Issue with my VCO design  - Page 1
Forum section: electronics / beginners

author: CrackersX
author_rank: Contributor
timestamp: October 24, 2024, 09:17:18 am
content: Hey,I am a french student learning electronic (I have o amp theory, not transistors). I have been trying to create my own design of a VCO.First I wanted to create the signal.Here’s the ShematicI have trouble dealing with the multiplier (AD633JN) , I think that’s him that make the simulation crash like in the pic: ( we see that the signal is going to get good but it crash):doAnalyses: TRAN: Timestep too small; time = 0.00130097, timestep = 1.25e-17: trouble with node “h.xu1.hlim#branch”Without it the circuit works perfectlyIf you got any advice, solutions to get rid of the issue and to upgrade it: tell me !(I don’t want to copy a premade circuit but to do it my own way)Sorry for bad englishThank you for reading,Crackers.

author: CrackersX
author_rank: Contributor
timestamp: October 24, 2024, 10:33:12 am
content: .

author: Harry_22
author_rank: Frequent Contributor
timestamp: October 25, 2024, 03:04:06 am
content: Hi!Could you explain in more detail what your own VCO design is.PSIs the op amp U1 connected correctly?

author: Zero999
author_rank: Super Contributor
timestamp: October 25, 2024, 07:47:35 am
content: U1 is a Schmitt trigger and U2 an integrator.Have you built this, or is it just simulation?Have you tested the model at DC?

author: CrackersX
author_rank: Contributor
timestamp: October 25, 2024, 08:33:59 am
content: I changed the design so it works better.I'm no longer using the multiplier because I could just amplify the signal after with a amp invereter circuit and the result would be the same right?Explication:The goal is to make all the different signalsThe base of the circuit rests on the hysteresis comparator (bottom left) coupled with the integrator (bottom right) to have square and triangular signals. At the top there is a follower and then a low-pass filter to get the sinusoidal signal.(might be not the best way to do it but it was the only thing I thought)I'm missing the sawtooth one. I was thinking of starting from the triangle butI don't see how to get to the sawtooth signal?The variable resistance is used to change the frequency of each signal.(I will then in a second part amp the signal and filter it but later)I built in real life the first part ( hysteresis comparator (bottom left) coupled with the integrator (bottom right)) and it works as in the simulation nowTy for answers.

author: Zero999
author_rank: Super Contributor
timestamp: October 25, 2024, 09:34:51 am
content: Now it's just an ordinary oscillator, no longer voltage controlled.The problem with using a filter to get a sine wave, from a triangle, is the amplitude and wave shape, will alter, as the frequency of the oscillator changes.A sawtooth wave is made by charging a capacitor, via a constant current source and discharging it as quickly as possible.Why not store the waveforms in flash memory and use a DAC to generate he analogue signal? Then all you need to do to adjust the frequency is change the clock frequency?

author: CrackersX
author_rank: Contributor
timestamp: October 25, 2024, 10:11:47 am
content: Now it's just an ordinary oscillator, no longer voltage controlled. -> Um you are right. I'll get back to the multiplier (and the problems)I understand for sine wave. I will try to find another way to do itWhy not store the waveforms in flash memory and use a DAC to generate he analogue signal? Then all you need to do to adjust the frequency is change the clock frequency? -> I don't have digital electronic theory and it seems complicate, I might stick to an entire analogic approach.The thing I don't understand is how to change frequency with voltage. The multiplier was just changing the amplitude and I could just change the amplitude at the end of the circuit (in a VCA), so the multiplier wasn't useful?

author: CrackersX
author_rank: Contributor
timestamp: October 25, 2024, 10:16:18 am
content: Also,Isn't there a way to voltage control a variable resistor, so I don't need the multiplier anymore? Because I have the impression that multipliers are not components often used in the VCO environment and electronics in general

author: Zero999
author_rank: Super Contributor
timestamp: October 25, 2024, 10:54:16 am
content: Quote from: CrackersX on October 25, 2024, 10:11:47 amOn the contrary. It's much simpler to do it digitially. In the past, the problem was stortage space for the sinewave, but that's not been a problem for years.QuoteThe sine wave filter willl attenuate higher frequencies more, so the sine output voltage will drop, as the frequency is increased.Quote from: CrackersX on October 25, 2024, 10:16:18 amThere are a few ways to do that, but the simplist one is to use a digital poentiometer and an analogue to digital converter.https://www.analog.com/en/resources/design-notes/using-an-analog-voltage-to-control-a-digital-potentiometer.html

