This circuit was found in a 1980s US publication. It indicates when the phone is off-hook by triggering an indicator.
This 48 V circuit with a capacity of up to 105 V was found in a 2005 Linear Technology manual. The...
This circuit prevents damage by accidentally reversing the power supply polarity. The circuit is...
It can be obtained from Mouser Electronics new tactile keys subminiature SMT KMR 6 Series C & K....