This circuit triggers an LED when the input signal exceeds the peak, or the value set in RV1. The transistors can be the modern equivalents BC549.
This circuit is from a 1979 publication. The sensor consists of plates or screens that, when...
Found in an 80's documentation this circuit uses an integrated from the uncommon era today. Other...
This circuit was found in a Popular Electronics from the 90s. It uses a LASCR which is a photo-SCR...