author: CrackersX
author_rank: Contributor
timestamp: October 25, 2024, 11:09:23 am
content: Thanks for the answer,On the contrary. It's much simpler to do it digitially. In the past, the problem was stortage space for the sinewave, but that's not been a problem for years. --> ye I understand but I have not studied this part of electronics and getting into it seems difficult for myself (if I knew both I would probably do what you say since it's logical that digital > analogic nowadays).The sine wave filter willl attenuate higher frequencies more, so the sine output voltage will drop, as the frequency is increased. -->forggeting sine wave, the thing I was saying was about Triangle waves (or square), what's the use of the multiplier apart of increasing the amplitude that I could increase later in the circuit?There are a few ways to do that, but the simplist one is to use a digital poentiometer and an analogue to digital converter. -> do you have a guide, circuit or something to start looking for it? Is it a viable solution for the VCO like worth for me to learn that tool?

author: CrackersX
author_rank: Contributor
timestamp: October 25, 2024, 12:03:05 pm
content: mb I didn't see the link you provided, I will try simulating those components, it seems to be goood thanks

author: CrackersX
author_rank: Contributor
timestamp: October 25, 2024, 12:49:22 pm
content: I cannot find spice models, is it even possible to simulate those components in NgSpice ?

author: Zero999
author_rank: Super Contributor
timestamp: October 25, 2024, 01:30:50 pm
content: Quote from: CrackersX on October 25, 2024, 12:49:22 pmNo, there isn't a simple way to simulate a microcontroller, using Ngspice. There are simulators which can do that, Proteus springs to mind, but why would you want to, for such a simple project like this?Again, why do you want to simulate a digital potentiometer? Just use an ordinary potentiometer. If the software you're using lacks one, it can be modeled as two resisors in series. Here's a tutorial on how to simulate a potentiometer. It's for LTSpice, but could be adapted for other simulators.https://www.eevblog.com/forum/beginners/simulating-potentiometers-using-ltspice/You do realise just because it works in a simulator. It dosn't mean the circuit is any good or will work in real life.

author: WillGordon1
author_rank: Newbie
timestamp: October 25, 2024, 02:04:15 pm
content: Please - please - please. I am 1 hour old at this forum. This is the first place I found that I can post.I would like to know where and how I can ask a question on the use of the 74HC4046 (PLL). Please provide me the steps required to do this. Remember, I know nothing about EEVblog. I'm not even sure where anyone's answer will appear. My email is abroresources.comThank you

author: Zero999
author_rank: Super Contributor
timestamp: October 25, 2024, 02:46:01 pm
content: Quote from: WillGordon1 on October 25, 2024, 02:04:15 pmWelcome to the forum. Just a few points:1) Please create your own thread, rather than hijacking someone else's.2) It's a bad idea to make your email public like that, as it encourages spam.3) What do you want t accomplish with the 74HC4046?

author: Zero999
author_rank: Super Contributor
timestamp: October 26, 2024, 07:41:27 pm
content: Quote from: CrackersX on October 24, 2024, 10:33:12 amWhy did you remove that post?It contained an AD633 model. Which one was it?I downloaded one from AD and simulated it.https://www.analog.com/en/products/ad633.html#tools-headerI tied X2 and Y2 to 0V. V3 was swept from -10V to 10V and the output plotted, with V4 set to -10V, -6V, -2V, 2V, 6V and 10V. The X axis is V3 and the Y axis, the output voltage. A different colour is used for each voltage of V4.It looks pretty good to me.

author: CrackersX
author_rank: Contributor
timestamp: October 27, 2024, 10:54:55 am
content: Hey,Quick update on my research on that project,I realised that the first design was not great for a VCO since the result was "pic 1".I will go back to the design "pic 2", I have to find a way to make sawtooth as well as sin wave out of triangle or square (which I could I have created apart of the circuit like in "pic 3" but I feel like creating those 2 last waves out of triangle or square might be better (and funnier :>), I think it is possible with diodes but idk howWhen I have all the waves I will consider buying digital potentiometer to test that IRL :>.I would like to create a VCO with additive synthesis in parallel, it could be simpler to create for my use.It would be necessary to create a sin oscillator then duplicate the signal and amplify all signals differently then sum all the signals of different amplitude (already with 5 signals I think I can have a good result). I do not see any design like that, why?Ty for your time.

