This circuit was found in Radio Electronics from the 90s. The sensor is an oscillator whose frequency depends on humidity, an uncommon component nowadays.
This circuit activates an output, which can be a lock, only when a card containing the programmed code...
This circuit was found in Popular Electronics from 1993. The 1458 consists of a double 555. The...
This is a Serial In - Parallel Out or Serial Out [SIPO or SISO] shift register using the...