We would like to suggest a circuit, which we think will be especially appreciated by those being involved in DIY electronic accessories for motorcycles and cars. The specific circuit is a voltage indicator, which displays the status of the battery connected to its positive terminal. Since most cars are not equipped with such an accessory, it could be quite useful. The 12V battery level indicator consists from only one LM3914 integrated circuit (see IC1) and 10 LEDs, connected on IC's outputs.
The LM3914 is a monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs, providing a linear analog display. It contains its own adjustable reference and accurate 10-step voltage divider.
In the proposed circuit, the resistors values have been calculated to ensure that the last LED (LD10) will light up when the voltage reaches approximately 14.5 volts. LD1 will turned off, when battery's voltage drops below 10 volts. In principle, for each LED diode that will be turned off, there will be a 0.5 volts (in practice only 0.45 volts) reduction in voltage.
If you wish to change the values of the reference minimum and maximum, you can simply act on the values of R6 and R4. Reducing the value of R6, will lower the value of the minimum. In contrary, increasing the value of R4 will raise the maximum.
The circuit was initially designed to operate in bar-graph mode. However, LM3914 also supports dot-mode. To operate in dot-mode, just leave the Mode Select pin (pin 9) open circuit. Operating on dot-mode has the advantage of lower current consumption. That is because every LED consumes about 15mA and, when operating in dot-mode, only one LED will be turned on, at any possible voltage value.
List of components
D1=1N4007 or equivalent
R4=680 ohm, 1/4W
R5=18K , 1/4W