Magnetic reed switch as a non contact sensor

I have found a cheap magnetic sensor (switch) that can be used to sense change in movement. Easily mounted the switch has two small slots that will match upto standard half inch spacing. The slots will have to be opened up slightly if you plan to use Meccano bolts to mount though, which is easily done with a 4.1mm drill bit.
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The switches are available in the UK from RS Compnents and the part no is 331-743. Price is a just over £4 UK each.


I have found that the small magnet that came with the Meta Cruiser kit that Meccano marketed in the late nineties works well with the switch and will trigger the switch at upto 8mm. Mounted into a bush wheel the magnet can make an excellent positioning device, with improved accuracy for more magnets being used equally spaced in the bush wheel. Email me at if you would like a picture of the sensor with a suggested mount and actuator.