Electrical & Audio Guides
LED bargraph voltmeter
Not a particularly complicated circuit, only using basic components and an IC to display the voltage level of the battery on a LED bargraph.
The circuit uses an LM3914 bargraph driver to do all the complicated bits of converting the voltage signal to an output for the bargraph. The input for the IC is derived from the power supply to the circuit, unlike some circuits where they need a separate power supply to compare the input to. The limits to the range of the display are set using R13 and R14 and the display mode can be switched between dot and bar mode using a jumper on the links LK1.
to set up the circuit after construction, connect it to a variable power supply and use R13 and R14 to set the limits, this is done as follows. Set the input voltage to 11 volts and adjust R14 until the first red LED just lights, then set the input voltage to 15 volts and adjust R13 until the last red LED just goes out. This process may need to be repeated several times until the first and last LED's light at the specified voltages.
Diagrams:
Diagram for the main circuit
Stripboard layout for making the circuit
