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I am wanting an at a glance indicator of what voltage level is being supplied by a DC generator (think pedal power). My general thought is a series of LEDs that light up in sequence as the input level increases, but I am having trouble coming up with a workable circuit. My voltage level can range from 0-24VDC, and I am looking for something that will indicate the current level in ~3V increments. The generator is the only power source I have, so comparators that need an external reference voltage or power source are out. I don’t need precise switching on the LEDs, they can gradually get brighter, but I would like something that only allows one at a time to be “partially” lit. I think I remember building such a circuit in one of my early electronics classes, but it has been many years, and the details elude me.

So basically the goal is 8 LEDs:
0-3V - LED 1 goes from off to fully on
3-6V - LED 1 is on, LED 2 goes from off to fully on
6-9V - LED 1 & 2 are on, LED 3 goes from off to fully on
etc.

I am thinking this should be possible with a zener/resistor/LED network, but every layout I have toyed with would push too much current through the lower level branches as I move up towards max power. So far my google skills are failing me in terms of finding a workable solution.

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Try the LM3914. It runs from a supply as low as 3V and drives up to 10 LEDs. The display is linear with input voltage too. Max supply voltage is 15V so some form of low drop-out regulator is required to limit it from seeing the full 24V.

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  • \$\begingroup\$ I am having trouble seeing how I would set up the reference voltages on this in a way that lets me power it from the signal voltage. It seems like it would need an outside reference point in order to function correctly. \$\endgroup\$
    – Rozwel
    May 17, 2015 at 18:26
  • \$\begingroup\$ Maybe you need to explain what trouble you are having. \$\endgroup\$
    – Andy aka
    May 17, 2015 at 18:41
  • \$\begingroup\$ Take a look at figure 19 and state your concerns maybe? \$\endgroup\$
    – Andy aka
    May 17, 2015 at 18:50
  • \$\begingroup\$ I have one DC generator that I am trying to get an output indicator on. That means I have a signal voltage that somehow has to become V+, Vhi, and Vsig on this chip, but still tell me where I am in the overall range. There is no battery or other supply that can be used as a reference. \$\endgroup\$
    – Rozwel
    May 17, 2015 at 18:52
  • \$\begingroup\$ The device has an internal reference that can be set to be about 1.25 volts. As for the input, you scale it down with a potential divider to make the appropriate number of LEDs work across the range of voltages you need. \$\endgroup\$
    – Andy aka
    May 17, 2015 at 18:54

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