The tone generated by this bell changes when we press and release the switch. The circuit is from a 1985 Radio Electronics. Some changes can be made to improve its performance.
In this circuit the photo-transistor signal is amplified by a Darlington step and then applied to a...
The purpose of this circuit of an American publication from the 70s is to move the signal from an...
This 80's circuit can be implemented with modern equivalent FETs with lower on resistance. The...