Default Off-Pins while booting

  • Another laser-related question:

    I hooked up the TTL input of my laser control board to HEATER_3 and can use it without problems with [c]M452 P3 I1[/c] since 1.21RC4.
    While booting / initializing, the DuetWifi seems to toggle /set/reset all the pins and mosfets, which causes a few things:

    • my LEDs connected to E1 briefly flash on

    • all fans spin up briefly before the fan control gets set in config

    (if I had to guess, I would assume also E0 and the bed heater briefly turn on)

    This behaviour causes my laser to fire at full power for a split second, before the config.g is loaded and all pins are set correctly.

    Now the question:
    Are there any pins I can control with M452 that DO NOT show this kind of behaviour?
    I.e., I'm looking for a pin that is pulled low (?) the entire time, from power-on, through the booting, and through the config.g reading.

    I don't want to use some kind of R-C filter debounce magic, because this would also interfere normal operation (raster mode).

  • administrators

    The heater pins on the expansion bus are intended to be active low, because when the processor starts up they are pulled high by internal pullup resistors. That is why you need to use I1. We recommend that if you use them to drive a heater, laser or other critical device, you invert the logic signal (and level-shift it to 5V if necessary) before using it to drive your device. This guarantees that if for example the SD card cannot be read, the laser, heater or whatever will be off.

    Fans 0 and 2 will not spin up unless you have commands in config.g that control them. Fan 1 is deliberately on by default, because it is intended to be used for cooling the hot end heatsink.

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