This simple bridge circuit can be used for impedance or resistance measurement using a high impedance earphone as an indicator. The circuit is from an American 80's documentation.
We found this circuit in an old publication. The ICM7556 is a dual CMOS 555. The other components are...
The operational used is uncommon today, but equivalents can be used. Unlike the previous one, this...
This musical doorbell was found in a Popular Electronics from the 90s. The U4 melody generator...