Battery Level Indicator

Here is the circuit diagram of abattery level indicator.This circuit is very simple and very cheap and compact.It can be used in transistor one band,two band or three band.This circuit is also  used in emergency lights and other power supply circuits.

Battery levels,normal or are indicated by the green or red LED repectively.One can set the circuit for monitoring the level of the battery within 3 to 10V with the help of 10k preset.
Transistor T1 is 'ON' due to the voltage divider biasing.Green LED is 'ON' as the collector of T1 is almost at ground.

When voltgae drops below the preset voltage,T1 switches off as the voltage is not sufficient to bias it to "ON" state.But the voltage at the base of T2 is sufficient to switch on T2 to conduction. Thus red LED glows-indicating the under voltage state of the battery.

Circuit Diagram

                                                    Source : http://www.expertcircuits.blogspot.com/

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