This simple continuity tester, whose configuration can be found several times on this site, is powered by only 2 batteries providing the indication on an LED.
We have many versions of biofeedback with the 555 IC on this site. This is another one. We found it...
This instrumentation amplifier with differential inputs was found in documentation from the 90s....
Found in an old Popular Electronics, this circuit warns when a remote lighting system is not...