Simple DIY function generator board

In sorting through a bunch of old chips I found a couple XR (exar?) 2206CP function generator chips. I decided to build a small generic circuit around them to make them useful. Even though there are a few different ways to use this chip I settled on a pretty common use with some tweaks for my preferred component form factors and completely ignored the footprints for the potentiometers because it’s my intention to put this board in a small enclosure with switches and knobs for control (panel mount, not board mount).

This is a pretty simple circuit, but I added a couple things because I could.

So, the mechanical decisions were pretty standard. I use M3 holes and round the corners in kicad centered around that hole. I used a standard barrel jack for 12v power in the back, and footprints for components I had on hand. I like using 0603 for passives, either to-92 or sot-23 for transistors, and that little 1117-5 regulator (I prefer these over 7805s these days). You can also see that the jumper positions were placed for layout ease and not for ease of operation because this is for use in an enclosure. I have completely random sizes of electrolytic capacitors so those footprints don’t matter so much, and I really like these hook test points for clipping on to (but why do manufacturers have gator clips and not micro grabbers for scope probes?).

This is the standard square wave output drive circuit I’m using. It’s running through a npn transistor.

This is the circuit I added, I’m using a TTL nand gate as an inverter because I had one. That lets me have a TTL level driver for circuits that would like it. I also used the second one to add an inverted output to it so I now have both signals out of phase from one another, I could envision some uses for that.

it works!

Almost surprisingly it all works the first time. I have two of those function generator chips so I think I’ll build at least one in an enclosure for my own use. I may build up a second one as well to use up an enclosure and one of these chips, maybe not. If you want a pcb, just say so and you can have one of my spares, or maybe one of my spares and the spare chip I have too. If you want to make your own or hack on my design to add a different layout or output stage the designs are up on github here.

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