This QST circuit generates 4 frequency signals according to the crystals used. Transistors admit equivalents although the indicated types can still be found with some ease.
This circuit uses a photocell as sensor and a sensitive relay according the power supply voltage....
This 2005 circuit from a Linear Technology manual makes use of the LTC610HV and an optical coupler that...
The 4093 or any other NAND gate can be used for the very sensitive configuration of a R-S...