Stec Records - EH16 Switch Page

Electro Harmonix came up with this very clever scheme for reading the switches on the unit itself and also for a remote foot controller. You start with a power supply voltage. Each switch is connected to a resistor connected to a summing node at the input of an A-D converter. The other side of the switches are connected to ground. As each button is pressed the voltage at the input to the converter changes relative to it's resistor value. The clever part is that they worked out the resistances so that the each switch changed the voltage just enough to toggle a specific bit of the converter output. It seems like a lot of trouble for nothing but it allows you to have a bunch of switches on the remote with only a 1/4" guitar cable connecting them. Very cool. No special cables. I like it.

A bitch to troubleshoot though. If you are pressing a switch on the main unit and the corrisponding AD output is not toggling, chances are the AD is bad (assuming you have already checked the supplies). Luckily the AD is an ADC0804 which is fairly easy to find (see Parts).