This 1974 circuit uses two 555 integrated circuits in a very traditional configuration. The circuit can be powered by voltages from 9 to 12 V and for greater volume an amplifier stage can be added.
This two-tone decoder has a bandwidth of 24%. The circuit is from a 1994 Electronics Now. The...
This circuit was found in a Popular Electronics of the 1980s. The microammeter may be the lowest...
This sensitive circuit can be designed with FETs such as BF245 and MPF102. The sensor is a silicon...