We found this circuit in December 1986, Radio Electronics magazine. It uses 3 inverters and has the frequency determined by the crystal. The power supply is 5 V.
In this circuit of 1987 the player has to briefly press one of the keys trying to hit which LED...
This circuit was found in Radio Electronics magazine from February 1962. The sensor is an LDR, and the...
This 1970 Philips circuit uses a mechanical counter. The circuit is triggered by a reed switch...