The Duet 3 Mainboard is a next generation controller board that builds on Duet3D's experience in developing the most flexible 3d printer control solutions. It is the core of the Duet 3 family which provides control for a wide range of machines including 3d printers, CNCs, lasercutters and more. The overall aim with the Duet 3 series is to allow for maximum flexibility of machine design through highly capable main boards, expansion boards, smart tool boards and custom expansion modules. The flexibility of configuration and advanced features are enabled by our innovative RepRapFirmware 3 running on the Mainboard and DuetSoftwareFramework running on the single board computer.

Initial documentation is available at: Duet 3 Setup Guide with full documentation under development now.

The Duet 3 Mainboard 6HC is the first version of the main board produced.

The main hardware features of the Duet 3 Mainboard 6HC are listed below.

• Compatible RepRapFirmware versions: RRF 3.x

For firmware update instructions when running in stand-alone mode, see Installing and Updating Firmware. If running from an SBC, see Getting Started With Duet 3

click on the image for a larger version

On Duet 3 the mounting holes are isolated and not plated through, they have a keep out area around the M4 clearance hole of an additional 2.2mm radius. Any metallic mounting solution should keep inside this keep-out area.

Please note:

• If you mount the board on a metal surface, use standoffs to ensure that the back of the board cannot short against the plate. A minimum standoff length of 5mm is advised, however larger is preferred for better cooling.
• Do not use metal washers under the mounting screws, or screws with large heads (e.g. button head). Nylon washers are recommended and supplied with the board. With a metal washer or large screw head there is a risk of creating a short.

TO DO

The STEP file for the Duet 3 Mainboard 6HC is shared on the Duet3D github here:

https://github.com/Duet3D/Duet3-Mainboar...

For wiring, see Duet 3 Mainboard 6HC Wiring Diagram

For a description of the connections provided, see the Duet 3 Mainboard 6HC Wiring Diagram

For pin names in RepRapFirmware, see Duet 3 Mainboard 6HC Wiring Diagram

For a description of the LEDs on the board, see Duet 3 Mainboard 6HC Wiring Diagram

There are 9 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. IO output pins can be used as inputs, but are only 3.3V tolerant.

On the version 0.6 and 1.0 boards the individual IO_x connectors have the following additional capabilities:

On the Duet 3 prototype v0.5 main boards the capabilities are different:

VIN in the range 12V-32V must be provided to the Duet. In addition the same, or a different voltage can be provided specifically for the very high current OUT0 circuit. This allows for a heated bed or similar to be run from an alternative power supply. If that is not required the same VIN can be supplied to the OUT0 input.

The Duet 3 produces 12V onboard from VIN. 12V will not be produced if only 12V is provided as VIN. 12V is provided to the low current (800ma) fan voltage selection pins, and can be assigned to two banks of pins, OUT 4-6 and/or OUT 7-9.

The Duet 3 also produces onboard 5V and 3.3V, from VIN. These voltages are divided for internal and external use, with external 3.3V and 5V going to IO and other headers.

Previous versions of the Duet 3 Mainboard 6HC allowed for the Duet to power the SBC, or the SBC to power the Duet. More modern SBCs (e.g. RPi 4) needs too much 5V power, especially with a screen, to make it sensible to supply from the Duet. Similarly the spare 5V power budget on the SBC may not be sufficient for the Duet. In addition some SBCs require >5V on the 5V rail to not give an under voltage warning.

Due to this, the jumpers for 5V power between the Duet and SBC ('5V -> SBC' and 'SBC -> 5V*') are not populated on this board revision.

5V produced by the internal regulator can also provide power to a connected SBC (Single Board Computer, eg Raspberry Pi), via protection that normally prevents the SBC from backfeeding the Duet. There is an array of jumpers to customise the 5V power setup as required:

The default configuration has jumpers on the "Int 5V EN" (Internal 5V enable) and "5V -> SBC" pins only. This means the internal 5V is enabled and the SBC is powered by the Duet's 5V. The Duet can supply up to 3.0A to the SBC.

