Emergency Battery Tester

Whenever we have the remote control’s pair of batteries down, we have no way to know whether they are or not. Most often time, it is seen that people bang the back of remote and press keys thereafter, when things work, people ignore the low battery and if they don’t we change the batteries. Since this is a luxurious requirement, the problem of low battery of the appliance for hearing impaired or pace-maker holding patients is critical. Here is a simple low battery indicator or tester circuit. The circuit can also be used as a basic demonstration of voltage divider circuit & use of NOT Gate

The circuit is built on a NOT Gate that will drive the LED as an indicator. Input to the NOT Gate is from a voltage divider circuit. The battery under test (BUT) creates the potential across the voltage divider circuit. The drop across one of the resistor is fed as input to the input of the NOT Gate. The entire circuit is powered with 5V DC Supply or +9V Battery.

Whenever the appliance is not working, simply power this circuit, place the terminal of the BUT at the input. If the voltage of the battery is less than 1.6V, the LED will glow, else it won’t.

(For testing purpose, I have used 2 (1.6V each) pencil cells. Together they create 3.2V. The input to the NOT Gate is 1.6V which is taken as HIGH and the LED does not glow. When one battery is removed, the total voltage now is 1.6V & voltage drop at the input of NOT Gate is 0.8V, which is taken as LOW and the LED glows.

The circuit should be soldered and fabricated in a suitable cabinet so that the BUT is placed at terminals and result is seen.

Here is the Video of the circuit built by me.