This circuit can be used to test up to three LEDs at once, connected in series. You can easily increase that number by using a higher supply voltage. If you do so, you should allow 2.7 V for each ...

3V is sufficient to turn on any LED, but is within its reverse break down voltage rating (that is why I did not use the common 9V battery). Short circuit current is approx. 30mA. I used a 3V lithium ...

A blast from the Elektor archives: this clever 1998 battery tester uses a simple LED display to reveal a battery’s true condition under load — even below 1 V. Built from standard components and no ...