mapadon
author_rank: Newbie
timestamp: January 15, 2018, 09:12:25 am
content: Hi to everybody,I´m doing a project similar to this one, but I´m stuck in some points that maybe you can help:-Is there any way to synchronize with the 400hz referece? I have an external 400Hz supply Behlman and I think that there´s a way to use its sine wave.-Why are the 74HC4066 needed? The carrier is the 400Hz sine wave, right? And the 120º shif must be implementd in the modulator through the DAC.-Concerning the transformers, do you have any reference? The only 1:1 that I can find are pulse transformers, and I´m not sure they could be suitable for thise design.Thanks in advance

author: sbennett1298
author_rank: Contributor
timestamp: April 15, 2018, 05:00:31 am
content: richfiles,I recently started thinking about this again. How to make an AC sine wave vary from full amplitude to zero and then to inverted full amplitude?How about a cross fader circuit like a music disc jokey uses to fade from one turn table to the other? Fade from plus 400hz to inverted 400hzThere has got to be a digitally controlled way to do this.One way is voltage controlled amps driven by pwm.Also I am thinking transformers are not needed in your design.Can't you just used a decoupling capacitor to send the signal to an audio amp that has dual power plus and minus.It just boils down to mixing two sine waves together where one is an inverted copy of the other and scaling them to get the desired result.That can't be all that difficult. I know this is an old tread. Did you ever get anything to work?-sbennett1298

author: richfiles
author_rank: Regular Contributor
timestamp: July 25, 2019, 01:10:30 pm
content: Trying to get back onto this project. Major changes since I last worked on it. Job change has left me with more free time. I finally learned how to use KiCAD. Considering the project will use three axes, and board vendors (like OSH Park) often have a three PCB prototyping offer, I've realized when I do the design, I need only design the circuit for a single axis, with input from the reference circuit. I can then have the board manufactured, and then populate components for all three axes on all three boards, but only populate the circuitry for the reference on a single board. I will tap the one board's reference signal and share it between the other two, which will be partially unpopulated. Since the reference will likely be externally provided, I can more or less just have the phase inversion and power driver circuits, and that ought to cover it.Now I gotta figure out the details of the circuit. I'm still too paranoid about blowing up anything in the FDAI, since it was costly enough to get it. I want every aspect of driving it to be by the books. I need more than a rough block diagram now. For now though, just the small update. I'm alive, I learned KiCAD. Still need to learn how to really code on the Arduino. What little practice I had playing around with it was ages ago, and I need to get hardware built, so i can actually experiment now.

