In need for a function generator...

[Mint.]

Greetings!
My lab and learning process of electronics is going excellent! I now require a function generator, correct me if I am wrong, but a function generator is a generator of sine, square, triangle, etc. waves. Anyways, I have been playing around with capacitors a bit and their characteristics with different waveforms... Well just one waveform, the Rigol 1052E square wave generator, and its not enough for me anymore. I would like a selection of different waves with different selectable frequencies. My current budget would be around 200 Australian dollars.

[Rerouter]

then how about what frequencies and what waveforms? perhaps your actually chasing an arbitary waveform generator, technically a decent amount of units are just fancy named frequency generators, but actually they should be able to reproduce any waveform you program into it, with bit depth and number of samples varying from unit to unit,

[Mint.]

What I need:
- Square Wave
- Sine Wave
- Triangle

Thats about it and I'm not too fussy about the frequency...

[Mint.]

I've seen a lot of stuff similar to this:
http://www.ebay.com.au/itm/Victor-VC2002-Wave-Function-Signal-Generator-0-2Hz-2MHz-/330726130911?pt=AU_B_I_Electrical_Test_Equipment&hash=item4d00d044df#ht_2856wt_922
Are they any good?

[Teknotronix]

Just outside your budget but this is looking like an OK option:

http://www.ebay.com.au/itm/Siglent-SDG1005-Signal-Generator-Better-DG1022-/330730916381?pt=LH_DefaultDomain_3&hash=item4d01194a1d#ht_2947wt_1034

[T4P]

Hantek DDS-3x25 

[metalphreak]

If you just want to play around with different types of signals, you could combine it with some learning about opamps

http://thesignalpath.com/blogs/2011/08/21/op-amps-pwm-and-ignition-coils-tutorial/

[Mint.]

I don't really feel confident on building my own signal generator, of course I can build it, but I would not understand how it works and thats what I want to get out when I build projects to understand their operation.

[pickle9000]

This one is very inexpensive, has anyone tried it?

http://www.ebay.ca/itm/5MHz-DDS-Function-Signal-Generator-Module-UDB1102-Z-/160765044898?pt=LH_DefaultDomain_0&hash=item256e57e8a2

...mike

[T4P]

This one is very inexpensive, has anyone tried it?

http://www.ebay.ca/itm/5MHz-DDS-Function-Signal-Generator-Module-UDB1102-Z-/160765044898?pt=LH_DefaultDomain_0&hash=item256e57e8a2

...mike

Not something you want to get 

[G7PSK]

What about one of these very simple very cheap, it's a triple five chip based kit gives about one kilo hertz square triangle saw tooth and sine. I have had one for years very handy on occasions and so cheap its not worth buying the components on their own,of course if you want to play thats different but one of these any way for comparison is good idea.

    http://www.velleman.co.uk/contents/en-uk/d17_Test_Equipment.html#p31

Or one of these-

http://www.velleman.co.uk/contents/en-uk/p371.html

[FJV]

Buy a cheap opamp and put the square wave through an integrator circuit, which will give a triangle wave.

Buy a second cheap opamp and put the triangle wave through an integrator circuit, which will give an approximation of a sine wave.

I've seen some function generator circuits based on this principle on the web.
http://ecelab.com/circuit-function-gen.htm

Very likely the Velleman kit is based on this as well.

[LEECH666]

If you're ok with low end stuff you can probably built your own for a few bucks.

http://www.electronics-lab.com/projects/test/013/index.html

Florian

[caroper]

Roman Black has a great design for a low cost, 5Hz to 20KHz Crystal Locked DDS uesing a PIC18F1320.


http://www.romanblack.com/onesec/SineDDS.htm


He calls it a Sine Generator but it can do Sine, Triangle, Square and Ramp with the latest firmware.

[Lightages]

The Velleman minikit is single frequency only, and I am sure that the quality of the wave functions will be pretty low, especially the sone wave.

The Velleman hand held generator looks interesting, but at what price? It lacks duty cycle adjustments too which can be very useful.

