This circuit was found in an 80's Poptronics. The circuit is a fast trigger whose signal can be taken from the Q2 collector. The supply can be done with voltages from 9 to 12 V.
This circuit with LDR and neon lamp has its operating frequency given by the light. The circuit is from...
Found in American documentation from the 90s, this circuit can be used as a shield with the...
This tone recognizer circuit that relies on R5 and C1 was found in the December 1994 issue of...