CNC Axis Home detector using QRD1114 IR proximity sensor

by Stephen Hobley on July 6, 2010

One thing missing from our CNC routers is an automatic axis home circuit. This is something that signals the control software that the gantry is in a known position (usually at the origin). A lot of CNC hobbyists like to use the end mill as part of the homing circuit – this is OK, but does not take into account different sizes of bit diameter. A better solution is to have the X/Y home switches attached to the linear axis. Then the home position will be the same regardless of bit diameter.

Initially I wanted to use Hall Effect sensors, but the detectors themselves proved difficult to get. I’ve had some QRD1114 reflection sensors for some time, so I thought it was about time I put them to good use.

Initially I used a PNP transistor to amplify the switching signal from the sensor, but this proved to be way too analog. The resulting signals were not very clean. So instead I used an LM324 opamp configured as a comparator, with a simple potentiometer providing the reference voltage. A 1M resistor is used for feedback, providing some hysteresis around the switching point. Eliminating any potential chatter that can occur.

Once we have the system fitted and working – I’ll be publishing a howto guide.

This switch will be used to home the X and Y axes, the Z axis will be using a touch plate.


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