This sequential tone generator circuit was found in the July 1980 issue of Radio Electronics magazine. It uses well-known integrated circuits. The tones are generated by programming resistors.
We found this circuit in an American publication from 1977. The circuit drives two LEDs according to...
We found this circuit in a 1972 RCA technical documentation. The comparator can be any type and C1...
Similar circuits can be found on this site. This is from an 80's American documentation. The...