Real World Use Of A Function Generator   - Page 1
Forum section: electronics / beginners

author: The_Welding_Library_Guy
author_rank: Contributor
timestamp: February 05, 2019, 07:45:43 pm
content: Hi All,Im in the process of building up a electronics work bench and have spend a bit of time on google looking at all kinds of enticing toys. I have been thinking about looking for a scope and function generator but I had a question. I know a scope is must have gear and I know you use a function generator to generate signals veiwable on your scope. But other then helping you learn how to use your scope with a controlled signal. Is there any other real world use for one?Thanks

author: rstofer
author_rank: Super Contributor
timestamp: February 05, 2019, 08:01:55 pm
content: Of course there is! In fact, just plugging the output of a signal generator into a scope is pretty meaningless unless your generator is building up some non-sinusoidal waveform.https://www.eevblog.com/forum/chat/a-valentine_s-day-activity-for-your-scope-and-function-generator/msg1136847/#msg1136847You may decide you care about amplifiers or filters. In this case, you want to generate very clean sine waves that you can use to check for things like gain and phase versus frequency. Yes, a network analyzer is more useful than a scope in this regard (usually) but we use what we have.You might be building some kind of digital frambus that needs a clock input.I'll concede that the signal generator is my least used piece of equipment but I don't do a lot of analog work. Other than analog computing, my interests lie in the digital domain or FPGAs and uCs.Give serious consideration to the Digilent Analog Discovery 2. You get a 2 channel signal generator, a two channel scope, a dual output power supply, 16 bits of digital IO including the ability to function as a logic analyzer and decode various protocols and so on. Most people ignore it but they really shouldn't. It is a complete lab in a small box.Oh, and the Waveforms software does a much better job of making Bode' Plots than you will ever get with a signal generator and scope. You can download the software and tinker with it in 'demo' mode.

author: Wimberleytech
author_rank: Super Contributor
timestamp: February 05, 2019, 08:03:32 pm
content: Quote from: The_Welding_Library_Guy on February 05, 2019, 07:45:43 pm1) Use them as a clock source for a digital circuit you are building/breadboarding2) Use an input signal to sweep over a range of frequencies to characterize the frequency response of a circuitI seldom need one. Sold the ones I had. I do have a little Chinese function generator (off ebay) for the rare time I need one.

author: bsudbrink
author_rank: Frequent Contributor
timestamp: February 05, 2019, 08:18:03 pm
content: Quote from: The_Welding_Library_Guy on February 05, 2019, 07:45:43 pmAbsolutely. You use it to put complicated looking Lissajous patterns on your scope to impress visitors/your spouse.

author: GreyWoolfe
author_rank: Unknown
timestamp: February 05, 2019, 08:38:50 pm
content: Quote from: bsudbrink on February 05, 2019, 08:18:03 pmAnd granddaughter.

author: jpb
author_rank: Super Contributor
timestamp: February 05, 2019, 09:03:28 pm
content: Should be a lower priority than a scope, but very useful to have if you want to either produce clock signals or analogue signals for injection into circuits being tested or repaired.I tend to use mine for fairly random things. The last time I used it was just to check some minicircuit mixers I'd bought of ebay. The last real use was when I was mending a radio frequency standard and I wanted to inject 198kHz in at a very low level rather than wonder if the antenna was picking up the signal. It made it very easy to tune the varicaps and so on.But it is as others have said, it really depends on what sort of electronics you're into. If you're into RF then a function generator can be used for modulation of an RF signal genrator. If you're into digital you might want to experiment with different clock rates. If you're building things with sensors it might be useful to emulate the sensor whilst working on the rest of the circuit. If you have one with arbitrary wave form capabilities you can emulate heart signals if you're designing a monitor. If you're into wild life you might want to generate ultrasonic signals to interact with bats!

author: bsudbrink
author_rank: Frequent Contributor
timestamp: February 05, 2019, 09:11:51 pm
content: Bats! Definitely bats!

author: H713
author_rank: Regular Contributor
timestamp: February 06, 2019, 05:37:30 am
content: Mine sees as much use as my oscilloscope. You're working on amplifiers, you need something to feed a test signal. You want to know how much power the amplifier you designed is making, what its open loop vs. closed loop gain is, you need something to drive a clean sine wave into it.That said, if you are into audio, there are other options that are better than a standard function generator.As an example, the output from an Audio Precision will be MUCH lower distortion than any signal generator, so once you get one of them you won't use your function generator nearly as much. That said, the AP box is a serious investment. You can also use a computer sound card to do it (at least at audio frequencies). A Soundweb London can also be configured as a very good sine/square wave generator.If you are doing audio, however, you really want something with balanced XLR outputs. Might be able to build up something, but if I'm honest, when I redo my bench the Wavetek will likely see very little use.Most of what I just said is specific to audio- but in general, I think it's worth having.

