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
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.