This circuit makes use of a specific 80's component and was found in an American manual of the time. A matrix keyboard allows you to select one of several music programs.
We found this circuit that uses a thermistor as a sensor from the 1991 Electronics Experimenter Handbook....
Found in an RF Design from the 90's this circuit is intended for crystals of less than 1 MHz....
This circuit was obtained from an English circuit manual. Components are common and LEDs can be 3...