Using 4 operational amplifiers this circuit generates 4 different tones. The circuit is from an American documentation from the 90's. Operational amplifiers are tTL084.
We found this circuit in an English publication from the 1980s. The circuit uses current...
The circuit shown in the figure can be useful in cases where a common telephone extension is used....
We found this circuit in an American documentation from 1977. The circuit must not be powered by a...