This circuit is better than the previous one in that the control is isolated by a transformer. The transformer has 110 or 220 V primary and 6.3 to 12 V secondary with 200 to 500 mA current.
This circuit was found in a 1968 documentation. It makes use of both NO and NC reed-switches and small...
Found in a 90s American documentation, this circuit that was used in cars of the time, detects low...
This configuration was found in a publication for radio amateurs in 1975. It is a signal strength...