We found this circuit in a documentation for radio amateurs from the 70s. The transistors can be the BC548. With it, small speakers of 4 or 8 ohms can be used as microphones.
Using the HA2400 this circuit has its output voltage digitally programmed from the references...
Assembled with SMD components this circuit can be very small. The range is a few tens of meters. We...
This circuit can be used as a shield when its supply is 5 V. in this case we can exchange the...