author: cdev
author_rank: Super Contributor
timestamp: February 06, 2019, 06:18:36 am
content: Quote from: The_Welding_Library_Guy on February 05, 2019, 07:45:43 pm

author: Shock
author_rank: Super Contributor
timestamp: February 06, 2019, 01:58:44 pm
content: Mostly used to evaluate the performance or operation of a circuit or to replicate or replace an input to another circuit.If you buy a Chinese AY-AT Component tester, which is about the cheapest option with other handy features, they may have a simple function generator built in (check first). Or if you are getting in audio you can pick up an audio generator (especially cheap ones without a display) for $20 or so upwards.The other thing you can try is make up a DIY signal generator, logic pulser, signal injector etc for a bit of construction and oscilloscope experience. Good project in tandem with a simple audio amplifier as well.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 06, 2019, 02:12:45 pm
content: Not very long ago I decided to finally buy a Function generator.I bought the cheapest version of the JDS6600 with a 15MHz bandwidth.It is one of the tools I should have bought much earlier.When I was young (30 years ago) a function generator with such specifications was ... expensive, almost non-existant, and then you sort of fall in a pattern of building simple test signal generators for separate projects.My last serious use of my JDS6600 was for an Inductor tester. I built a circuit on Veroboard with a Fet driver, a beefy N-channel MOSfet, a bank of Elco's and an inductor to test.For test signals I needed narrow pulses to measure the current through the inductor and other things. There are many variants of power inductor testers:https://duckduckgo.com/html?q=power+inductor+testerI simply copied the schematic from the first link:https://ludens.cl/Electron/lmeter/lmeter.htmlSuch an inductor tester is a pretty trivial circuit. Most of the components and connections are in the 2 NE555 IC's, which are used as a simple signal generator (Frequency and pulsewidht). Instead of those NE555's I just hooked up my Function generator which saves me some time and also has much more accurate control on the test signal that goes into the MOSfet.There are many of such test circuits which can be simplified by using your function generator instead of soldering together a custom signal generator.Another recent quick use of my Function generator is for testing stepper motor drivers. You can easily generate step pulses to test what the maximum motor RPM is with different power supply voltages and loads.And that's only a small part of the PWM signal generator part of this thing.In the analog domain it can also do much more than I have used yet.With the 2 syncronised outputs of the JDS6600, Lissajous figures become so trivially easy it's boring, but if you want you can add some drift by changing one of the sine's in steps of 0.01Hz.One of the classic first transistor circuits when you start with electronics is a single transistor amplifier with a few resistors. To test this, you need an input signal and a function generator is an easy source for test signals.What you get for around EUR 60 is amazing, but in this price range it's got some limits.The power supply adapter is garbage. Throw it away and use a decent adapter, or put a simple block transformer + LM7805 in the thing itself. Plenty of room.On low amplitude it gets a bit noisy. The signal is generated by a 12-bit ladder DAC on the output of an FPGA.If your're into audio you can use some (decent) extra USB audio adapter and modify it a bit to get a pretty decent / low noise audio source. There are loads of programs available to generate live audio signals (Sine, triangular, sweep, whatever). You can add some switches and pot meters for easily accesable adjustments for volume AC/DC coupling and offset. But I'd rather have my JDS6600 for almost any signal (When the low-noise is not a big point).

author: LapTop006
author_rank: Unknown
timestamp: February 07, 2019, 10:20:51 am
content: As others have said, it's not one of the pieces of kit you buy first off.A year ago I had none, now I have three, two quite specialised & handy in their niches, but otherwise not very useful, and a general function gen (in my case all three are from Stanford Research).If you're purely doing microcontroller work they might not get much use as anything other than an occasional clock, but if you're doing analog or RF they're really handy.

author: Rerouter
author_rank: Super Contributor
timestamp: February 07, 2019, 11:01:29 am
content: I should point out most "Function Generators" these days are actually Arbitrary Waveform Generators, Now what difference does that make? well it lets you abuse it in fun ways.For digital, your trying to reverse engineer a bus, so do you spend a day building something to playback a protocol message at an exact moment, or load the pattern into a AWG and use its trigger input, and have it respond in nanoseconds, Equally, how does the device behave if I slow things down or speed it up, what if I slice out the dead time, so its 100% protocol load, what amplitudes are valid, and the best one, what unspeakable bugs appear after 24 hours of noise in the correct frequency and amplitude range, I've used mine for playback attacks on some fun things, (send a small set of messages back and poke at what changes each time)Equally with multiple outputs, its easy to quickly roll your own PSK / ASK / FSK etc encoding, some can even use the trigger to switch this internally, so again, instead of needing to program up for it, just feeding a TTL converter to its input trigger gives you a way to generate a silly amount of protocols.