[pickle9000]

Well I have 3 signal gens now why not 4. I just ordered this one (udb 1102). My BK 1102 is my daily driver. It's pushing 15 years but works well. I also have a VC 2002 and my biggest beef about it is the display update speed, it's really bad, signals are ok though. The last one is a Tenma something or other which is just a chinese rebanded unit, works OK but no frequency counter.

Mainly I want to try out the setting storage (save 10 settings freq, shape, and duty). If it does then I'll get another one. I often need a couple fixed sources and if I can save on setup time then that's good. I hate the case (looks like an old call display), connector locations, and the adapter will probably be toast in a month, and I will have to change any electrolytics I find.... If it turns out to be a failure I'll send it to Dave for an autopsy and then everyone can not buy one.     


http://www.ebay.ca/itm/5MHz-DDS-Function-Signal-Generator-Module-UDB1102-Z-/160765044898?pt=LH_DefaultDomain_0&hash=item256e57e8a2

BTW I can't find any reviews, or anything on this guy.

...mike

[Mint.]

Ok so I assume you people are saying that I shouldn't waste a lot of money on a function generator and make my own. I guess I am fine with that for the moment just as long as it is not too hard to build since I am still a beginner, the only downside I currently see is that it is not going to fit nicely on my bench, of course its a PCB, but it will be just lying around when I am not using it. Thats what happened to my LM317 pose supply... I have found a forum post on a function/signal generator: https://www.eevblog.com/forum/projects-designs-and-technical-stuff/signalfunction-generator/msg110422/#msg110422
what does everyone think about this one? Also I do not understand whenever it has variable frequency...

I have found one used on ebay: http://www.ebay.com.au/itm/200737227615#ht_500wt_1182
How does this one match up to the others?

[Zero999]

What do you want from your function generator?

What's the frequency range? Is it important to have a low distortion sine output? Does the frequency need to be really stable? Do you need features such as VCO and PWM controlled by an external voltage?

It's pretty easy to build a sine, triangle and sine generator with VCO and PWM control via an external voltage, using a few op-amps. The idea is to build a square/triangle wave generator VCO and use a wave shaper to get the sine and a comparator for the PWM. The frequency stability won't be great and the sine output will have a poor THD.

For a good sinewave you could use a wein bridge oscillator but that won't give you a triangle wave or PWM. The frequency stability will be slightly better than the triangle wave circuit but still not great.

The above only work for low frequencies (up to a couple of MHz or so), for RF (100kHz to 1GHz)  an LC oscillator is the best option but again it'll lack the triangle and square and the frequency stability won't be good.

If you want good frequency stability you need a crystal controlled oscillator. For low frequencies, it's probably better to go with digital synthesis, at RF a PLL is the best option.

[pickle9000]

what does everyone think about this one? Also I do not understand whenever it has variable frequency...

I have found one used on ebay: http://www.ebay.com.au/itm/200737227615#ht_500wt_1182
How does this one match up to the others?

I like the one you picked, it has all the basics.

Here is a quick description of a signal gen. I'm assuming you are a beginner with no understanding.

A signal generator makes pulses, that is that it turns the signal output on and off over and over. The pulses speed normally can be changed by turning a knob on the generator (this is the frequency (in hertz) and is the number of pulses in a second). The level (voltage) of the signal can also be changed (normally with a knob). Most signal generators allow you to change the shape (a scope is the easiest way to understand that part). Normally you would like to have square, sine and triangle for your shapes. A very nice feature to have on a signal generator is a frequency counter. This will allow you to quickly see how fast the pulses are coming. If you have a scope you can either calculate this manually or use the built in frequency counter if it has one. A voltmeter on the output is also useful.

What do you need it for?

- tricking equipment into thinking it is hooked up to something when it's not
- evaluating the performance of amplifiers (of any sort)
- designing filters and much more.
- if you are getting a scope and have a signal generator, it's the safest way to learn about the operation of an oscilloscope and worth every penny just for that one purpose.

...mike