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 a 1968 Electronics World. The transistors are from the era and...
In the figure we have the way to implement a monostable with an operational amplifier LM393. The...
Suggested by Motorola documentation from the 1980s, this circuit makes use of MOSFETs of the time....