author: Harry_22
author_rank: Frequent Contributor
timestamp: October 27, 2024, 11:08:09 am
content: Quote from: Zero999 on October 25, 2024, 07:47:35 amBrevity is the soul of wit!Now everything is clear how it works. I've never dealt with AD633 before. It turns out this is a signal multiplier. Pure mathematics. Cool!@CrackersXhave you given up on the project when all you have to do is take a small step to make it work? I’ll say something seditious, but the simulator is much more instructive for a radio engineer than a soldering iron. And it also requires debugging. I suggest you replace AD633 with a function source W=X1*Y1/10So it’s much easier to understand this black box even for simulator.Change V1 with 5v battery.PSSorry I have only Microcap. Otherwise l could help you.

author: Zero999
author_rank: Super Contributor
timestamp: October 27, 2024, 12:17:29 pm
content: Why not use the two op-amp + transistor VCO circuit to generate a triangle wave?VCO TL072.asc(5.41 kB - downloaded 47 times.)Then use a sine wave shaper circuit to get the sine wave. You could use the TL074, do only one IC is required,

author: CrackersX
author_rank: Contributor
timestamp: October 27, 2024, 06:17:09 pm
content: Can you explain the VCO circuit please ?

author: Zero999
author_rank: Super Contributor
timestamp: October 27, 2024, 07:33:53 pm
content: U1 is an integrator. The rate of change of voltage on the output, depends on the input voltage. When Q1 is turned on, it's non-inverting, so the output voltage rises. When Q2 is off, it's non-inverting, so the output voltage falls.https://en.wikipedia.org/wiki/Integrator?useskin=vector#Op_amp_integratorU2 is an inverting Schmitt trigger.https://en.wikipedia.org/wiki/Schmitt_trigger?useskin=vector#Inverting_Schmitt_triggerWhen the voltage on the integrator's output exceeds the off threshold voltage of the, the Schmitt trigger, the output of the Schmitt trigger goes low, switching the integrator to inverting mode, causing its output voltage to fall, until it falls below the on threshold of the Schmitt trigger, which causes its output to go high and the integrator to go into non-inverting mode.Here's a website which explains it better than I do, but my circuit is subtly different. The values of the R1 and R2 are much lower, so the input to the op-amp is near the control voltage. My circuit also uses a BJT, rather than a MOSFET. The capacitor across R8 makes it turn off faster, by applying a negative pulse to the base.https://electronicscoach.com/voltage-controlled-oscillator.htmlSimulating the circuit and plotting the triangle and square wave outputs against one another makes it easier to understand.

author: BillyO
author_rank: Super Contributor
timestamp: October 27, 2024, 07:44:28 pm
content: I was going to suggest something very similar. The last one I built I used an LM358.

author: Harry_22
author_rank: Frequent Contributor
timestamp: October 28, 2024, 09:51:47 pm
content: Just finished VCO model in Microcap.I had to tinker a little with the time settings. Too many resources are spent on frequency measurement.Your original scheme works well.Congratulations!

author: CrackersX
author_rank: Contributor
timestamp: October 29, 2024, 01:09:54 pm
content: thank you,But the circuit isn't frequency controlled, so I'm going for the design just above

author: CrackersX
author_rank: Contributor
timestamp: October 29, 2024, 01:19:00 pm
content: I want to create sawtooth waves by modifying a triangle wave so that it's inverted only on the falling edge, essentially flipping it by multiplying by 1 and -1. My explanation might not be very clear, but take a look at the circuit for context.I also need to convert a square wave to a signal between -1V and 1V with a 0V DC offset. To address the DC offset, I'm using a 10 µF capacitor, but it's behaving strangely. Do you know why this might be happening?Thanks for the circuit design, by the way—it’s incredibly compact and beautiful. I’m just not quite there imagining that yet!Don't take in consideration the sin wave shaper, I will deal with it after the sawtooth waves working

author: Harry_22
author_rank: Frequent Contributor
timestamp: October 29, 2024, 03:52:15 pm
content: Quote from: CrackersX on October 29, 2024, 01:09:54 pmSorry, I didn't quite understand.