author: jmpowell
author_rank: Newbie
timestamp: August 11, 2019, 09:44:22 pm
content: I've built a couple of digital-to-synchro (DTS) converters. My approaches were different than the route you've taken, but perhaps they will offer some ideas you might find useful.The definition of the synchro stator terminal voltages is given as differences between stator phases. There is no reference to "ground". This is by design. Think of the stator voltages as a three phase differential signal with strong immunity to ground loop noise. That said, you're free to define the voltages on the stator phase with respect to ground as you please as long as the voltage differences between phases still meets the synchro definition, and you are willing to accept any impact of electrical noise on the ground. (Noise turns out to be not that big a deal in many applications.) You might, for example, define the voltage of S1 to be zero. Now you only have two stator voltages to generate: S2 and S3. You can still isolate from ground using a pair of transformers if this is needed.Both DTS converters I built take this general approach.DTS v1 takes a sample of the 400 Hz power and passes it through a 12-bit, four quadrant multiplying DAC. (An LTC1590, in this case) The DAC output goes to an opamp with selectable gains of +1 and -1. This, in turn, goes to a power amp (LM1875) which is the DTS output. Peak output voltage is only about 12 volts.11.8 volts peak for synchro stator voltages is common. 115 volts and 28 volts are common synchro rotor voltages. An ADI with internal servo electronics may take 115VAC/400Hz on the connector to power it, but use only 11.8V on the stator control inputs. This was the kind I was targeting with my designs.DTS v1 utilizes a PIC16F648A to manage communication with the host and load the MDACs. All the heavy lifting is left to the host.DTS v2 came about from a desire to reduce costs and to get away from the switchable gain opamp. Effectively, this "sign bit" becomes the 13th bit in controlling amplitude. It needs to be really accurate to match the accuracy of the 12 bit MDACs. I also wanted a more versatile converter, something that could be used to drive a synchro receiver style engine gauge, as well as, act synchronously with other converters to drive the multiple inputs of an ADI.DTS v2 generates a pair of controlled amplitude, 400Hz sines alone with a signal that can be used to make constant amplitude 400Hz power. Further, the converter accepts a 400Hz input that it will synchronize with. An individual DTS v2 with an external power amplifier can generate all that's needed to drive a single synchro-receiver style gauge. A group of DTS v2 converters can synchronize with an external 400Hz power source and drive an instrument like an ADI.At the center is a PIC16F648A generating a pair of "modified sine waves". A modified sine wave is a square wave with some extra time spent at zero when making the transition from minimum value to maximum, and visa versa. If the time at zero is properly chosen, the third harmonic is canceled out. It's really easy to filter and be left with a very pretty sine wave. DTS v2 uses a single quad opamp and a (very small) handful of SMD components to greatly overkill the filtering of both channels. Amplitude is controlled by the min and max values loaded into the DACs. These don't need to be MDACs, so they're cheaper. While technically the PIC is generating the modified sine wave, all it's doing is listening to its internal timers and loading values into the DACs a few times per cycle. Once again, all the heavy lifting of calculating those values is left to the host. The DAC outputs go to power amplifiers. The LM1875s have gone up in cost. TDA2030ALs are less than a dollar from Tayda Electronics and should do as well. There are some pictures of the DTS v2 PCB along with waveforms on my sitewww.mikesflightdeck.comScroll down to July 2015. (There's also some synchro related material in the Oct 2006 portion of "old news" on the site.)DTS v2 was not fully debugged/tested though it does appear to generate proper signals and sync with an external 400Hz reference. A remaining item is the need to accommodate the phase shift through the filters so that the stator signals are properly in phase with the reference.

author: sbennett1298
author_rank: Contributor
timestamp: August 23, 2019, 03:48:20 pm
content: Richfiles,Did you ever get this working? I just found out there is an Arduino shield called 1Sheeld+ that lets your Arduino use any sensor on your Android via Bluetooth!Imaging being able to control your navball by tilting your phone! If you get the plus version it will also work on iOS. -sbennett1298