Alternatively, the SBC can provide 5V for the Duet using the "SBC -> 5V" jumper. Note that the Duet's in-built protection is bypassed. In this case the "5V->SBC" and the "SBC->5V*" jumpers should both be fitted, but remove the jumper from "Int 5V EN".

If you wish to power the Duet and SBC separately, fit just one jumper, to "Int 5V EN". The Duet will be powered by it's internal 5V regulator and the SBC from it's own 5V power supply.

Please note no other jumper configuration is recommended or supported.

Powering a SBC like the Pi3 from the Duet is feasible provided any USB peripherals attached to the Pi are very low power draw or have their own separate power supply. Higher power draw SBC like the Pi4 may draw more power than the internal 5v on the Duet can supply, especially with added peripherals. In general, for best results, it is recommended to power the Duet and the SBC separately to avoid power overdraw issues.

Furthermore, it is recommended to use a sufficient power supply for the Pi4 that is capable of providing 5a. The official Raspberry Pi Power Supply is a good example of this. Additionally, the USB cable used to power the Pi must be of good quality.

Power overdraw conditions may result in poor communication between the Pi and Duet. The Pi may display a lightning bolt icon on the display (if connected) which is a good indication there is a power supply problem.

The Duet 3 mainboard has a dedicated high speed SPI bus to a single board computer (SBC). The reference implementation is a Raspberry Pi 3B or newer. The SBC provides the user interface (via a browser based control application called Duet Web Control, or a third party application). It also provides a network interface via the local network or VPN depending on how it is configured. It runs a set of applications called DuetSoftwareFramework(DSF) that use the SPI bus to communicate with the Duet, as well as providing a webserver for DuetWebControl, and API for third party application, and a plugin interface specifically for gcode processing plugins.

Documentation for DSF to follow

The Duet 3 can also be run in standalone mode (without the SBC) in the same way as Duet 2 by using the on-board SD card socket and Ethernet interface, but then the advanced facilities of DSF are not available.

The Duet 3 has 6 TMC 5160 stepper drivers on board. Until further testing including detailed thermal analysis is conducted these are limited to 4A RMS. The initial testing of the TMC5160s in this configuration, conducted on the Expansion board looks very promising. 4A per phase will allow driving stepper motors rated to up to 5A RMS (it is recommended to drive stepper motors at around 80% of rated maximum current).

RepRapFirmware configures these drivers over the SPI bus: dynamic setting of microstepping, current and many other features can be achieved through firmware. The drivers can be combined together to use multiple drivers on one axis (for example a 3 motor Z levelling system).

Endstops of a variety of types can be connected to any of the 9 IO headers and mapped to a specific axis. One or more Z probes can be connected (for example a different Z probe per tool). In addition filament monitors for extruder drives are supported. 9 headers allows for an endstop on 3 motion axis, 3 z probes and 3 filament monitors on 3 extruder axis - or any other combination.

To do: document the additional functions such as PWM/analog/UART etc available on the IO headers

The Duet 3 has 10 PWM controlled outputs. These can be configured as heaters, fans or other devices that need a PWM signal (such as spindles or pumps). There are capable of different current outputs:

Note: maximum total output from the on-board 12V regulator is 1A.

See CAN connection

The CAN-FD bus provides connectivity to compatible devices. Duet3D will be manufacturing a range of expansion devices, starting with a 3 channel expansion board The maximum number of expansion devices on the bus is to be determined: however we expect at least an additional 24 stepper channels via 8 x 3 channel expansion modules will be supported.

The CAN BUS is connected via RJ11 and at least 2 core twisted pair, although 6 core RJ11 is more common.

The Ethernet port provides the ability to directly network to the board - along with the built in SD card this provides a reduced feature set (similar to Duet 2) method of controlling the Duet 3.

The Ethernet port may also provide potential to support EtherCat in the future if this is implemented.