This simple electronic music box circuit was found in the April 1985 issue of Radio Electronics. The components are common, and the note adjustments are made with trimpots.
We find this circuit in an American 80's documentation. It makes use of IC sensor which is mounted...
This is a configuration obtained from an old manual, using an operational amplifier of the time....
In the figure we have the way to add hysteresis to an operational amplifier. The relationship...