This circuit was found in the August 1972 issue of Radio Electronics magazine. The circuit generates 4 types of signals as can be seen in the diagram. The maximum frequency is around 20 kHz.
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...