The pedal is a Boss FZ-5 and, like most Boss pedals, uses a momentary footswitch. This makes it simple to bring out the switch's contacts to a socket, allowing a remote footswitch to be connected in parallel. But it also seems useful to have an LED on the remote that confirms the pedal's on/off state. This is more difficult to achieve as you can't just connect an external LED in parallel with the internal one. A buffer circuit is needed:
LED_IN connects to the FZ-5's LED anode. When it is off, no current flows into the base of Q1, so R4 pulls the base of the U$1 to 9V, turning it off, so no current is supplied to the external led via LED_OUT. When the internal LED is on, Q1 and U$1 are turned on, supplying current to the external LED via R3.
This circuit could have been fitted on Veroboard quite easily, but I wanted to get more experience with assembling surface mounted components, and fancied the challenge of making the board as small as possible. The final layout is 17.5mm x 3.5mm:
It's double-sided and will fit inside the pedal easily, enclosed in heatshrink.
Assembly:
Connecting to the 9V supply at the power socket:
Connecting it up inside:
The remote footswitch is connected through a stereo mini-jack socket:
Done:
The remote footswitch:
Demo:
