This circuit was found in a 1968 documentation. It makes use of both NO and NC reed-switches and small magnets attached to a card in the form that results in the drive combination.
This circuit was found in a Motorola documentation from the 70s. The integrated circuit is from...
This circuit is from 1990 documentation. It uses a bridge with LEDs and the potentiometer must be...
The values of R and C are set so that a time constant of the same order of magnitude as the...