3.7V Battery Low and Full Level Indicator Circuit




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Hii friend,

Today I am going to make a circuit of 3.7V Battery low and full charge indicator.

Let's get started,

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Step 1: Take All Components As Shown Below

Components required -

(1.) Transistor - BC547 x1

(2.) Resistor - 1K x2

(3.) Resistor - 220 ohm x3

(4.) pn-Junction Diode - 1N4007 x1

(5.) LED - 3V x2 (Red for Low charge indication and Green for Full charge indication)

(6.) Battery - 3.7V and 3V

Step 2: Connect 1k Resistor

Firstly we have to connect 1K resistor to Base and emmiter pin of the transistor as solder in the picture.

Step 3: Connect 220 Ohm Resistor

Next solder 220 ohm resistor to collector pin of the transistor as you can see in the picture.

Step 4: Connect 1K Resistor Again

Next we have to connect 1K resistor again.

Solder 1K resistor in series to 220 ohm resistor as solder in the picture.

Step 5: Connect 1N4007 Diode

Next connect 1N4007 Diode to the circuit.

Solder -ve of Diode to base pin of Transistor as picture.

Step 6: Connect Green LED

Next Solder +ve leg of green LED to 1K resistor which is connected to collector pin of transistor and

solder -ve pin of green LED to +ve of diode as you can see in the picture.

Step 7: Connect Red LED

Next Solder +ve leg of Red LED to Collector of transistor and

solder -ve leg of Red LED to -ve of diode as solder in the picture.

Step 8: Testing - 1

Now our circuit is completed and now we have to check this circuit.

Connect +ve of 3V battery to +ve leg of green LED and -ve of 3V battery to emmiter pin of the transistor as you can see in the picture.

~ As in abouve picture glowing Green LED Because this battery is fully charged.

Step 9: Testing - 2

When I connected 3V battery then Red LED is glowing and Green LED is also glowing in small amount.

~ Hence when Battery will be full charge i.e. 3.7V then Green LED will glow only and when battery will be low i.e. 1.5V then Red LED will glow only.

Thank you

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    7 Discussions


    Answer 7 days ago

    Moving the "plus" input on the other side of the 1k resistor, so between the 2 resistors (1k & 220), will change the voltage threshold. This circuit isn't reliable nor precise. Electronicians know diodes direct voltages aren't stable and that there's no zener effect even if it looks like.


    12 days ago

    You should protect the transistor's base with a resistor, actually it is directly connected via the green led (1.8V~) and the diode (0.6V) without any current protection. I need to test but I'm sure the transistor will get too hot.


    Question 4 weeks ago

    How to modify 6'9'12 volt circuit?


    4 weeks ago

    would really love explanation of what happen too, and a way to test other batterie (1.5V, 9.0V, etc...)


    5 weeks ago

    Thanks for that .Its interesting . Do you understand what is happening in the circuit and can you explain that to me?