This circuit for frequencies of 20 to 2 kHz was obtained in English documentation from 1966. The transistor can be any general purpose and powered by batteries.
This circuit, also suggested by Texas Instruments, uses a photo diode in the reception and a field...
The output stage of this amplifier can operate at high voltage. The transistor must be a high...
We found this circuit in a 2002 documentation. It allows you to turn off the devices connected to a set of...