We found this circuit in documentation from the 90s. Instead of a voltmeter, you can use the voltage scale of a multimeter. The circuit tests batteries under load.
We can use the circuit shown below, obtained from a 1992 documentation. To turn a low impedance phone...
High-brightness LEDs of various colors and even white can be obtained easily in specialized...
This circuit is from an American publication about old neon lamps. The circuit is leak proof and...