This circuit is from March 1978 Radio Electronics. The 4-digit circuit uses a period module and is battery powered. The main integrated circuits are CMOS and TLL.
Found in a 90s Popular Electronics, this circuit uses two PLL tone recognizers to trigger by touch an...
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
This circuit is from 1995 documentation. In the original, the source is symmetrical at 12 V, but...