This circuit produces a 300 Hz signal from a 10V input. The circuit is from a 60's documentation, making use of components from the time.
The circuit shown is suggested by National Semiconductor's Linear Applications Handbook. The base...
This circuit uses a pickup coil to take the signal from a telephone line without contacts. The circuit...
In this circuit, the transistors are NPN for general use and the phototransistors can be replaced by...