Relay Control PCB

This is my first PCB design. It’s a circuit for controlling the operation of small signal relays of the type you commonly find used in guitar pedal bypass circuitry, but with a few semi-fancy additional features I found I wanted but couldn’t find in any of the available commercial/DIY kit options.

These are:

- The option to connect switches to control both/either latching (press once -> on, press again -> off ) and momentary (only on when switch is pressed) behaviour.

- The possibility of connecting both momentary and latching switches, so that the momentary switch will always invert the current state. This means that when the latching switch is off, the momentary switch turns the signal on, but if the latching switch is on, the momentary switch will turn the signal OFF.

- Space for two DPDT relays on each board, which allows true bypass switching of stereo effects

- Expansion headers so that it’s possible to chain up multiple boards to be controlled by the same switch - for the rare occasion you want to switch up to 12 individual signals with one switch.

- Despite all this, to still be small enough to fit easily into mini DIY pedal builds.

It was also a good opportunity to learn how to solder surface mount components, both by hand, but also in a “DIY reflow oven” (surface top toaster over):

Me first ever surface mount reflow experience on me first ever pcb design. LOOK AT IT GO SHINY pic.twitter.com/RgX32oBkwm

— Mike Parr-Burman (@empeeby) March 25, 2017