author: rstofer
author_rank: Super Contributor
timestamp: August 23, 2019, 04:57:41 pm
content: Having read through this thread, I still have no idea what needs to be generated. There appear to be 3 in-phase 400 Hz signals of individually varying amplitude plus (maybe) a reference signal of constant amplitude but also in-phase. Am I even close?Well, assuming I am, why not use analog multipliers. Generate the reference waveform and smooth it as much as necessary and then feed it into 3 analog multipliers. Drive the X with the signal and the Y with the amplitude. Now, the amplitude doesn't change all that fast so any decent 16 bit DAC will keep up and have quite a bit of resolution. We're dealing with a qualitative display, not quantitative. We don't need 10 decimal digits.All the Arduino would have to do is grab the simulator data, figure out the 3 amplitudes and update the DAC - at the frame rate, not at 400 Hz. And not times 10...Some timer function in the Arduino could create the 400 Hz square wave output which would be filtered substantially.Electrically, the output of the analog multipliers would be signals with amplitudes between 0 and +- 10V. Inversion is possible with an Op Amp providing the offset ahead of the multiplier. The multiplier DAC would output 0..10V and the op amp would change it to -5..+5 or something like that.The output of the multipliers is an amplitude modulated 400 Hz signal. It would need to run through some kind of driver to drive the transformers that drive the FADI.I think... I could be way off!If the waveforms need to be spread apart by 120 degrees then things get more difficult. But not that much! Yes, the Arduino has to generate 4 waveforms (x,y,z,ref) but they are strictly correlated in time. In other words, when you compute an index into the lookup table, the other indices are a fixed distance further along in the table. In fact, you should never have to compute ANY index because you step through the table in discrete steps - one step per iteration. What you don't want to do is use floating point math.It's not a given that the Arduino has enough memory for an expansive lookup table but there are similarly simple to use chips that do. The Teensy 4.0 comes to mind: It is 20 times faster in a benchmark, it runs at 600 MHz, has 1 MB RAM and 2 MB Flash (no problem with lookup tables!)https://www.pjrc.com/teensy-4-0/https://www.pjrc.com/store/teensy40.htmlIt can be programmed using the Arduino platform even though the devices have almost NOTHING in common.ETA: The Teensy 4 includes a 32 bit or 64 bit floating point unit for those times when you really have to do the math!Do op amp phase shifters play into this? If you can generate one 400 Hz waveform, it is possible to use RC networks and op amps to create phase shifted versions. Then the analog multiplier can deal with the amplitude:https://circuitdigest.com/electronic-circuits/rc-phase-shift-oscillator-circuit-using-op-amp

author: rstofer
author_rank: Super Contributor
timestamp: August 23, 2019, 06:08:57 pm
content: We need to be realistic in terms of the sine wave generation. Generating a clean 400 Hz waveform with an Arduino is a stretch.If we assume 1 table lookup per point and a 10 bit DAC we would need to generate 400*1024 (409,600) interrupts per second. There's almost no point in going to a 12 bit DAC as that would require 400 * 4096 (1.6 MILLION!) interrupts per second. I'm not sure the Arduino can even do the 410k interrupts but I am really sure it won't do 1.6 million.We clearly need to generate ALL of the outputs from the same interrupt, one way or another.So, how do we get the Arduino out of the waveform loop? We use something like the AD9833 to generate the reference waveformhttps://www.analog.com/media/en/technical-documentation/data-sheets/AD9833.pdfI didn't study the datasheet all that much but it appears you can enter a phase offset value. So, if it is necessary to generate signals with 120 degree phase shifts, use 3 of these signal generators and program the phase values. More study needed...Do everything necessary to get the slow AVR out of the signal generation loop. There's a reason that analog computing is still around!Step 1, experiment with AD9833s to see if it is easy to generate either 1 or 3 phase shifted signals. Don't worry about the details of amplitude, just get the proper signals. You can always amplitude modulate them later on.ETA: There is an Arduino library for the AD9833https://github.com/Billwilliams1952/AD9833-Library-Arduino

author: jmpowell
author_rank: Newbie
timestamp: August 23, 2019, 11:39:55 pm
content: Ideally, there is no electrical phase shift between any of the 400Hz signals. Small amounts (a few degrees) of phase shift are generally tolerable. Larger amounts introduce increasingly unacceptable errors.The waveforms do not have to be particularly pure. I have seen a surplus aircraft ADI operate from an unfiltered "modified" sinewave power inverter. I don't know what it did to the accuracy (probably nothing good), but there was no apparent problem.Cost may be a factor for some applications of a digital-to-synchro converter. Certainly it was for the ones I developed. The converters were to be used in hobbyist built flight simulators. Using real flight instruments and gauges boosts realism, but the more you use, the more converter$ you have to come up with. Several years ago using a brain dead MCU with external DACs was a sweet spot cost-wise. Today, a few dollars buys far more so it does seem interesting to explore other design approaches with current hardware.There are a few references for synchros that are worth the effort of browsing through. Here's a link to one:https://www.analog.com/en/education/education-library/synchro-resolver-conversion.html

