Found in a 90’s Electronics Now, this circuit has its output connected to an audio amplifier. The transducer is the type that fits on the finger to monitor the transparency and thus the beats.
We found this circuit in a 1967 Electronics World. The circuit can be designed to control other...
The presented circuit monitors a line indicating if it is busy if there is an extension. The...
This circuit is from old documentation. The operational amplifier is uncommon nowadays. The...