Should I get a function generator? - Page 1
Forum section: electronics / beginners

author: int2str
author_rank: Regular Contributor
timestamp: February 17, 2015, 06:20:06 pm
content: Ordered my first ever oscilloscope (DS1054Z; yay!).Now I'm highly contemplating also buying a function generator.Dave points them out in his "how to set up a lab video".My background:- Software engineer by trade- Hobby level hardware tinkerer- Have created a few PCBs; even sold oneWhat I want to do:- LEARN- main reason I got the scope- Teach my son....- Be able to debug/fix circuitsWhy I think I "need" the function generator:- Ability to generate functions will make learning [the scope] easier- Ability to generate PWM and other waves will allow me to debug circuits / test servos etc.Why I think I DON'T need the function generator:- Could probably use an Arduino to generate any functions I may need. Not as adjustable, but would probably work. Don't need high frequency (famous last words) or accuracy for what I do.Soooooo......I put off buying the scope for too long. It's an immense learning tool that I should have picked up sooner.Is a function generator of equal "must have" value or is it a "have one; rarely use it" kind of think for you?Thanks!

author: mentaldemise
author_rank: Regular Contributor
timestamp: February 17, 2015, 07:00:02 pm
content: I was wondering the same thing. I'll be interested in what people think. I have mostly the same background as you, and am just starting! I did buy a cheap little kit that I think does the Arduino thing for you:http://www.ebay.com/itm/261603309142?_trksid=p2060778.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITMight be crap, dunno, haven't gotten it yet. For 13 bucks, couldn't hurt to get the soldering practice at least!

author: tggzzz
author_rank: Super Contributor
timestamp: February 17, 2015, 07:08:05 pm
content: Quote from: int2str on February 17, 2015, 06:20:06 pmI have just got my first, 45 years after starting doing electronics. But that is misleading since for the latter 35 years I used my employers equipment.QuoteIf you use your ingenuity, you don't need one - but they can be convenient.The major decision is what signals you want to generate - and that depends on what you want to test.The first distinction is analogue vs digital. If you are building analogue equipment then a square/sine function generator or arbitrary waveform generator is appropriate. If you are building digital equipment then a multi-channel pattern generator is appropriate. If you are building RF equipment, join your local amateur radio group

author: nadona
author_rank: Regular Contributor
timestamp: February 17, 2015, 09:54:49 pm
content: I think function generator is one of the basic equipments in a EE's lab.MYpriority: 1) DMM 2) Oscilloscope 3) Power Supply 4) Function Generator 5) ....

author: old gregg
author_rank: Regular Contributor
timestamp: February 17, 2015, 10:11:28 pm
content: I think it's quite essential to have, at least, one fonction generator.I know that for audio purposes I couldn't live without. But it also proved itself for debugging the wrong fuse setting on my AVR.Don't need to spend large money on it, you can find cheap one for 40/60 euros. I have a Thurlby Thandar something which I'm very happy with.A standard, general purpose is a good start. You can then decide, depending on your need, to buy a more specific one.

author: VK5RC
author_rank: Unknown
timestamp: February 17, 2015, 10:27:22 pm
content: I would get 2 dmms and 2 power supplies and possibly a frequency counter before getting a function generator, based on what I actually switch on.

author: rdl
author_rank: Super Contributor
timestamp: February 17, 2015, 10:35:10 pm
content: I can agree with that. Multiple DMMs and power supplies are often in use here. Heck, I have an IET Labs capacitance substituter that gets used more than either of my function generators. They are kind of cool looking to have sitting on the shelf though.Quote from: VK5RC on February 17, 2015, 10:27:22 pm