author: rstofer
author_rank: Super Contributor
timestamp: August 25, 2019, 06:11:22 am
content: In terms of just getting a single 400 Hz sine wave, my experiments with the AD9833/Arduino were very successful:https://www.eevblog.com/forum/microcontrollers/why-arduino-users-so-agressive/msg2640903/#msg2640903

author: Yansi
author_rank: Super Contributor
timestamp: August 27, 2019, 08:21:38 am
content: Quote from: rstofer on August 23, 2019, 06:08:57 pmI can't figure out how did you come up with this. To produce a clean 400Hz from a DAC, from theory, you need just twice the frequency for sampling rate. For practical reasons, standard 8kHz audio sample rate would be more than fine to reproduce the signal.If you would not want to fiddle with steep filters to get aliasing out, you could just sample at the standard rate of 48kHz, which is more then enough for a 400Hz signals to be produced very cleanly.I am not sure what the OP needs (this whole thread is a mess), but if just three or four channels are required of some sort of signal, get any cheap ARM microcontroller with a couple of I2S interfaces, slap there twoCS4334 audio DACsand voila, problem solved.You can't do any simpler than that. Slap there for example aSTM32F072, couple of the above mentioned DACs, done. No crazy interrupt rates required (we have a DMA), no crazy sample tables. Sinewaves can be even calculated on the fly with just couple lines of code. (And no, I do NOT mean to calculate it using sinf(x), there are way easier solutions to that, such as an oscillating differential equation).QuoteThis is definitely not the reason.

