LED Battery Level Indicator

[Kc7fys] came up with a this simple battery level indicator. It uses a single LED to display a battery’s voltage; if the voltage exceeds 12V, it glows green. If it is below 11V, the LED glows red. Anything in between generates an orange glow. The meter is built around an LM358 chip per this schematic, but his actual build looks pretty sloppy because of the dead-bug assembly (check out NASA’s pretty version). Nonetheless, it works, so clean it up and build one if you want to put it (or your batteries) to the test.

16 thoughts on “LED Battery Level Indicator

  1. Quick, dirty, and effective, nice to see a real hack from juan.

    With the addition of a 555, you could probably rig a version that blinks an led with increased frequency as the battery voltage approaches the threshold of operation.

  2. Juan, each time i see one of your posts i want to kill someone, do you know who im talking about? Yeah, i think you know ;)´

    Can you stop killing HackaDay.com? Really, this is going very very down each day thanks to you.

    Saludos desde Argentina.

  3. @drix
    would people stopping bitching about posts on here?
    is it your web site?
    your getting this listing for free based on what they think people might like to read.
    i for one enjoy all the extra posts.

  4. @drix this is actually a decent post for once, and lay off the threats, it’s unneccecary.

    On the matter of the device, that 7805 regulator is really inefficient if all you need is a reference voltage. it should probably be replaced if you don’t want this thing to eat the battery it’s supposed to monitor.

  5. can someone compose an idiots guide on what all i need to build this? I cant read schematics well But i have a “project” this would be good for. (car battery and car CD player with a couple speakers mounted on the side of an ammo box for a portable off road radio.)

  6. @giskard: If you look at the schematic, the 7805 isn’t actually powering anything. It’s connected directly to the op-amps. The datasheet claims a quiescent current of 5mA. While that’s certainly no micropower circuit, bear in mind the device is also continuously lighting one or two LEDs at what appears to be 12mA each. I wouldn’t even use the circuit on a car battery, since the standby current of a car is supposed to be under 20mA and the battery will still run down if you leave it too long. But it might be handy as a test probe you can use to check a lot of batteries for good/okay/bad charge levels.

  7. A uC implementation would require fewer components. You would only need: uC + 2 resistors (plus the leds and their resistors.)

    Most uC’s have an ADC and an internal precision voltage reference. Mixing the colors can be done with PWM.

  8. I saw a battery level indicator at the dollar store yesterday with 3 red leds. Maybe not as cool cause it doesn’t change color but I guarantee a heck of a lot cheaper at 1 buck.

  9. why even have a green “voltage OK” LED? I would make it simpler and just have a “voltage low” red LED, and get rid of the voltage regulator and 1 of the op amps.

  10. @Dark_AvEnGer: You’re right, this is not MY website, but i think that the original idea of ¿Eliot Phillip was the creator? was a blog were he can put interenting hacks to show to people. We are the people, so, if that is right, they do the blog for US (that its beacuse ITS A PUBLIC BLOG), and i think they have to care about us, otherwise they will loose us (and they ARE loosing us).

    @giskard: yeah, maybe its a decent post (well, a comparator with an op-amp it’s not a new idea, but well…), but not for hackaday. Hackaday its for hacks (or im wrong? someone tell me that i am, if i do), and you can’t tell me that this is a hack, ’cause it isn’t AT ALL.

    If Juan like to post something like this i really recommend him instructables.com, but i think hackaday it’s not the place for him.

    I’m a reader of hackaday from many years ago, and i can tell you that a few years ago, this type of posts was VERY strange to find here.

    saludos desde argentina

    PS: Sorry by my bad english, im from argentina and i do my best to talk in english.

  11. It’s funny how NASA has written down all those precise requirements and considerations for electronics, and yet the space shuttle has loose joints and tiles falling off and gasket that go brittle in a most predictable manner and cases where 2 out of 3 computers fail.
    Makes you wonder.

  12. ‘Pretty sloppy’? Oh, well, for a kit builder building one of his first off-the-kit-grid items from a schematic, this is not bad. Does it work? That is the real determiner. One word, ‘Yalp.’
    I used it recently on a field radio trip to Vietnam and it showed best when my power supply was being ‘pulled down’ on transmit by blinking from green to orange, or from orange to red. See the finished product–sloppy my ass!
    Jonathan, who build this voltage meter designed by Stephen Weber KD1JV

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