Found in a PE Hobbyst Handbook of 1991, this circuit was originally proposed to time photographic baths in developing rooms but can be used for other purposes. The circuit beeps at 30-second intervals.
Found in a Popular Electronics from the 90s, this game can be seen in other configurations on this site. The...
This interesting electronic Christmas tree circuit using LEDs and integrated CMOS was found in a...
We found this circuit in an American 80's documentation. The resistors must be of high precision...