author: AG6QR
author_rank: Frequent Contributor
timestamp: February 17, 2015, 11:01:34 pm
content: As in many of these things, it depends on what you want to do.I have almost the same background as int2str (software engineer by trade, some hardware education and lots of hobby level hardware tinkering). As some might recognize from my forum handle, I'm a ham radio operator (AG6QR is my call sign).I find that some sort of function generator or at least some sort of variable oscillator is virtually essential for tinkering. You may not need a professional instrument, though. You can lash up your own oscillator using a Wien Bridge for sine, or using a 555 for square; there are other options for specific types of home brew oscillators. But a purpose-built function generator makes things easier.I have used an antenna analyzer as a function generator. An antenna analyzer is a specialized device for radio use, which generates a low power sine wave at a radio frequency, and then measures the response of an antenna system. It's not a great general purpose function generator (sine only, voltage not adjustable), but it's a very useful instrument for any ham radio operator, and the fact that you can find other uses for its radio frequency oscillator is a free bonus.I've got an Elenco FG-500K, a very inexpensive kit based off the XR2206 IC. It works, and there's lots of information about it on the web. It's not a great piece of gear -- its output has a significant DC offset that isn't adjustable, its sine output has significant distortion, and the output impedance is closer to 600 ohms than 50 ohms. It can oscillate as fast as 1MHz, but its amplitude isn't well-controlled --it drops considerably near the higher frequency range. Its going price of around $30 to $40 makes it hard to complain about its deficiencies, but I consider it more of a toy than an instrument. It's a step more convenient than building your own homebrew oscillator from junk box parts.I also have an GW Instek SFG-1003. This is a nice DDS generator, basic and not high end, but it offers very stable crystal-controlled frequency output, controlled 50 ohm impedance, variable duty cycle square waves, adjustable duty cycle, adjustable DC offset, adjustable voltage, etc. Up to 3MHz output for sine and square, 1MHz for triangle. No modulation, but I've tacked on a simple homebrew AM modulator which does that trick. This is a genuinely useful instrument, but it still lacks sweep or FM modulation, and its frequency range isn't as good as other options. Its going price is around $150.

author: jobog
author_rank: Regular Contributor
timestamp: February 18, 2015, 04:10:13 am
content: Quote from: mentaldemise on February 17, 2015, 07:00:02 pmI was thinking about getting this same kit off of ebay just to play around with with my scope. How do you plan on powering this thing. It needs +5V and + and - 12V. I thought about using an old computer power supply. Looked around for a circuit to build something supplying those voltages but the cost of a suitable center tap transformer is more than a computer supply.

author: lapm
author_rank: Frequent Contributor
timestamp: February 18, 2015, 01:59:01 pm
content: Have you considered building simple function generator yourself, just to get you started? You can get nice DDS modules from ebay.I sometimes use one that claims maximum frequency output of 40 MHz, but to be on safe side i assume max of 10 MHz. Good enough for me for now.. After i get scope, i'm sure i will start miss more quality then something hacked together quickly...

author: Yago
author_rank: Frequent Contributor
timestamp: February 18, 2015, 02:35:16 pm
content: Quote from: VK5RC on February 17, 2015, 10:27:22 pmCan I ask, what are the uses for counter?Guess that radio plays a part for you. but thinking I am missing a trick or two here.

author: plazma
author_rank: Frequent Contributor
timestamp: February 18, 2015, 02:40:06 pm
content: Quote from: Yago on February 18, 2015, 02:35:16 pmMeasuring exact crystal frequency. Fine tuning RTC crystal capacitors etc.

author: Yago
author_rank: Frequent Contributor
timestamp: February 18, 2015, 02:45:55 pm
content: Quote from: plazma on February 18, 2015, 02:40:06 pmI kinda suspected those, funnily enough used to work in a quartz crystal production facility!Just wondered if there was some more esoteric tricks, eg confirmation of activity on a bus that is way beyond your scope's bandwidth.

author: timb
author_rank: Super Contributor
timestamp: February 18, 2015, 02:46:28 pm
content: Quote from: plazma on February 18, 2015, 02:40:06 pmThough, for most beginner uses a modern scope will get you to 7 places measuring frequency. More than adequate for most needs unless you do RF.As for a function gen, I use mine multiple times a week in general analog and digital circuit work and consider it a huge luxury.Sent from my Tablet

author: tggzzz
author_rank: Super Contributor
timestamp: February 18, 2015, 02:58:52 pm
content: Quote from: timb on February 18, 2015, 02:46:28 pmIs that 1 part in 10^7 resolution, repeatability, accuracy? How does it achieve that, other than by having an internal frequency counter?

author: Yago
author_rank: Frequent Contributor
timestamp: February 18, 2015, 03:16:48 pm
content: Actually, wouldn't the act of probing a crystal oscillator throw the frequency off?Used to have to go to some lengths to measure crystals back in the 80's, jigs to compensate for capacitance and resistance were used on adjust stage, but absolute measurement was on a very expensive bridge.The calibration block of gold alone, was enough of a financial shocker.

