This project contains the hardware schematics and design choices for a low cost printer control board for RepRap hardware. Current boards are very capable, but make decisions on cost and feature set that are not of my choice. By making this available, I aim to add another option out there.
Making the printer control a drop in selection, this will permit re-use of existing driver breakouts (e.g. Pololu A4988's and DRV8825's) and with SPI support for TMC2300 breakouts, it allows an upgrade path. and low cost upgrade potential for existing printer controllers.
!! Warning - this is still work in progress !!
This board is based around the ARM MCU STM32F412RGT running at 96MHz in a LQFP-64 package. There are a few free pins, and with some ingenuity, some pins can be multiplexed/multi use.
Future intent is to port MarlinFW to this package, from the PlatformIO platform. Programmers for these devices are relatively cheap, but there remains the possibility of a 0 cost programming option via the USB DFU device capabilties.
Selling these individually is not possible in todays marketplace without some additional testing and regulation, but those requirements need to be investigated and addressed as development progresses.
As the majority of components are surface mount (SMD) with only a few through-hole components, the plan is to complete the bill of materials (BOM) for the SMD components and send for professional fabrication on the prototypes.
Initial CircuitMCU SelectionPower SuppliesPCB LayoutRaspberryPi interface(Abandoned due to lack of space for an interface)5V Power Output (on 2.54mm pitch 2x2 connector)- Review
- Feedback
- Component Selection (BOM)
- Fabrication
- Testing
- Firmware Development
- Added 3.3v and I2C to the breakout port for possible expansion
- Shifted E0/E1 Filament sensor feedback to make room for I2C port
- Adjusted some routes for the 2x4 breakout port
- Added totem pole drivers for the heater MOSFET's - switching time is <1uS so it should be possible to drive at 1MHz frequency if ever needed
- Altered heater LED indicators to Red
- Validated Fan PWM MOSFET's - 4mA is enough to drive at around 4uS which is plenty fast enough and won't overload GPIO pins
- Altered layout to accomodate new components
- Split MCU controlled components into their own sheet - not enough space on a single sheet for everything!
- Abandoned the idea of putting in a Pi Interface - difficult to maintain a 2 layer design and route everything for the 2x20pin GPIO interface of the Pi
- Added ZVD Ideal diode for 5V output
- Exposed 5V output (after ZVD) for external consumption (e.g. powering a Pi)
- Added a copper pour on the top layer for an Earth plane
- Re-Routed a few signals to maximise covered area on pour
- Upped trace size for power lines to 0.8mm
- Initial Commit