I finally got my prototyped Pi printer shield baked. By no means is it perfect, but here are the features:
- input voltage designed for 12v-24v, has a voltage regulator to push 5v to the Pi (no USB power). Pretty good power conditioning.
- Relay connected to a GPIO pin. Connected through an optocoupler, so you can safely switch your printer with it.
- Four GPIO-switched FETs, lowside-driven (so, switches ground on/off, use whatever voltage you want, probably the 12/24v). Designed for 2A max, has overcurrent, overtemperature, overvoltage protection.
- On-board temperature sensor (good for environmental sensing).
There's also a provision for a fan controller and 3-pin fan port, but I haven't connected those.
I'm going to build and test a couple of these, and I have the next design already in the hopper. I've simplified some of the parts and made it so I can surface-mount solder everything -including the big capacitor, the 2x20 pins for the Pi, the screw terminals, and so on. Those add a lot to the cost (about $10), so I have it set up to also have the proper holes if someone wants to finish up the soldering themselves and save some money.
This is designed for Octoprint; I somewhat assume there's enough interest that I could do a small run of them- my minimum goal is about 8 boards. A board will cost about $20-40 depending on how well the pricing works out- it's not intended to be the cheapest way to get the job done.
So, if you're interested, what features would you like to see added? 5 fan controls? SSR drivers? High-power LED drivers (with an off-board connector)? Thermocouple/thermistor inputs? Off-board temperature/humidity sensing? LED indicators? Panic shutdown switch?