6-30v capacitive sensor

  • Hi,
    I use a capacitive sensor and I have some issue wiring it to the duet.

    On the ramps I was using the Z end stop switch to use it. it was using a voltage divider bringing it to 3.24 v (two 7.5k resistors in and 1 10k to bring down the signal line voltage from 12v to 3.24v.)

    On the duet, I tried to connect it on the E0 end stop using M558 P4 and state change aren't detected and I trigger the sensor and check it with m119

    I suspect that it's caused by the led problem that is draining power from the signal line or something like that

    I tried to connect it on the Z_PROB_IN pin using M558 P1. The state change are detected by M119 but it doesn't stop the Z axis. I suspect that since this connector is usually used by an analog sensor my sensor isn't managed correctly by the firmware

    David, in another post you talked about the possibility to implement a new p5 switch on the m558 command to manage that kind of sensor as digital input on the prob connector. Do you know when you will have the time to do that ? I don'T want to rush you but since this input doesn't have led It think it would fix my issue with the setup that I had on my previous board making the switch easier

    Having siad that, for now is that someone could give me some hints on how I could get that sensor working ? It's a show stopper on the duet setup right now.


    sorry for my english. It's not my main language 🙂

  • administrators

    The new P5 probe type is already implemented in the 1.14 firmware release.

  • @dc42:

    The new P5 probe type is already implemented in the 1.14 firmware release.

    oh nice.

    I just tried it but it still doesn't works 😞

    M558 P5 X0 Y0 Z1 S0 (s0 since the sensor is open by default)

    If I do m119 I get 'at min stop' when the sensor isn't triggered and 'stopped' when triggered but doesn't stop Z motion

    any hint ?


  • administrators

    S0 doesn't work on M558 at present, so a type 5 Z probe needs to have an active high output.

    Is your sensor PNP or NPN output?

  • David,
    The bad type I guess. so in the moment I don't have the choice to use the E0 stop pins . Any input how I can that working with what I've right now ? I cannot get E0 stop triggered at all. I think it's a voltage/led issue. I even tried to feed the pin with 4.02 volt and the led wasn't bright as the other end stop leds

  • administrators

    I can't help unless you tell me what sort of output it has.

  • David,
    it's a normally open sensor so the logic must be inverted, it looks like that:http://www.aliexpress.com/item/LJC12A3-H-Z-BX-DC-6-36V-1-5mm-Distance-Capacitive-Proximity-Sensor-Switch/1726079980.html

    it's connected on 12v and I was lowering the output voltage using some resistors to bring it at 3.24v to use it on Z endstop pin on the ramps


  • administrators

    According to http://www.mikrocontroller.net/attachment/279364/Condutive_Proximity_Switch_Series.pdf the /BX ones are NPN output and the /BY are PNP output. So if it is a /BX type then instead of resistors, you should use a small signal Schottky diode, connected cathode to sensor output and anode to the STP pin on the E0 endstop connector. A silicon diode such as 1N4148 may work as well, but although that seems to work for some people, the last person I suggested it to found that it pulled the E0 STP pin low enough to light the LED on the Duet at less than full brightness, but not low enough for the Duet to recognise it as triggered.

  • Thanks David, it works perfectly with the 1N4148 diode. I was able to got that one at a local store near here.

  • administrators

    I'm glad it worked for you. I'm in the process of completing the documentation pages at https://duet3d.com/wiki/Duet_Wifi_Wiki. I've done the page on endstops, I'm currently doing the page on thermistors, and I'll eventually do the page on Z probes.

  • administrators

    I have now documented how to connect several different sorts of Z probe at https://duet3d.com/wiki/Connecting_a_Z_probe.

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