Most of the circuitry is contained in the LM3914 dot/bar-graph driver IC chip. In addition to the comparator circuitry within the package, it also contains a stable reference supply and the drivers for the LEDs. Resistor R2 acts as the current limiter for all the LEDs. Resistor R2 may be varied for LED brightness. The unit will illuminate one LED for each voltage condition encountered in the charging system.
This system is called a dot-graph display; it is achieved by wiring the mode control at pin 9 to pin 11 on Ul. It is possible to wire the monitor so that each lamp will be illuminated up to the maximum voltage on the line at that moment. The latter is referred to as a bar-graph display. By connecting pin 9 to pin 3 on Ul, the bar-graph mode will be enabled.