How to add input LED to Kassutronics ASR

[Jos]

I was trying to point out 2 possibilities: 1 to add some signalling for the input and to the Schmitt trigger and 2 to make it suitable for positive and negative voltages. One led + series resistor from the op-amp to -Vcc and one led + series resistor from the same output to +Vcc. If you want to avoid the dark void between -U forward and +U forward you could go for a bit more complexity as I’ve used in Pedal-O-Matic, which looks nice, but may be a bit much:

@Jos

I added the two extra opamps (with 4 of them in a TL074, this requires one chip per pedal). What they do is they take Vout as input and a voltage set by a trim pot, so that the green LED lights up as soon as Vout gets higher than 0 Volts (by adding exactly the 2.7 Volts needed to light up the LED) and the yellow LED lights up as soon as Vout goes below zero Volts. When calibrated these opamps take care of a smooth transition of the light of the LEDs around 0 Volts ( about the pedals center position ).

See Pedal-O-Matic foot pedal module - #2 by Jos