comparator in the circuit that can be set to activate the LED on desired voltage.
The circuit can be adjusted to use with variety of rechargeable batteries from 6V to 24V. The LEDs can be adjusted according to battery voltage, for adjusting the circuit for a desired battery; an adjustable power supply will be required. For example you want to use the circuit to monitor a 12V battery then set 12.5V in the adjustable power supply and slightly adjust the variable resistor VR1 until the LED one goes off. After this set the adjustable power supply to 12.3V and slightly adjust VR2 until the LED2 goes off. Now set the power supply to 12.1 and adjust the VR3 until the LED3 goes off. At last set power supply on 11.9V and adjust the VR4 until the LED4 goes off. After these adjustments check all the settings once again by increasing the power supply to 12.6V and slightly down it till 11.9V and see all LEDs are going off on the adjusted voltage. If any LED is not going off on the desired voltage then adjust its variable resistor again. After all adjustments and testing are completed use some glue to stick the variable resistors.
A simple low cost and accurate 4 LED battery voltage monitor can be made using two lm358 operational ICs. Each LM358 IC contains two independent operational amplifiers, and the circuit is built using both amplifiers of each IC. Each operational amplifier is wired as a voltage
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