This circuit converts a high voltage into a frequency using an optical coupler. The transistor can be 2N2646 and the coupler admits equivalent. The circuit is from a 1974 publication.
This extremely slow circuit produces one pulse per month and can be used in a timer. We found it...
This circuit was found in a 1964 Electronic Design. The circuit delays the firing of a load for a...
Found in a documentation from the 90's, this circuit already includes an amplification stage. The...