I have previously reported on a USB interface for a Honeywell Micro Switch keyboard (viewtopic.php?f=7&t=24122, I should update that with the finished project) and I complained about two dead keys. I managed to replace the Hall effect sensors in those with common 3-pins 3144 sensors and I thought that might deserve a separate post.
These are 4A3S switches. The sensor inside is 4-pins, with an active-low enable input the 3144 lacks. But some of the keys have the enable input hardwired to ground, making them always-on and these sensors I could replace (moving their original, working sensors to the faulty keys). This picture sums it up:
- Left: The 3144 sensor face up. Pins left to right are 5V, GND, output (open collector).
- Middle: Another 3144 face down and with pins bent to match the original plate in the keyswitch. The original sensor has been removed with a knife from the plate; the pinout left to right is 5V, output, enable, GND.
- Right: Finally, a "prepared" 3144 soldered to the plate and ready to go inside the keyswitch again. Again, this works because this sensor will go in a switch with grounded enable pin (3rd from left).