author: CrackersX
author_rank: Contributor
timestamp: October 29, 2024, 05:20:42 pm
content: Like changing the GBF value doesn't change the frequency of the output signal (sortie1 or sortie2) but the amplitude,isn't it? (you put me in doubt now)

author: Harry_22
author_rank: Frequent Contributor
timestamp: October 29, 2024, 09:00:38 pm
content: Do you doubt something, that you drew the diagram yourself and it works?In the previous picture with the red vertical “sticks” you saw that as the voltage increases, the frequency (height of the “sticks”) increases linearly. It was static measurement.Now a dynamically changing signal GBF has been given and we see how the accordion “plays”.This was your design of the circuit. There is no need to doubt that it really works.PSYou will find both simulations in the "Capture d'ecran" folder inside zip.Just unpack zip file to MC12 folder and run MC12 freeware application.https://drive.google.com/file/d/1MvPEWrPnJActRC2H1dEmYp3nr6EGssbp/view?usp=sharing

author: CrackersX
author_rank: Contributor
timestamp: October 30, 2024, 04:57:14 pm
content: Thanks, Do you know why people are not doing that VCO design usually, like I haven't see it in all of my research

author: Zero999
author_rank: Super Contributor
timestamp: October 30, 2024, 05:17:09 pm
content: Quote from: CrackersX on October 29, 2024, 01:19:00 pmThat schematic was riddled with errors.You forgot to add a zip file of your AD633J symbol, but there was no need to create one. Use DIP8 in the .The polarity to the AD633 was reversed.If you need a bipolar square wave, then add a negative supply to the VCO circuit.Here's your schematic with the errors fixed. It still won't simulate. It generates a time step too small error. Perhaps someone else can get it to work.Why not use a programmable inverter to flip the triangle wave? There's no need for the expensive AD633 just to multiply by either +1 or -1.

author: CrackersX
author_rank: Contributor
timestamp: October 31, 2024, 02:59:25 pm
content: do you have a circuit in mind for the programmable inverter?

author: Zero999
author_rank: Super Contributor
timestamp: October 31, 2024, 07:42:10 pm
content: It's a similar circuit to U1, except without the capacitor and referenced to 0V, rather than -V, so a JFET has to be used to deal with the negative current flow. Now there are three op-amps you can use the TL084 or TL074, but the model I have is for the TL072.The frequency of the sawtooth is obviously doubled.

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 01, 2024, 12:15:56 pm
content: I launched the circuit with two TL072.The steepness of the current characteristic (green dotted line) is significantly less than it was with AD633 (red dotted line).

author: CrackersX
author_rank: Contributor
timestamp: November 03, 2024, 09:23:57 am
content: this means that the model with the AD633 runs on a much lower (and steeper) bandwidth?So I better go on the transistor model

author: CrackersX
author_rank: Contributor
timestamp: November 03, 2024, 09:27:23 am
content: Well played, I thought of that but I hadn't been able to make it because I still have trouble with transistorsNext I have to divide by 2 the frequency of the sawtooth and add an exponential converter to the input (seems pretty easy since they are conponents thata are doing this exatcly) and I'm done ;>

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 03, 2024, 10:12:12 pm
content: Quote from: CrackersX on November 03, 2024, 09:23:57 amThe slope of AD633 characteristic curve is 10 times steeper.

author: CrackersX
author_rank: Contributor
timestamp: November 05, 2024, 04:58:14 pm
content: But why is it a problem for a synthesizer VCO design that S is high?I understand that controlled voltage will be harder to use since getting a specific frequency is more difficult, but can't I just adjust the frequency-to-voltage scaling in the circuit I already need to design for having S=1V/octave?

author: CrackersX
author_rank: Contributor
timestamp: November 06, 2024, 03:59:44 pm
content: I also tried building the first part of the circuit in real life (spoiler: it doesn’t work). I need to add test points, but I’m not sure where.Is there a way to set up the circuit on a breadboard on computer, so it’s easier and faster to build , read and troubleshoot from the outside?

