Duet 2 Wifi - Need for a fourth fan that can be switched off

[MartinNYHC]

For my second Duet 2 Wifi controlled printer I need a fourth fan for a HEPA filter that can be switched off when not needed. Any ideas?

Thx!

[droftarts]

@martinnyhc Simplest way is to use a spare on-board heater channel, if you have one. All signalling on the expansion header is all 3.3V, and there's no fan headers; the DueX uses a I2C expander chip + mosfets to drive the additional fans, and a 74HCT02 chip + mosfets to drive the additional heater outputs.

I think you could use one of the expansion header heater pins to drive a MOSFET/relay/buck converter, with power for the fan coming from an external source.

Ian

[MartinNYHC]

@droftarts How can in control (switching on/off) an expansion header pin? Couldn't find anything in the docs. Or am I blind?

[droftarts]

@martinnyhc Are you using RRF2 or RRF3?

Generally, see https://duet3d.dozuki.com/Wiki/Using_servos_and_controlling_unused_IO_pins

In RRF3, create a fan with M950 F#, and set the pin (C parameter) as "exp.heater3" (for example), and any other options eg PWM frequency. This will give you control of the pin using M106 P# ...

In RRF2, you need to disable the default use of the heater pin with M307 H# A-1 C-1 D-1, then it should be useable by the M106 command, using the A parameter to set the logical pin number of heater3.

As the output of the expansion header pins is only 3.3V, you need additional circuitry to drive a switch (MOSFET/relay/buck converter) to provide 5/12/24V (or whatever voltage your fan is) to the fan.

Ian

[MartinNYHC]

@droftarts Perfect. Thanks!