Pi hat for printer power, relays, MOSFETs, etc


I've set up a couple of printers this week, and it made me dislike my cobbled-together octoprint accessories. So I spent an excessive amount of time researching decent components to make a good helper HAT. Here's what it has:

  • 12v+ input on screw terminals (24v should be fine, this applies elsewhere in the list)
  • buck converter to take this input power and make a nice 5v 3A power supply for the Pi
  • onboard I2C temperature chip
  • optocoupler+relay to provide general 12v power (intended for the PSU control plugin)
  • four I2C-driven lowside MOSFETs to provide power to bigger loads
  • 3-pin 5v I2C fan control with tach (actually, this is a fully designed placeholder, chip isn't being made yet)

I'm ordering enough chips to make a few. It isn't cheap (BOM is about $20ea plus jellybeans plus the board plus building it and the risk that it might not even work), but I thought I'd share it here.

Now I just need to finish writing the PID code for my SMD toaster oven so I can use it again.


I think the URL would be helpful it it more directly goes to the info for this (or you add a prominent link up there on the landing page).

My printer runs from a beefy 24V brick, for what it's worth. It replaces the standard laptop 19V brick that a lot of the printers are using.


Yeah, I use 24v too. I made sure everything is rated for either.

I use my generic tedder.me URL as a placeholder because it's more than just my name, though much less than if I were making kits or anything from this.

I'm still stewing on how to run power to my printers. Right now I'm using N+1 PSUs; the last one runs LEDs and Pis. I'll have to take a pic of my MP Mini Delta hack that led to this board.


You might look into those cool, new PSUs like you'd find for a mining rig. They usually come with lots of those chunky 8-pin connectors which push a fair amount of 12V.


I have one- and a breakout board- mounted to my wall. I was using it until I converted my E10 to 24v, and then I was using three power supplies. Got a little nutty.

They are great for pushing 12v. I should use it to power my Pis and my MP Mini Delta, since it is 12v anyhow.

Here's the PSU mounted on the wall, and here's the little ATX breakout board. It's a great way to go because you have always-on 5v.


Yeah, that's exactly the PSU variety I was suggesting. Just be careful on the wire gauge coming off that; it looks a little small to my eye.

I owned/operated my own datacenter at one point (hosted websites/databases) and I had lots of DC adapters of every shape and size up in "the zone". So I ended up buying a big Radio Shack industrial-sized 12V adapter and used some big honking resisters to create voltage ladders down to 6V and 3V and then created 12V, 6V and 3V buses for same. I then used those little customized 2-pin ends for their universal adapters (AdaptaPlug). It worked out great.

Ultimately, an accumulation of individual DC adapters wastes more energy than one large adapter.

My original suggestion was to use the GPU cabling connections to feed your 12V needs. They're beefy enough to get the job done.

Just found this, thought it was cool and you'd enjoy.


That was 5v for Pi and the trigger wire.


I might have to buy one of those from you when you get them going. Let me know.


Yeah, I chose the other variety of breakout because I liked the form factor better.

Oh- and:

I soldered/heatshrinked the GPU cable to join all the wires together and fed that into my external MOSFETs.