Wiring Schematic Diagram

This is a volt meter circuit based on LM324 OpAmps chip. A bargraph generator is nothing more than a slack-handful of OpAmps, all thrown into a single chip. It is cheaper to use the LM324 and put in the few extra components needed.

R1 to R8 down the left all form a voltage divider from the 7.5v Zener diode. The resistors give me taps of 0.5v, 1.5v, 2.5v, 3.5v, 4,5v, 5.5v, and 6.5v. The top of the zener gives me the eighth voltage: 7.5v. These reference voltages are all connected to the negative-acting input of each OpAmp, and all the positive-acting inputs are gathered together for a common input. With 0v on the +ve inout, the output voltage of avery OpAmp is 0v.

If the input voltage lies between 0v and 0.5v then no LED lamps will light. If the input voltage rises to between 0.5v and 1.5v (1v +/-0.5v) then the first LED will light when the first OpAmp +ve input exceeds the -ve input threshold. In this way the LEDs all form a nice bar-graph display in 1v steps, +/- half a volt.

The A-B-C links should be in the A-B position for a normal bar-graph display, when each LED succesively lights as the voltage rises. With +4v input there will be four LEDs lit. If you fit the links in the A-C position then only one LED will light for each voltage step, to give a moving dot display. The top (last) link should always be in the A-B position for both modes.


This Op-Amp Voltmeter Circuit From www.sm0vpo.com:800