author: Corporate666
author_rank: Unknown
timestamp: February 18, 2015, 05:06:31 pm
content: To the OP:In my opinion, hold off on a function generator.I use mine rarely... it's one of those things that when you need it, you need it... but it's pretty easy to set up any of a multitude of dev boards to output what you need usually, unless you need arbitrary waveforms of customizable waveforms. But if you needed any of that, you would know you needed a function generator and not be asking hereIf/when you have the itch to get one, I recommend one of these:http://www.ebay.com/itm/10MHz-DDS-Function-Signal-Generator-Module-Sine-Triangle-Square-Wave-TTL-SWEEP-/321157000855?pt=LH_DefaultDomain_0&hash=item4ac672ee97(or similar). I have a nice Fluke FG at work, but I have that little one at home and it's perfectly fine for the occasional time at home I need to generate a signal.

author: AG6QR
author_rank: Frequent Contributor
timestamp: February 18, 2015, 05:29:40 pm
content: QuoteNot sure about exact specs, but many modern DSOs have an internal frequency counter with accuracy governed by the scope's internal clock. The counter counts the scope's trigger signal. I know the Rigol DS1052E has this feature.

author: tiltit
author_rank: Regular Contributor
timestamp: February 18, 2015, 05:52:17 pm
content: I am sure there is a lot to learn from building a function generator. I myself am planing to build one using a ICL8038, should be quite cheap and very instructive.

author: timb
author_rank: Super Contributor
timestamp: February 20, 2015, 11:54:00 am
content: Quote from: AG6QR on February 18, 2015, 05:29:40 pmYup. It generally only applies to the trigger.Here's an example; notice the trigger frequency (triggering off CH1) is 10.0001MHz while the CH1 measured frequency is only 10.00MHz.Sent from my Smartphone

author: tggzzz
author_rank: Super Contributor
timestamp: February 20, 2015, 01:56:17 pm
content: Quote from: timb on February 20, 2015, 11:54:00 amIgnoring for a moment my important caveat "other than by having an internal frequency counter", I'm afraid that, on its own, that's not convincing. But then I'm picky because I know of at least one (very expensive) attenuation test set that had aresolutionandrepeatabilityof 0.001dB, but theaccuracywas only 0.1dB, i.e. 100 times worse. The accuracy wasn't important since the customer was interested in changes in attenuation (over time and temperature), not the absolute attenuation.I could dream up several scenarios, e.g. the measurement being quantised in 1MHz steps and with the 0.0001 being a result of sloppy arithmetic! Now I strongly doubt it is that extreme, but if there isn't an internal frequency counter I'd like to know how it is done.Does the manual have any specification for the frequency display's operation, resolution and accuracy?

author: AG6QR
author_rank: Frequent Contributor
timestamp: February 20, 2015, 05:36:40 pm
content: Quote from: tggzzz on February 20, 2015, 01:56:17 pmIn the scopes we were discussing, there IS a built-in frequency counter, which counts the trigger pulses.There's also a way of measuring frequency by looking at the display and measuring the distance between repeating waveforms, but that's not nearly as precise or accurate.I'm not sure which manual for which scope you're asking about, but the Rigol DS1052E manual only mentions the counter in the section where it tells you how to turn it on and off via the utility menu. There is no specification for its operation, resolution, and accuracy. I don't have a good way to calibrate it to a standard, but I do know that it has been consistent with my function generator's frequency display to five digits, which has been good enough for my meager purposes.Of course any counter's absolute accuracy and stability is going to be limited by its clock. Many lab grade oscilloscopes have a provision for an external 10.000000 MHz oscillator input, which can be provided by a rubidium standard, or whatever, to improve the timing stability and accuracy. My cheap Rigol DS1052E doesn't have this feature, but it's common on higher end DSOs.

author: tggzzz
author_rank: Super Contributor
timestamp: February 20, 2015, 06:32:32 pm
content: Quote from: AG6QR on February 20, 2015, 05:36:40 pmThat's all perfectly understandable. The difference between those two measurements is precisely what I was expecting, but (I suspect) was not clearly enough stated for the OP to understand.QuoteAgain, all perfectly understandable if you are using a frequency counter - but not if you are using a scope. It is no use buying ascopeto make accurate frequency measurementsunlessthere is also a separate frequency counter buried inside the same case - which won't, in general, be true.

author: AG6QR
author_rank: Frequent Contributor
timestamp: February 20, 2015, 07:28:46 pm
content: Quote from: tggzzz on February 20, 2015, 06:32:32 pmGranted, it wasn't true of many old analog scopes.But are you aware of a currently manufactured digital scope that doesn't have a frequency counter buried inside the same case? I figured that if it's a standard feature of the bottom of Rigol's line, it's probably on most other maker's scopes, as well. I just checked some users manuals, and the $290 Owon SDS5032E has it, as does the $280 Siglent SDS1022DL. So does the $340 GW Instek GDS-1072A-U. These are not high-end scopes.I went back over the thread, and the only place I see someone claim that a scope is good for accurate frequency measurements, they've qualified that by saying a "modern" scope.

