Huvud 3D Printer toolhead board

A very small 3D printer board for use on a toolhead. It is designed to be used with Klipper firmware.

Features:

TMC2209 driver
STM32F042C6T6
Two MOSFET drivers fans
One bigger MOSFET driver for a hotend heater
Thermistor input
One endstop
CAN bus

Main power is 12-24V. 24V is preferred to keep the currents low

The CAN Bus is not terminated, instead it uses 4 wires, termination should be done at the other end.

It uses an external 3.3V switch regulator.

All done in KiCad

Possible issues:

Is the cooling for the TMC2209 adequate? Seems to be, the board reaches about 50C under the TMC2209 when running a small stepper at 1A.

Change ideas:

Is the endstop useful? Could be used as a filament runout sensor.

2020-05-18:

First prototype production run is done.

The board works mostly as intended. Some quick tests shows that the MCU can run klippy, stepper drivers, fan drivers and thermistors works perfectly fine.

2020-05-29:

After a lot of software work and many hours of testing I can report that everything actually works as intended (except one resistor that should have been 1k was a 10k)

The thermistor input gives a very low noise signal, even at high temperatures.
Endstop works
All mosfet outputs works with reasonable loads (2A at 24V). I do not have a dummy load for very high load testing, but a heater on the FAN connectors and a hotbed to the heater connector...
The thermals of the TMC2209 seems ok. With no cooling fins or active cooling it reaches 60C (top and bottom) when mounted close to a hot stepper. I should test with a larger stepper (>1.5A) in a hotter environment to see when the TMC shuts down. I am considering a different fab that allows thicker copper layers for better heat spead, and better power margins.
The CAN bus works good after some software work. It should work fine with up to 8 nodes on each bus, possibly more. I have run 4 boards on the same bus, each with one stepper, simulating a complete 3D printer.

It is possible to fit different connectors for most functions. It is designed for mostly angled JST-XH or screw terminals but it's possible to fit straight connectors or other 2.54mm for most functions. JLCPCB do not mount through holes so the boards come without connectors. For a larger (>30) production run the boards would have to be panellized, which looks like a non-trivial task with KiCAD. If anyone has experience and wants to help ...

As a sub project to this board I have developed a little power and CAN distribution board combined with an STM2515 CAN bus controller in the form of a Raspberry Pi Hat. It is a very simple little board but has turned out to be very valuable. With some more thought put into it I think it will be a good complement to the Huvud tool board. It has to be modified to allow it to be used separate from a Pi with a different CAN controller. It also needs some fuses, a proper isolated CAN tranciever, more flexibility for the CAN termination and connectivity. A an option to fit a voltage regulator to power the Pi from the boards power. And mosfets to power down the boards ... feature creep...