The integrated circuits used in this project are uncommon today. It is worth the idea for a microcontrolled project or with equivalents. We found this configuration in an old documentation.
This circuit uses a crystal phone and can be built with more modern transistors like the BC548. The...
The resistors in this circuit marked with * must be within 1% tolerance. The circuit is from the...
The existence of field effect transistors at the input of the integrated circuit (operational...