We found this circuit in the October 1991 issue of Radio Electronics magazine. The circuit uses common components and can still be assembled easily today.
We find this microphone voice effect in 1992 documentation. The vibration of the relay contacts...
We can also use the 4011 on this CMOS circuit that makes use of a crystal headset. The power...
We found this circuit in documentation from the 1980s. The integrated circuit used is uncommon today,...