98 lines
5.1 KiB
Markdown
98 lines
5.1 KiB
Markdown
# Huvud 3D Printer toolhead board
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A very small 3D printer board for use on a direct drive toolhead. It is designed to be used with Klipper firmware.
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Klipper has the awesome feature to be able to use multiple MCUs connected to the host over a (relatively) high latency connection. Using CAN bus it is possible to chain many boards using just a pair of twisted wires and power. A good solution for multiple head 3D printers.
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Features:
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* CAN bus.
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* One TMC2209 stepper driver for the extruder
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* Two MOSFETs for fans
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* One big MOSFET for the hotend heater
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* Thermistor input
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* Support for an endstop (or filament runout sensnor)
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* STM32F103 72Mhz MCU
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* USB, for flashing firmware
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Main power is 12-24V. 24V is preferred to keep the currents low
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All done in KiCad and open source.
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If you are interesting in helping out, testing or eventually using this board feel free to contact me at glpontus@gmail.com.
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### Documentation
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* [Pinout and hook up](doc/pinout.md)
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* [Klipper configuration](doc/klipper.md)
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* [CAN bus](doc/canbus.md)
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* [Prototype versions of the board](doc/versions.md)
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---
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## 2020-05-18:
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First prototype production run is done.
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They work!
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---
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## 2020-05-29:
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After a lot of software work and many hours of testing I can report that everything actually works as intended (except one resistor that was a 10k insteadof 1k)
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* The thermistor input gives a very low noise signal, even at high temperatures.
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* Endstop works
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* All mosfet outputs works with reasonable loads (2A at 24V). I do not have a dummy load for high load testing, but a heater on the FAN connectors and a hotbed to the heater connector...
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* 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.
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* 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.
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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.
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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 ...
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---
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## 2020-06-10:
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Version 0.4 is almost complete.
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* It has an on-board 3.3V regulator replacing the external board. (Quite a challenge for an old SW engineer using JLCPCB's very limited selection of components)
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* Thermistor connector moved down next to the fan/heater connectors
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* Lower profile capacitor for the stepper driver, it was very tall.
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* Debug header moved and extended. BOOT1 exposed.
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* Serial pins removed, not very useful anyway
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* Fan/heater connectors tweaked to be able to fit JST XH, screw terminals or Molex KK connectors.
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* Added a micro-USB connector for easier flashing and possibly other features. The board is not powered from USB.
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* Switched to an STM32F103. Mainly to allow for a proper bootloader and flashing over USB. Or even over CAN if I develop a custom bootloader. With many boards it would be very nice to be able to bulk flash them all at once over CAN.
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I have done thermal stress testing of the board. It can run a big stepper at 1.5A, board attached very close to the hot stepper with no forced airflow and 25C ambient. The driver reaches 90C (measured with a probe) but does not shut down due to overheating. The entire board heats up as designed to act as a heatsink, most inner and outer copper layers are groundplanes to spread the heat.
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I'll very soon order another 20-30 board to send out to brave beta testers.
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---
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## 2020-06-24
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Ready to manufacture some more prototypes
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Among many small tweaks the heater mosfet is changed to a different one with better Rds at 3.3V Vgs. If I limit the board to 24V and a 40W heater it could use the same small mosfet as for the fans.
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Unfortunately JLCPCB are out of TMC2209 so I'll have to find a different prototype house that has them available. Perhaps one with 2oz outer copper layers for better thermals.
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CAN bus is surprisingly robust. I have tested it through a 50m roll of ethernat cable, various sketchy test setups with star networks, breadboards, close to EMC sources etc. It always works. The Bosch engineers did a good job almost 40 years ago.
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# Can Hat
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As a sub project to this board I have developed a little power and CAN distribution board combined with an MCP2515 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.
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With some more thought put into it I think it will be a good complement to the Huvud tool board.
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