IC:U1 – LM3914
Resistors (All 1/4 watts)
R1 – 4.7K
R2 – 4.7K (preset to set upper limit)
R3 – 1.2K
R4 – 4.7K (preset to set lower limit – 10.5V)
The LM3914 acts as a LED driving voltmeter that has its basic maximum and minimum readings determined by the values of R1 and R2. When correctly adjusted, the unit actually covers the 2.5 volt to 3.6 volt range, but, it is made to read a supply voltage of 10 volts to 15 volts by interposting potential divider R1to R2 between the supply line and the pin-5 input terminal of the IC. In this circuit, the IC is configured to give a ‘dot’ display, in which only one of the 10 LEDs is illuminated at any given time. If the supply voltage goes below 10.5 volts none of the LEDs illuminate. If the supply voltage equals or exceeds 15 volt, LED 10 illuminates.