author: janaf
author_rank: Frequent Contributor
timestamp: February 20, 2015, 07:46:05 pm
content: QuoteYou have a basic low frequency function generator in the PC sound output if you combine with suitable software. There's a lot of freeware that generate sinusoidal, triangle, square, white noise, pink noise, dual signals, phase shifts, variable duty cycle etc. Not the real thing but gets you started.

author: tggzzz
author_rank: Super Contributor
timestamp: February 20, 2015, 08:00:01 pm
content: Quote from: AG6QR on February 20, 2015, 07:28:46 pmThe last time I bought a 1GHz 40MS/s scope, it didn't. But then HP's philosophy was that the instrument should do one thing well, rather than gain "marketing festure" brownie points by doing two things less well.

author: jamesd168
author_rank: Contributor
timestamp: February 20, 2015, 09:20:30 pm
content: Quote from: AG6QR on February 18, 2015, 05:29:40 pmwow, these things are really inexpensive.

author: guygibbs
author_rank: Newbie
timestamp: February 20, 2015, 09:58:50 pm
content: I'm not sure if this helps well actually I'm sure it won't but I'm a newbie and I have recently built an arduino & 386n-1 triangle square sawtooth and sine generator and have yet to use it haha but high insight I got an android app that worked from the start and is very useful and I didn't have to troubleshoot anythingalthough that is where the learning comes in most . So if you just want to get some signals on screen and learn scope go with the app. If you need more than 2v. Then build one or of course purchase as needed ! Just my 2cents

author: Lightages
author_rank: Unknown
timestamp: February 20, 2015, 10:14:33 pm
content: I have been mulling over this need or want for a function generator. Some people have already made the statement that two mulitmeters would be a priority over a function generator. I would tend to agree The order of importance to me would be:1: Two multimeters of good quality2: Oscilloscope3: Dual rail adjustable power supply4: Function GeneratorThis is all according to what you are actually working on however. If you need a function generator then a second multimeter does you no good. The best is to have all four of the above as a minimum. Perhaps a sound card output can function for what you need, but only up to audio frequencies. For many people that is enough.So the grey area wishy washy answer is "It depends". If you need a binary answer, then "Yes you should get a function generator".

author: timb
author_rank: Super Contributor
timestamp: February 21, 2015, 06:10:40 am
content: Quote from: tggzzz on February 20, 2015, 01:56:17 pmThe trigger circuit is generally a lot more sensitive and higher resolution than the actual inputs of any given scope. Take for example my Tek MSO2024B; the trigger goes up to 500MHz whereas the scope's bandwidth is only 200MHz.When you think about it, a trigger circuit is just a frequency counter without the counter. On a DSO it's dead easy to count the trigger pulses digitally. Thus you get a high resolution frequency indication free of charge.It's not some bloaty added feature. It's just how the scope works.Sent from my Smartphone

author: alterbaron
author_rank: Contributor
timestamp: February 21, 2015, 09:23:34 am
content: Quote from: int2str on February 17, 2015, 06:20:06 pmDepends on what you want to build / test / learn about.For tinkering with analog circuits (amplifiers, filters, .etc) a function generator is an indispensable tool.If you're working mostly with microcontrollers and digital logic, it may be less useful.Basically, having a function generator saves you the trouble of having to build an oscillator every time you wish to inject a signal into your circuit.If the price of the function gen is lower than the hassle of rolling your own oscillator every time you need one, then pick one up.

author: Amra
author_rank: Contributor
timestamp: February 21, 2015, 11:35:43 am
content: You could always make one as a project, maybe use the XR2206 chip. The chip only costs around 8USD, and there are plenty of open source circuits floating around for making a pretty good generator with it. Depending on what you have in your parts bin, the whole thing could cost you next to nothing.They are quite useful, depending on what you do. Signal injection/tracing is quite useful for diagnosing circuits that aren't working, you can also use them to find out what kind of transformers you have in your parts bin or salvaged ones (i.e. their turns ratio), you can use them to for comparing audible signals, or as a temporary oscillator/timer while prototyping, you can even use them to test things like LC filters. I'm sure there are a lot more uses, those are just the ones that came to mind.