A while ago I built a Workshop Osc Machine (WOM) from bugbrand.co.uk
(schematics are here) and now I would like to retrofit his little device so I can operate its different potmeters a switches from my arduino.
My first attempt would be to retrofit the switches because I assume that I would need digital pot meters to replace/ovverrite the WOM's potmeters).
I have been googling around and I came to the conclusion that my best bet woud be to switch the WOM switch via transistor switch circuits as explained here.
Unfortunately I'm more a software than hardware guy with no real electronics knowledge.
I'm not sure which transistor would do the trick nor what value the bases resistor should have. Could somebody give this noob some pointers?
Yes that looks fine, as a basic switch, the base resistor is not very critical a 1K will do. Any general purpose NPN transistor would do, I use a BC183 but there are probably hundreds that would work in fact I can't think of one that wouldn't work. You don't need a protection diode. Use a 4K7 load resistor and connect the collector up to the input you want to ground and make the ground connection common between the two circuits.
However, looking at the schematic you have some signals (sync) that you want to pass into the circuit or not depending on the state of a switch. For this sort of thing you need an analogue switch. See:-
