Help Reading the Duet2 Wifi Schematic

  • I need some assistance reading the schematic for the Duet2 Wifi found here:

    I went ahead and have ordered some tool breakout boards based on this project:

    Having got excited and already got some boards I've now had a closer look and realised that these tool boards rely on the use of a common power rail with controlled components like the heater and fan being controlled on the negative. I've dug into the schematic but got myself confused, it's been a long time since I've had to delve into electronics and I'm not sure what's going on.
    For example the heater control:
    I really can't work out what's going on here and how this relates to how the heater is connected, if someone could point me in the right direction or even just knows whether this tool board will work or not, it'd be appreciated.

  • E0- represents the same E0- as shown on the wirng diagram. This is the "ground" for the heater, and it is switched by the mosfet (i.e. low side switching)
    The other pin on the wiring diagram is actually V_FUSED, and goes through the fuse F2 and to V_IN.

    E0_PWM is the 3.3v signal form the CPU.

  • @littlehobbyshop said in Help Reading the Duet2 Wifi Schematic:

    I am about 95% certain that board will work fine with a Duet. It appears to have common +12V for the fans and heater, and separate ground for each. Which is what you need. It should also work for 24V, assuming you use 24V fans and heaters.

  • Thanks both, I will carefully proceed. I'm using 24v everywhere so should be good.

  • EDIT: I've solved the problem below, the heater supply and drain were crossed, meaning I was PWM controlling the whole supply to the tool board rather than just the heater.

    So, an update. Everything is now connected. BL Touch is working, thermistor is working, extrusion motor is working. I am having a problem with the fans though.

    When the hotend heater comes on, the heatsink fan completely dies, as PWM starts to kick in as the heater reaches it's setpoint, the fan starts to ramp up again.
    Without the heater on, PWM behaves as expected on the fan.
    I have power to the tool board coming direct from the PSU, wiring is sufficient diameter, nothing feels like it's getting warm where it shouldn't.
    It appears to be a voltage drop issue where supplying the heater causes the fan voltage to just die. Connecting the fan drain to ground gives no improvement, the fan dies when the heater is supplied. I can't work out why though? It's a standard V6 heater at 35W (1.46A @24v) the wiring and connectors used should be good for 5A at least.
    As luck would have it one of my Fluke leads also died today so I can't even measure it reliably.
    Here's how I have it wired, 24v from PSU, drain from each the fans and heater go to the corresponding drain pins on the Duet mainboard.

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