I have a keypad I would like to interface to another application. I am having a hard time getting any kind of diagram on it so I took apart one of the switches. Each switch has a tiny magnet that passes through a coil, yet no reed switch. It receives 24Vdc and I am wondering how the circuitry is set up to detect the switches. Has anyone ever worked with one of these Cortron keypads before? thanks
That would be a tiny EMF generator.
Should be some op amps somewhere.
Magnet switching can be done with a reed switch (but that's expensive), or a Hall sensor, but it can also be done with a saturating transformer core: the magnet saturates the core and decouples two windings from each other. I've seen a toroid with two staples (one turn windings) with a magnet on the key plunger implementing such a switch.
It's possible to use a linear generator, setting a flip/flop on (+) pulses and resetting it on (-) pulses, but this is unreliable unless a nonlinear element (like a Wiegand wire) is part of the magnetic circuit.
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