Getting bed probing piezo sensor to work

  • Hi Duet forums,

    I have a piezo sensor for bed leveling, it consists of 3 piezo discs, some electronics and firmware (
    It works with RUMBA electronics (5V) and some smoothie based electronics (3.3V).
    I have a trouble connecting it to my Duet 0.85 (1.15e firmware),
    I tried 2 ways:

    1. Connected to probe input: I't would work ok, but because it's designed as NO the value drops when the sensor is pressed, so the probe readings are 1000 idle and drops to around 600 when pressed. For the firmware of course it's constantly pressed. I tried rising and falling edge and different thresholds too. It would be ok only it's inverted.

    2. Connected to E0 or E1 stop. The problem with this sensor is it gives around 1.9 - 2.2 V (measured with standard meter not oscilloscope) when pressed so the LOW value is desperately high for 3.3V and thus does not trigger logic. I tested the setup with RRD Hall sensors which work like a charm.

    Is it possible to get it to work somehow? I have limited way to fiddle with the sensor itself.

  • administrators

    If the probe reading only drops to 600 when the sensor is activated, then it sounds to me that it isn't compatible with a 3.3V supply. One possibility is to run it from 5V and feed the output through a couple of resistors to an NPN transistor which drives the E0 endstop input.

    I'll probably add a firmware option to invert the Z probe polarity for type 1, 2 and 5 Z probes at some point, then you will be able to connect it directly.

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