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IndustryArena Forum > WoodWorking Machines > DIY CNC Router Table Machines > CNC Router Parts > Proximity Sensors with MX4660 and Mach3, want some troubleshooting help
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  1. #1
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    Proximity Sensors with MX4660 and Mach3, want some troubleshooting help

    Hi everyone,

    I ordered a chinese proximity sensor from amazon the other day to try and get some homing switches set up on my 4x2 CNCRP machine. This one in particular: Amazon.com: Twidec /M18 Approach Sensor Inductive Proximity Switch PNP NO DC 6-36V, 8mm Detecting Distance LJ18A3-8-Z/BY: Industrial & Scientific

    I went with PNP NO sensors, I saw someone else on here had success using the same setup I'm using. I got the sensor in last night and hooked it up without an issue. The detection was working and I was able to confirm that it was working in the Data Monitoring ESS page, the checkmark on pin 10 would go on and off according to the sensor detection. When I jogged the machine and put the switch next to metal, it stopped the machine and I got the "limit switch activated" message.

    Today I cut a bracket to mount the sensor, and after I mounted it, it stopped working. I went in to look at my ports/pins configuration and afterwards, as usual, it said "ReConfigure EStop" and when I clicked the Reset button, I immediately got the "Limit Switch Activated" message. When I look at the Data Monitoring page, pin 10 has a continuous checkmark regardless of the sensor detecting metal.

    So, my question: is there something I'm missing in Mach3 or did my sensor go bad and short out? Based on the messages I'm getting from Mach3 and the Data Monitoring page, I'm thinking the sensor is shorting out. Which is concerning since I have 2 more coming tomorrow. I'll compare those two to this one tomorrow.

    I checked my wiring at the MX4660 and it was clean, but I also checked continuity and was getting continuity between the signal wire and the 12vdc wire on the sensor, even when nothing was being detected. But, these sensors are new to me so I wanted to check with you guys and make sure I'm on the right track.

  2. #2
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    Re: Proximity Sensors with MX4660 and Mach3, want some troubleshooting help

    Those Chinese sensors are pretty reliable. They don't usually go bad unless you do something to kill them (like shorting the output).

    Does the red LED on the sensor light up when you put a piece of metal near it?

    Are you measuring "continuity" with the sensor powered up and connected to the breakout board? That would not give you any meaningful results because there are voltages present in the circuit.

  3. #3
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    Re: Proximity Sensors with MX4660 and Mach3, want some troubleshooting help

    Interesting...I did test for continuity between the wires will connected and powered on. I assumed it just worked like a switch, but it seems that's not the case. These things are pretty foreign to me. Oddly enough, Mach3 started recognizing the sensor again for a few minutes last night before giving me the same problem as before.

    The red LED on the sensor does light up when I put a piece of metal near it. It doesn't trigger anything in Mach3 though. (Well, it used to...)

    I did a lot of digging yesterday, only to find I should have ordered NPN sensors instead of PNP. I also found that I can "psuedo" convert the PNP sensor to NPN with a pulldown resistor between the output and ground. Something about an open collector/floating pin/no path for current/etc. I honestly don't really know what the pulldown resistor does, but I figure it's worth a try. One thread said 680ohm based on a 12vdc input voltage.

    In the meantime, I'll remove the sensor and check for continuity, as well as resistance between the wires. I also read that there should be an internal resistor between the black and blue wires, might as well check while I'm in there with the multimeter.



    I know CNCRP sells sensors that are NPN NO. For some reason I thought they were PNP, but oh well. If I need to send these back and get some NPN it's not a big deal, I think it would be cool if I could make the PNP work consistently though.

  4. #4
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    Re: Proximity Sensors with MX4660 and Mach3, want some troubleshooting help

    I wondered why you bought PNP sensors. Most CNC board inputs are designed to work with NPN open collector devices. Also, it is customary to use NC for limit switches and stop buttons - so the equipment would stop if the switch wiring breaks.

    It is easy enough to convert a PNP switch to an NPN switch. One transistor (a good old 2N2222) and two resistors would do the trick. Sorry, I'm too drunk at the moment to calculate the resistor values. :cheers:


  5. #5
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    Re: Proximity Sensors with MX4660 and Mach3, want some troubleshooting help

    Quote Originally Posted by canman77 View Post
    I also found that I can "psuedo" convert the PNP sensor to NPN with a pulldown resistor between the output and ground. Something about an open collector/floating pin/no path for current/etc. I honestly don't really know what the pulldown resistor does, but I figure it's worth a try. One thread said 680ohm based on a 12vdc input voltage.
    The pulldown resistor activates the input - just like a closed switch would. The PNP switch, when triggered, "fights" that resistor and pulls the input up. This is not really a good technique, although it does work in some situations.

    In the meantime, I'll remove the sensor and check for continuity, as well as resistance between the wires. I also read that there should be an internal resistor between the black and blue wires, might as well check while I'm in there with the multimeter.
    As I understand, there should be no internal resistor, just the bare collector lead not connected to anything. This is why it's called "open collector".

  6. #6
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    Re: Proximity Sensors with MX4660 and Mach3, want some troubleshooting help

    I have a bunch of transistors lying around, I don't know if any are 2N2222...mostly 2N5088/5089. (I used to build a lot of guitar pedals)

    It's worth trying just for fun, but I think it'll be best to just order some NPN sensors!

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