author: BillyO
author_rank: Super Contributor
timestamp: November 06, 2024, 04:04:40 pm
content: This one works.[sponsored videos]

author: Zero999
author_rank: Super Contributor
timestamp: November 06, 2024, 05:37:42 pm
content: Quote from: BillyO on November 06, 2024, 04:04:40 pmThe circuit I posted will also work. I've built it before and know it works. It's not the schematic which is the problem because the one he posted should also work. The omission of the output zener diode will mean the output is no longer regulated and the lack of a 47pF capacitor, will prevent it from working at higher frequencies, but not at the low frequency it''ll oscillate at, with the given component values.Quote from: CrackersX on November 05, 2024, 04:58:14 pmSorry, I don't know what you're talking about.Quote from: CrackersX on November 06, 2024, 03:59:44 pmIn what respect does it not work?The problem with breadboard is it's prone to loose connections.Go through and check the connections against the schematic. Common errors are confusing 0V with -V and getting the pinout for the BJT wrong.Failing the above, try building another circuit with the op-amps, such as an amplifier with a gain of 2, to test they work. Test the transistor, either using another circuit or a tester device.

author: BillyO
author_rank: Super Contributor
timestamp: November 06, 2024, 05:42:32 pm
content: Quote from: Zero999 on November 06, 2024, 05:37:42 pmI agree. They are very similar circuits. I just posted the video to show these designs do indeed work.

author: CrackersX
author_rank: Contributor
timestamp: November 06, 2024, 08:12:37 pm
content: In what respect does it not work? -> I'm not seeing a triangle or square wave in my oscilloscopetry building another circuit with the op-amps, such as an amplifier with a gain of 2, to test they work. Test the transistor, either using another circuit or a tester device. -> I have tester for op amp and transistor, I tested the op-amps and transistors and verified the values for all transistors and capacitors. The issue seems to come from the connections I made, but it’s hard to spot the error once everything is assembled. It would be ideal to test it step-by-step, but the circuit only works when it’s fully assembled.I'll rebuild it with a clearer layout. Do you have the layout for the working circuit you built?P.S. Did you make a PCB layout? And don’t you mind sharing it so it saves me time, and I can upgrade it with the sawtooth part

author: Zero999
author_rank: Super Contributor
timestamp: November 06, 2024, 10:35:59 pm
content: The simulation shows the circuit will oscillate around 500Hz, when the input voltage is near the positive supply.I don't have time at the moment to post the simulations of higher frequencies, when the lack of the 47pF capacitor causes problems, but will tomorrow.

author: Zero999
author_rank: Super Contributor
timestamp: November 07, 2024, 05:21:00 pm
content: I changed C1 to 47pF, for a much higher output frequency.Here's the output waveform with C2 present. The output frequency is just under 47pF and the triangle wave looks good.Now, look at the waveform without C2. The output frequency has gone down and the amplitude increased to the point where the op-amp's output saturates close to either supply rail.

author: CrackersX
author_rank: Contributor
timestamp: November 09, 2024, 09:23:20 am
content: Okay, I’ll consider using it.I want to design the last part, which involves dividing the frequency of a sawtooth signal by 2. I was thinking about using the NE555, but I read that frequency division only works for square waves. I’m not sure how to handle that.

author: BillyO
author_rank: Super Contributor
timestamp: November 09, 2024, 02:46:36 pm
content: Quote from: CrackersX on November 09, 2024, 09:23:20 amI have to admit I am having real trouble trying to understand why you would want to do this. Can you let us know what the end goal to all this is?Also, do you mean "triangle signal" and not "sawtooth signal"?

author: CrackersX
author_rank: Contributor
timestamp: November 09, 2024, 04:16:17 pm
content: I want the sawtooth wave at the output to match the frequency of the square wave and triangle wave. Currently, it's at double the frequency, so I was considering using the NE555 timer to adjust it.

author: CrackersX
author_rank: Contributor
timestamp: November 09, 2024, 04:19:16 pm
content: So when I switch between square, triangle, or sawtooth, the frequency stays the same.

author: BillyO
author_rank: Super Contributor
timestamp: November 09, 2024, 04:27:44 pm
content: Quote from: CrackersX on November 09, 2024, 04:19:16 pmUse a type D flip-flop.https://www.falstad.com/circuit/e-divideby2.html

author: CrackersX
author_rank: Contributor
timestamp: November 09, 2024, 04:39:02 pm
content: The issue is that it outputs a square wave instead of a sawtooth wave divided by 2.

