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.
This receiver for listening to headphones and 2-battery power was found in Japanese documentation from the...
This circuit was found in a Texas Instruments optoelectronics manual and can work with any...
This circuit activates a relay when raindrops fall on the sensor. The circuit is from 1960...