The Duet 3 Expansion board 3HC v1.0 3 channel version supports the following:

• 3 high-current stepper drivers
• 3 high current PWM-capable outputs (provisionally 5A each maximum)
• 3 medium current PWM-capable outputs (provisionally 3A each maximum), 2-pin
• 3 outputs for 4-wire fans (separate PWM control wire and tacho)
• 9 low voltage input/output connectors. Some of these have additional facilities, for example UART capability.

Connectivity to the Duet 3 Mainboard is over the CAN-FD Bus.

Firmware limitations: See Duet 3 firmware configuration limitations.

click on the image for a larger version

DC42 conducted thermal tests on the drivers running at 4.45A RMS (6.3A Peak) per phase:

First image: Test setup.
Second image: FLIR image after 10 minutes, with no fan cooling, and the reported MCU temperature was 62.4C.
Third image: Adding a quiet 40x20mm Sunon fan brings the temperatures down nicely; the reported MCU temperature came down to 43C. Ambient temperature during these tests was 27C.

3HC STEP File on github

The wiring diagram is here: Duet 3 Expansion 3HC Wiring Diagram

For a description of the connections provided, see the Duet 3 Expansion 3HC Wiring Diagram

For a description of the LEDs on the board, see Duet 3 Expansion 3HC Wiring Diagram

For pin names used by RepRapFirmware, see Duet 3 Expansion 3HC Wiring Diagram

There are 6 IO headers on board. Each has an input and output along with 3.3V, 5V and Gnd supplied. This enables them to support a wide range of endstops, probes, filament monitors and future low bandwidth devices.

RepRapFirmware 3 can be configured to map these ports to the appropriate functions as required.

Except as noted in the table below, an IO_x_IN pin can always be used to provide a digital input (e.g. for endstop inputs or filament monitors), and an IO_x_OUT pin can always be used to provide a digital output. On the version 0.6 and 1.0 boards the individual IO_x connectors have the following additional capabilities:

VIN in the range 12V-32V must be provided to the Duet expansion board. The board produces onboard 12V, 5V and 3.3V, from VIN (12V will not be produced if only 12V is provided as VIN).

These voltages are divided for internal and external use. with external 3.3V and 5V going to IO and other headers, and external 12V if provided to the low current fan voltage selection pins.

Max 12V current: The two banks of Low Current outputs (OUT3-5, OUT6-8) can be separately selected to be powered by either VIN or internal 12V. Total 12V fan current draw must not exceed 800mA.

Max 5V and 3.3V current: Up to 800mA from 3.3V and 5V combined, of which no more than 500mA from 3.3V.

See also CAN connection

Two RJ11 connectors labeled CAN IN and CAN OUT. In fact it doesn't matter which you use for the cable from the main board and which you use for the cable to the next expansion board, because they are wired in parallel.

The DIAG LED between the two CAN connectors indicates CAN bus state. When the expansion board starts up this LED will blink rapidly. If the expansion board is connected to a main board running compatible firmware, the LED on the expansion board will switch to blinking synchronously with the main board LED once time sync has been established across the CAN bus.

Just behind the RJ11 connectors is a 4-pin terminal block. On the last board in the CAN chain only (the one with a cable in only one of the RJ11 connectors), two jumpers must be fitted in that block to terminate the CAN bus. Jumpers must not be fitted in expansion boards that are not at the end of the CAN bus.

The Duet 3 Expansion 3HC has a 4-bank DIP switch to set the address. The CAN address is set by the switches as follows: