This circuit was found in a Popular Electronics from the 90s. The counter circuit is not common today. The circuit can be programmed for hourly intervals, according to the values of R4 and C2.
Found in a documentation from the 90s, this circuit has a typical accuracy of 2% with 20 V signals at...
Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime...
This low drift circuit for thermocouple was found in an old European documentation. However, it is...