author: BillyO
author_rank: Super Contributor
timestamp: November 09, 2024, 05:59:49 pm
content: Correct, you will follow that with an integrator to feed your sawtooth making circuit.

author: CrackersX
author_rank: Contributor
timestamp: November 10, 2024, 11:08:09 am
content: but I will get a triangle wave /\/\I want a sawtooth /|/|

author: Zero999
author_rank: Super Contributor
timestamp: November 10, 2024, 11:22:15 am
content: Quote from: CrackersX on November 09, 2024, 04:19:16 pmWhy not simply use another set of contacts to switch in another capacitor in parallel with C1, when sawtooth wave is selected?

author: BillyO
author_rank: Super Contributor
timestamp: November 10, 2024, 11:46:01 am
content: Quote from: CrackersX on November 10, 2024, 11:08:09 amYou didn't read my edit? Go back and read my last comment again.

author: CrackersX
author_rank: Contributor
timestamp: November 10, 2024, 04:15:39 pm
content: Thanks! It turned out to be easier than I thought.I’m close to finishing the project and will consider doing the 1V/oct conversion later, as I’m not entirely sure how it works just yet.I'm controlling manually the switch to get right frequency on sawtooth (maybe I will try to line up it with triple switch)triple switch in the shematic = just to select 1 output with a switchI added an active low-pass filter (not voltage-controlled), and I’ll include a potentiometer to control the cutoff frequency and gain (see 'potentiomètre' in the notes). If I haven’t made any other mistakes, I should just need to connect the output to a speaker. I have this one (see pic 2) – can I connect it directly to the ‘signal filtre’ output, and will it work?

author: BillyO
author_rank: Super Contributor
timestamp: November 10, 2024, 04:26:57 pm
content: Those op-amps can technically handle a short on the output indefinitely, but doing so may cause it to dissipate too much power. I would use a 100Ω resistor in series with it to prevent the op-amp from over heating.

author: Zero999
author_rank: Super Contributor
timestamp: November 10, 2024, 10:38:28 pm
content: Quote from: CrackersX on November 10, 2024, 04:15:39 pmIt might make a sound, but it won't work very well because a TL072 can't output enough current to drive an 8 Ohm speaker properly. It will current-limit, resulting in distortion and low volume.A power amplifier is required to drive a speaker. A peak current of about 350mA is required to drive an 8 Ohm speaker at 0.5W RMS.

author: CrackersX
author_rank: Contributor
timestamp: November 12, 2024, 06:47:01 pm
content: Perfect! I will get one, I was just wondering:1)Will this simple filter design work effectively?2)Is controlling the filter with R19 or R14 the best approach (using the cutoff formulaCode:f_c = \frac{1}{2 \pi \sqrt{R_{14} \cdot R_{21} \cdot C_5 \cdot C_6}}, or is there another simple method? (Voltage control might be too complex for me at this point and isn’t necessary for the musical application I have in mind for this VCO and filter design.)Same for the gain

author: Zero999
author_rank: Super Contributor
timestamp: November 13, 2024, 12:44:12 pm
content: Why do you want to add a filter?This whole thread is one big xy problem.You've not states what your requirements are, so it's impossible to say whether your design is any good or not.

author: CrackersX
author_rank: Contributor
timestamp: November 16, 2024, 01:06:32 pm
content: I want to create a small synthesizer that's musically useful.The main objective is to recreate synth parts similar to the one linked. Listen at 36 seconds to hear the sound clearly. It’s just a simple sawtooth wave with a filter that opens linearly.Manually controlling the cutoff frequency should give me good results, but I’m not sure if it will work exactly as I want.

author: CrackersX
author_rank: Contributor
timestamp: November 20, 2024, 08:49:20 pm
content: I started debugging the circuit. I began with the hysteresis comparator, using an external function generator with a 20V peak-to-peak triangle wave. The comparator works well, but I noticed something strange when I checked the output of the transistor (see picture). Additionally, when I measured the input of the op-amp, I observed a constant signal with minimal oscillation. This seems to be because the square wave from the transistor has an amplitude that is too low.I believe I didn’t make any mistakes while assembling the circuit (I rebuilt it more clearly; you can verify it : V3 is +15V and V4 -15V ,yellow cable on the right is just the one from the oscilloscope).Ty for your help

author: Zero999
author_rank: Super Contributor
timestamp: November 23, 2024, 10:45:17 pm
content: Testing the Schmitt trigger separately is a good idea.What exactly is strange about the output of the transistor?Please upload screenshot of the oscilloscope, preferably by saving an image of the screen, rather than taking a photograph and state exactly where the probes are connected.

