This circuit was found in a 90s Popular Electronics. It uses an LS3404 melody chip that has several recorded melodies and that is uncommon nowadays.
This amplifier for hearing aid was found in a 1968 documentation using an integrated of the time....
We obtained this circuit from a 1993 documentation. The circuit has 9 current ranges that are...
In the figure we have the transmitter of a data transmission system with optical fiber suggested by...