author: richfiles
author_rank: Regular Contributor
timestamp: November 07, 2019, 03:12:24 am
content: Just commenting to say I'm still alive!The setup I had planned on building has a hardware based sine generator. It doesn't rely on the microcontroller or the DACs for sine generation, only sine attenuation and polarity flipping, through the use of multiplying DACs and an analog switch IC to select and inverted or a non inverted sine wave, generated by hardware. For me, it was easiest to use hardware I had on hand, and it cut sine generation out of the program altogether. These details do seem to get missed by a lot of people posting here. More than once, people have suggested I do exactly what I already plan to do!• Hardware generated sine wave.• Multiplying DACs• Microcontroller only controls polarity of the sine wave and the attenuation.Since there were still questions, I'll try first to explain synchros:The best way I can think of to describe a synchro, is if you take a single phase rotor, and mount it inside a three phase stator. That's literally it.ALL the outputs are synchronized to the single 400 Hz reference that is fed into the rotor. What changes, is the angle of the rotor, in relation to the three phase windings of the stator. When looking at a single winding, for every 90° of rotation, you get a peak, a zero, a peak in the opposing polarity, and another zero crossing... A sine wave. Think of how an amplitude modulated carrier wave works. The carrier stays at 400 Hz, in this case, but the amplitude changes. The positive portion of the sine angle of the rotor's position translates to an in phase output on the stator winding, and the negative portion of the sine angle of the rotor's position translates to an out of phase output on the stator winding. The phase alignment of the outputs always remain in sync with the reference input, but it's the attenuation between peak and zero, and the polarity of the phase that changes. Each stator winding is 120° apart, and so you have to look at the rotor's position, relative to the winding's angle.Interestingly enough, you could probably recreate a similar effect with some linear potentiometers attached to a crank. Connect the non-inverted reference to one side of the pot, the inverted reference to the other side of the pot, and take each of the three synchro outputs from the three pot's wipers. Attach all three pots sliders radially to a crank and rotate the crank. That might be the best visualization I can come up with. Synchros just do this with inductive windings, so they function like a transformer. Since they are transformers, they require AC to operate.Second, I'll try to break down my theoretical method (it's not tested, built, or anything) for clarity.• A hardware generator creates a 400Hz sine wave• The 400Hz sine wave is fed into a pair of Op Amps: One inverting and one non-inverting. This creates two sine waves 180° out of synch with each other.• The two sine waves are fed into an analog switch IC. The microcontroller can select the inverted or the non inverted signal to pass through.• The selected sine wave is fed into the reference of a 12-bit MCP4922 DAC.• The microcontroller sets the scaling of the DAC, allowing the DAC to function in multiplier mode, attenuating the sine wave on the reference.•For reference, there are a total of 9 analog switches, and 9 DACs, three per axis, for each of the three different axes. Each circuit is just repeated 9 times• The Microcontroller receives serial data containing the Yaw, Pitch, or Roll angle. (Each axis will be a separate PC board, and likely have it's own microcontroller).• The microcontroller will add 120 and 240 to the angle received, then check if any results are 360 or greater, and if so, subtract 360 from the result.• The three values are used to look up the attenuation value from a lookup table of sine values. (I think that might be easier than trying to calculate sine. Not sure)• Each of the three values returned are checked to see if negative. If negative, the associated analog switch has it's state set to select the inverted sine wave input.• The absolute values are sent to the three DACs of each axis. This allows the DAC to function as a multiplying DAC, scaling the analog sine wave on the reference.• The output of the three DACs are fed into audio amplifiers.• The three audio amplifiers are fed into transformers to couple into the synchro inputs of the FDAI.• The non-inverted reference is fed into a power amplifier, and is fed into a step up transformer to power the FDAI and provide it the reference source.As far as I can tell, that covers just about everything. Since programing is my weak point, I'm taking efforts to make sure as much as possible gets done at a hardware level, so the microcontroller side ends up as low effort as possible. Each axis microcontroller should only need a serial input to read incoming data, an SPI out to command two DAC chips, 2 Chip Selects for the two DACs (the chips are dual 12-bit DACs), an optional pin for synchronized updating, and three outputs to the analog switch ICs to select the polarity of the sine wave input. That's pretty straight forward. 5 (optionally 6) digital outs, 1 serial in (whatever interface works), and one SPI out.My reason for coupling with transformers was simply so I can both level shift and float the output so it's not tied to any reference. Also, since synchros are inductive devices, I was just trying to keep the coupling inductive. The DACs I'm using fit my budget, but it means I'm dealing with all 0-5 volt, single rail analog. I suppose capacitive coupling might be possible too, assuming the FDAI's controller pack is looking for just voltage differentials. If that's the case, I wonder if I even need the beefy audio amplifier chips on anything but the reference (since that has to actually power the entire unit)? I dunno. I figure, I can possibly "cheat" and use a US power supply transformer to drive the reference. I'd feed the output of the reference audio amp into the secondary, and hopefully, have enough current on the 115 volt primary side to actually power the unit. I can't say i know what the power requirements for a mid 1970s era mechanical ADI even is. I also don't know if feeding 400 Hz into a US 60 Hz transformer is okay to do. I know that at 400 Hz, transformers tend to be smaller, which is one major reason aviation uses so much 400 Hz AC equipment... Smaller transformer means lower mass. I don't know how much losses this will result in, or if I can even find an appropriate transformer to perform the step up. In general though, that's the one area I know I absolutely will need a transformer.

author: richfiles
author_rank: Regular Contributor
timestamp: December 12, 2021, 01:06:50 am
content: I started a new thread on the reference power amplifier.I had a positive development, thanks to a random person on the internet jumping in to lend a hand.https://www.eevblog.com/forum/projects/28vac-115vac-inverter-that-can-be-driven-by-400hz-analog-sine-wave/Provided everything checks out, that portion of the design appears to be complete!I'll need to order parts, and a PC board, and build the circuit.That just leaves the three-axis analog switch/DAC boards to build. I may follow up with the same guy on his recommendations for the 28vac output stages for this one. I had planned to use dedicated audio power drivers for the task, but if he recommends something far simpler, then there's no reason to tie a specific, specialty audio component to the design. All in all, progress is starting to pick up again, and the hardest portion of this build is now fully designed!