author: CrackersX
author_rank: Contributor
timestamp: November 27, 2024, 03:19:16 pm
content: Hi everyone,Apologies in advance—I can only upload images for now. Here’s the situation:Image 1This shows the integrator alone. I tested it using a square wave from a function generator as input. Apart from some saturation (likely because I didn’t set the correct amplitude for the square wave), it seems to work as expected.Image 2This is the hysteresis comparator by itself. The input is a 20 Vpp triangular wave (to trigger the comparator thresholds), and the output—measured at the output of the second op-amp—looks great!Images 3 & 4These show what I observed when measuring the signal just after the transistor using my oscilloscope. The green signal has a very small amplitude (and seems saturated). Is this normal?From my understanding, I should see a square wave at this point. Or is measuring the voltage here not particularly useful because the transistor's role is more about controlling the current flow? Specifically, the transistor should alternate between:Allowing current to flow linearly to the capacitor (enabling the integrator to work in one direction).Blocking current, allowing the capacitor to discharge through R1 (making the integrator work in the opposite direction).That leads me to a couple of questions:Is the small signal amplitude after the transistor expected?Why do we need to divide the voltage going into the first op-amp?Is my understanding of that transistor right?I’m trying to make sense of the transistor's role and how the circuit dynamics are working. Any clarification or advice would be greatly appreciated!Thanks so much for taking the time to read and help—it really means a lot to me.

author: CrackersX
author_rank: Contributor
timestamp: November 27, 2024, 03:21:01 pm
content: the last 2 imagesFor context: the red wire is from the function generator (GBF), and the violet wire is from the oscilloscope.

author: Zero999
author_rank: Super Contributor
timestamp: December 02, 2024, 10:48:59 pm
content: Have you tried building the integrator part?Appling a square wave to Q1 results in an output square wave, with a rise/fall time i.e. slew rate dependant on the control voltage. I've added Q2 so it can be driven with a signal generator set to 5V and referenced to 0V. If it's practical to reference the signal generator to -V, then you can omit Q2 and drive Q1 via a 10k resistor.

author: CrackersX
author_rank: Contributor
timestamp: December 18, 2024, 04:30:51 pm
content: Hi,I’ll try to work on that circuit later. It’s been a month now that I’ve been struggling with it. To lift my spirits, I went back to my first design (with the multiplier). I built it, and I’m getting perfect results.I don’t understand why no one uses this design—just look at the graph! I’m achieving a perfectly linear evolution.Can you help me understand why this model isn’t commonly used?

author: Zero999
author_rank: Super Contributor
timestamp: December 18, 2024, 07:30:31 pm
content: Good. I'm glad you've got the multiplier design to to work.As to why no one uses it: cost is probably the main one. The AD633 is not cheap, compared to the LM393 which is a fraction of the price.https://www.tme.eu/gb/details/ad633jrz/analog-multiplexers-and-switches/analog-devices/https://www.tme.eu/gb/details/lm393d-st/smd-comparators/stmicroelectronics/lm393d/I had another idea: replace the LM393 with a 555 timer. It simplifies the circuit, as it gets rid of a few resistors. You might have better results with a CMOS version such as the 7555, TLC555, TS555 etc. The main downside is the maximum total power supply voltage can't be over 18V (+/-9V).

author: CrackersX
author_rank: Contributor
timestamp: February 26, 2025, 06:15:20 pm
content: I’ll stick to the design we worked out earlier and go straight to building the PCB because I’ve had enough of dealing with breadboards that never seem to work.I’ve made good progress on the overall synthesizer, so I might close this topic and open a new one dedicated to the entire project.Feel free to help it there:https://www.eevblog.com/forum/beginners/reviews-on-the-shematic-before-building-and-ordering-the-pcb-of-my-synthetiser/