"Function Generator" by Forrest Mims

[iampoor]

In one of Forrest Mimms mini-notebooks, this circuit was published



I havent built it in a long time, but I recall the sine wave output amplitude not staying consistent over the tuning range. Does anyone know of a circuit with square triangle and sine wave outputs that doesnt have that issue? I want to build a drone oscillator with 6 of these with selectable waveforms 

In essence...is there an adjustable signal generator circuit that can output sine, triangle, and square waveforms at equal amplitude and be made with 1 or 2 quad opamps? I feel like I have seen this before, but cannot for the life of me remember where!! AM I going nuts?

[slacker]

If you want something simple have a look at the LFO from the Easy Vibe this uses diodes to clip a triangle into a sine. Or have a look at some diy synth VCO schematics for for other ways to do it.

[merlinb]

You could cheat and use a function generator IC like the ICL8038 or XR2206...

[iampoor]

If you want something simple have a look at the LFO from the Easy Vibe this uses diodes to clip a triangle into a sine. Or have a look at some diy synth VCO schematics for for other ways to do it.

I like the easy vibe LFO but I can't get the 3 waveforms out of it, similarly I haven't found a relatively simple synthetic LFO with those 3 output waveforms. I am either missing something or looking in the wrong places or have wrong expectations. As its almost 4am here....I'm going to go to bed because I'm sure the answer is obvious. 

You could cheat and use a function generator IC like the ICL8038 or XR2206...

The icl8038 is a candidate, I'm just worried about sourcing such an old part...I have some friends who are keen on my idea so atleast 10 units will be built. I am concerned that ebay sellers might be selling fakes or poor performing chips. But I ordered a pair, it would be nice if they work, since they are so cheap and don't need many external parts!

[garcho]

check out Ken Stone's Utility LFO:

http://www.cgs.synth.net/modules/pic/schem_cgs58_lfo.gif

[slacker]

I like the easy vibe LFO but I can't get the 3 waveforms out of it,

You can get all three wave forms out of the easyvibe LFO, Looking at this schematic http://www.hollis.co.uk/john/easyvibe.jpg the output of the opamp that connects to the 22k resistor and the depth pot is a triangle. The output of the opamp that connects to the rate pot is a square. The wiper of the depth pot is a sine, it's a lower level than the other two waves but you can use an extra opamp to boost it up to the same level.