Telephone ringing circuits
Copyright Tomi Engdahl 1997,2000,2005
Preface
Telephone circuit gain always interrest, because telephones are everywhere and quite often there are old telephone luying around somewhere. Those telephones can be used for many interresting experiments including small home intercom: connect telephones in series or parallel and feed suitable operating current (about 20 mA) to them through resistor from power supply.