3.7v Lithium Battery Level Indicator (Full & Low)

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In this DIY, we are developing the project of a “3.7V lithium Battery Level Indicator”. A battery level indicator is a device that provides “information about a battery”. There are two main components in making battery level indicators which are transistor BC548 and diode 1N4007.

The transistor BC548 is a general-purpose NPN bipolar junction transistor and a diode 1N4007 is a PN junction rectifier diode. These kinds of diodes permit only the flow of electrical current in one direction only.

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Hardware Components

The following components are required to make 3.7v Battery Level Indicator Circuit

S.no	Components	Value	Qty
1.	Transistor	BC548	1
2.	Diode	1N4007	1
3.	Multimeter	–	1
4.	LEDs	–	2
5.	Resistor	1K, 220Ω	2, 1

BC548 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of BC548

Circuit Construction

Step# 01

Connect 1k resistor in between the base and emitter of transistor BC548.

Step# 02

Connect the 220Ω resistor to the collector of the transistor BC548.

Step# 03

Then connect the 1K resistor with the 220Ω resistor.

Step# 04

Take diode 1N4007 and connect the cathode of the diode to the base of transistor BC548 and 1K resistor.

Step# 05

Connect the red LED in between the collector of the transistor and cathode of the diode and the green LED in between the end of the 1K resistor and the anode of the diode. Note that the positive of both LEDs should be with the collector.

Step# 06

Take red and black wires and connect the red wire with the positive terminal of the green LED and connect the black wire to the emitter of the transistor.

Step# 07

This is the complete circuit.

Step# 08

If we connect a fully charged Li-ion battery, the circuit will glow with a green LED.

Step# 09

If we connect a fully discharged Li-ion battery, the circuit will glow with a red LED.

Working Explanation

In this portion, we are discussing the circuit operation of the “3.7V Lithium battery level indicator”. This circuit requires some low-cost components like transistors, diodes, resistors, and LEDs. The battery level indicator is used to indicate the lithium-ion battery. When the Lithium-Ion battery is fully charged, the circuit will glow green light and when the Lithium-Ion battery is fully discharged, the circuit will glow red light.