author: Wimberleytech
author_rank: Super Contributor
timestamp: February 07, 2019, 01:21:55 pm
content: QuoteYou have damn near convinced me that I should have one on my bench!!

author: bd139
author_rank: Super Contributor
timestamp: February 07, 2019, 07:16:34 pm
content: I use my function generator all the time. 90% of what I do is playing with signal processing of some sort in the audio and RF frequency domains.Without a wide range signal source it's a total pain in the arse doing a whole class of testing. Even fixing basic things tends to require a signal source.Currently have an HP 33120A AWG but have had a couple of analogue ones and a Rigol one before that.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: February 08, 2019, 03:18:04 am
content: Quote from: bsudbrink on February 05, 2019, 08:18:03 pmI don't have one. Just a pulse generator which gets seldom use. Every project I have done has relied on itself to generate all necessary signals starting from the wall socket and downstream from there. Wait a minute - I just made an audio oscillator of high purity to test possible audio projects, so there's that.

author: JonPyro
author_rank: Regular Contributor
timestamp: February 08, 2019, 07:01:36 pm
content: I am always finding uses for my generator. Just today I wanted to quickly do some motor control work and used it to generate a PWM. Saved a lot of time having to get a micro out and program it etc.

author: bob91343
author_rank: Super Contributor
timestamp: April 26, 2019, 04:48:27 pm
content: Perhaps a more interesting question might be 'real world use of two function generators'.I was bemoaning the fact that I have three function generators but wish I had an arbitrary waveform generator. But perhaps I can combine two of my function generators to create one.I recall back in the early 1960s I worked for a company that made a function generator. It was housed in perhaps two or three six foot racks, all tubes of course, with many 10 turn potentionmeters to set various points on the desired waveform.I never used or worked on this device but found it fascinating.I do believe that with use of some of the rear panel auxiliary inputs I can make a staircase wave or something like it. Any ideas? I haven't given this much thought yet so maybe I can answer my own question.

author: Wimberleytech
author_rank: Super Contributor
timestamp: April 26, 2019, 05:13:17 pm
content: Quote from: Wimberleytech on February 07, 2019, 01:21:55 pm...and I did! A Siglent

author: soldar
author_rank: Super Contributor
timestamp: April 26, 2019, 06:48:00 pm
content: Quote from: bob91343 on April 26, 2019, 04:48:27 pmLookup table and counter?

author: rstofer
author_rank: Super Contributor
timestamp: April 26, 2019, 07:33:43 pm
content: Function generators are of some use in education. You really don't 'get' AC impedance until you play with it on the bench. A signal generator, a resistor and capacitor along with a DMM and perhaps a scope really add to the learning. Use the DMM for attenuation and the scope for phase shift.I remember this exercise from a Circuits Lab I took back in college ('74?) and I still demonstrate it to my grandson and will again when he gets to his Circuits course in a year or so.Or, maybe you are playing with RC servos and you want a precise pulse width at a 50 Hz rate. That's pretty easy to set up on a function generator.Or, provide a square wave to an RC circuit and watch the charge and discharge time on a scope. Nothing like nailing those two equations down to a picture.I got along without an AWG for a very long time. One way or another, I was always able to come up with a signal source. It was usually pretty easy because I didn't do any analog work, just digital. Now that I have an AWG, I can use it for a lot of things that were either awkward or not possible without it.I don't think it is the first or second item on a bench but if education is part of the deal, a signal source is pretty handy to have.

author: bob91343
author_rank: Super Contributor
timestamp: April 26, 2019, 10:10:11 pm
content: Interesting idea, a lookup table and a counter. Not sure how to implement it but theoretically it seems easy.Yet, I would rather do it analog than digital.If I had a staircase generator I could cobble up a transistor curve tracer. Each step would provide an increment of base current while I would sweep the collector voltage. Or vice versa.I did build such a curve tracer back in the 1970s and used it to characterize transistors. I thought it might be fun to do it with tubes, but never went that far.Actually, I see no particular value in a curve tracer other than educational. I suppose one could match transistors that way but any circuit requiring matching seems to me poorly designed.I think I am going off topic here so I apologize.

author: rstofer
author_rank: Super Contributor
timestamp: April 27, 2019, 12:17:52 am
content: Quote from: bob91343 on April 26, 2019, 10:10:11 pmDepending on the number of samples in the waveform and the required resolution, it can be as simple as a 256x8 bit PROM (or RAM) with a counter. Or it can be done with internal memory from an Arduino.When you get the 8 bits output, you just run them into an R-2R DAC and you have an analog voltage.https://www.tek.com/blog/tutorial-digital-analog-conversion-r-2r-dacI'm not sure how to do it but I'll bet it can be done with a PC sound system.

