I’m working on a module idea for a friend which is basically a collection of attenuverters, each with a button. Each one can be dialed to a different voltage, and when the button is pressed it delivers the voltage it’s set to, to a single output. When the button is pressed and the voltage delivered, an LED lights up. Right now the circuit in my head looks like this:
Voltage in > button > attenuverter > voltage out
I’m just having trouble figuring out where in the circuit to drive the LED. So far I’ve considered:
- Driving the LED with a transistor after the button but before the op-amp
- Driving the LED with a transistor after the op-amp but before the output impedance resistor (prob won’t do this since the output from the op-amp could be positive or negative)
- Putting the LED in the (negative) feedback loop of the op-amp [ dunno if this will work, if I need a PNP transistor driving it here or what ]
The module will be running on standard eurorack power (+/-12v) and I’ll be regulating a 5v supply as well, which is what will be going to to the attenuverters, to give a +/-5v output. Right now my intention is to have the LED light at a constant brightness, though an option to have it light relative to the level of the attenuverter would also be welcome (I figure this would go on pin 2 of the pot, between the pot and the +input of the op-amp?).
Anyway, it seems a pretty straightforward circuit, but the LED is what’s tripping me up. Any help is greatly appreciated.
Editing to add: I’m basing the attenuverter circuit on this one from Skull & Circuits. It’ll be taking 5v at the input (where the jack is in the diagram, obv) so I may need to change the resistor values, I know. I’ll figure that out in due time.