This circuit was found in a documentation for radio amateurs from the year 70. Its purpose is to produce a tone on a transducer when transmitting messages in SSB telegraphy.
The two previous circuits show the INA185 a current sensing amplifier in basic applications. This...
This metronome configuration with the 555, quite common was found in a 90s Hands On Electronics. The...
This bidirectional circuit was found in an American documentation from the 80's. The LEDs are...