author: bob91343
author_rank: Super Contributor
timestamp: April 27, 2019, 01:46:40 am
content: Well that's the digital way. Any ideas on doing it analog?I pulled one of my 'extra' function generators out of the closet and I see it has a VCO jack on the back. I must check the other two and see how I can make them play together.I have no use for this. It's a hobby and just seeing what can be done is an end in itself. I love playing with a TDR, for instance. I can measure coaxial length and impedance, then measure how far it is from my ham rig to the antenna terminals up on the tower. And knowing that, as well as the transmission line impedance, I can calculate the antenna impedance at the antenna. Then I can compare with a Smith chart on a VNA. Results should also agree with using a return loss bridge.So all of this shakes down to a perhaps perverse joy in owning a good electronics work bench. The OP is to be commended for wanting good gear, although he may need to do some study to learn how to use it all properly. As a matter of fact, probably all of us do, unless Fred Terman is secretly reading this.When I compare three voltmeters and they all read almost exactly the same, I smile in satisfaction.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 27, 2019, 02:30:03 am
content: Quote from: cdev on February 06, 2019, 06:18:36 amyay gol yay!

author: rstofer
author_rank: Super Contributor
timestamp: April 27, 2019, 02:47:03 pm
content: Quote from: bob91343 on April 27, 2019, 01:46:40 amSomewhere along the way, I came across a theory that ANY periodic signal can be made up of various sine waves of specific amplitude, phase and frequency.Earlier in this thread there was a link tohttps://www.eevblog.com/forum/chat/a-valentine_s-day-activity-for-your-scope-and-function-generator/msg1136847/#msg1136847This is a very cool application of an AWG. It actually has to be quite sophisticated to be capable of adding in harmonics at varying amplitude and phase.So, yes, it can be done in an analog manner but there's a reason we are using DDS instead.

author: bson
author_rank: Unknown
timestamp: April 27, 2019, 05:54:21 pm
content: Quote from: rstofer on April 27, 2019, 02:47:03 pmIf anyone reading this finds it difficult to visualize, consider the opposite which is also true: that any repeating sinusoidal can be decomposed into a superposition square waves. As the square wave harmonics added get higher in frequency the "jaggies" in the resulting sinusoidal get smaller. For the sinusoidal to be continuous an infinite number of square waves (up to infinite frequency) are needed.Exactly the same applies when trying to add up sinusoidals to a square wave. Except of course in the real world, where nothing is ever perfectly square, the Dirac delta function can't exist, and nothing is perfectly continuous (because of QM). So these are mathematical models of the real world.

author: IDEngineer
author_rank: Super Contributor
timestamp: April 28, 2019, 12:29:03 am
content: A recent "real world" use of a function generator was to test the sensitivity of the human eye to flicker when designing a multiplexing scheme for multiple RGB LED's. Read all the references you wish, you'll still be left with lots of variables. 24FPS is fast enough for old film-based movies, so that must be OK, right? Except that LED's have a faster rise and fall time. 30Hz is fast enough for LCD/LED based displays, so there you go, eh? Except that 2D arrays average differently in your field of vision than (nearly) discrete points of (nearly) monochomatic light. And so forth.So I turned on the function generator, configured it for pulse output, hooked up some LED's, got several volunteers, and varied the brightness (amplitude), duration (duty cycle), and refresh rate (frequency) as my "subjects" viewed the LED's in various ambient light levels. We learned a LOT in a very short time, and it was ridiculously easy to vary every parameter.Could I have done this without a function generator? Sure. But it would have taken a lot longer, and I wouldn't necessarily have had such accurate (and repeatable) results. I could vary frequency by single integer Hertz. I could vary duty cycle by single digit percentages. I could vary brightness (amplitude) by tenths or hundredths of a volt. All from a convenient front panel with a nice user interface and keypad. I spent my time learning and gathering data, rather than creating and fumbling about with some Rubed-up test jig.And this is just one, perhaps less obvious application for a function generator. They're also great for their usual purposes too. A scope and meter are more important, but once you have a function generator you'll likely never go without one again.

author: bob91343
author_rank: Super Contributor
timestamp: April 28, 2019, 12:37:46 am
content: So I can use the VCO input to make a sweep generator, from an external ramp wave from another generator. Not sure what limits I can get. The staircase generator is a bit more sophisticated. But I have a third generator, for whatever good that might afford.Let's see, I can run some pulses and charge a capacitor. The capacitor will go to the VCO input so I get an approximation of a staircase. End of wave could give me a reset pulse to discharge the capacitor. I would need some extra circuitry for that.