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I've been trying to install an inductive sensor for auto-bed levelling into my Anet A8 and I'm having a few issues.

I have been using the wiring diagram provided by Solid Ground Electronics in one of his videos (

The sensor seems to work when I power the printer on, the red LED is constantly on and when it comes into contact with metal, the LED turns brighter (as shown in the photos).

However, when I set it to auto-home, the Z axis does not move down like it usually does (until it hits the switch), but it moves up a bit. Although when I auto-homed the printer with a piece of metal under the sensor, the Z axis moved down, like it should do. So the sensor is acting in an opposite way to what it needs to.

I believe that it's been wired up correctly with a 10k ohm resistor connected to the base of the transistor and the signal wire of the probe. However the NPN transistor shown in the diagram is '2N4401' and the one I used is 'PN2222A', but I believe this should have no difference in the function of the transistor (only the voltages it can handle).

I initially thought that as the NPN transistor is slightly different, perhaps the polarity of emitter and collector is incorrect, so I switched them around but the problem still occurs.

I would thoroughly appreciate it if anyone can help!

I've been trying to install an inductive sensor for auto-bed levelling into my Anet A8 and I'm having a few issues.

I have been using the wiring diagram provided by Solid Ground Electronics in one of his videos (Cheap 3D Printer - Anet A8: Upgrades, Experience & Thoughts), which I decided to follow as it still uses the Z limit switch, in case the inductive sensor fails to work.

The sensor seems to work when I power the printer on, the red LED is constantly on and when it comes into contact with metal, the LED turns brighter (as shown in the photos).

However, when I set it to auto-home, the Z axis does not move down like it usually does (until it hits the switch), but it moves up a bit. Although when I auto-homed the printer with a piece of metal under the sensor, the Z axis moved down, like it should do. So the sensor is acting in an opposite way to what it needs to.

I believe that it's been wired up correctly with a 10k ohm resistor connected to the base of the transistor and the signal wire of the probe. However the NPN transistor shown in the diagram is '2N4401' and the one I used is 'PN2222A', but I believe this should have no difference in the function of the transistor (only the voltages it can handle).

I initially thought that as the NPN transistor is slightly different, perhaps the polarity of emitter and collector is incorrect, so I switched them around but the problem still occurs.

I would thoroughly appreciate it if anyone can help!