Need help with a schematic

[HatsVapes]

Im not super adept within the electronics world, though Im pretty damn good at soldering everything together lol. Im trying to make a very small battery life indicator but need help with a schematic.

basically there is a switch that turns the unit on and off and then to USE the unit when the switch is on you press the button. I want to put a very small LED battery life indicator on here.. basically a button and 5 small LEDs to indicate: 10%(RED), 25% (white), 50% (white), , 75% (white) 100% (green)

basically..
() () () () () [button]

I have an idea of the theory how this should work... button runs to the battery and then to the series of LEDs... any help drawing up the schematic would be awesome thanks!!

 

[carbonzit]

Unfortunately, what you want to do is a non-trivial exercise. You're going to need a circuit with some kind of voltage reference in it, to compare to the battery voltage, plus a comparator. You can't just string a series of LEDs together and have them indicate battery "life" (meaning voltage level) like that.

Are you using a 9-volt battery?

 

[alec_t]

Is the battery an alkaline one, a NICd, or what? They all have different discharge characteristics, so there may not be a 'one size fits all' solution.

 

[HatsVapes]

sorry I guess it would help if I provided the voltage used.

I have 2x 3.7v rechargeable Li-ion batteries

 

[carbonzit]

I have 2x 3.7v rechargeable Li-ion batteries

In series (7.4V) or parallel? I'm guessing in series, but it's better not to ASS-U-ME.

 

[HatsVapes]

basically the 2 batteries go through a circuit I already have and the output is 5v

 

[KJ6EAD]

You could just use an LM3914. It's made to do sort of what you want.

https://www.transkommunikation.ch/dateien/schaltungen/diverse_schaltungen/miscellaneous_circuits/Using%20the%20LM3914-6%20LED%20Bargraph%20Drivers.pdf
https://www.electro-tech-online.com/custompdfs/2011/09/LM3914.pdf
https://www.jameco.com/webapp/wcs/s...d=10001&freeText=lm3914&search_type=jamecoall

Often a bar graph LED is used for this kind of project.

https://www.kingbrightusa.com/categ...tegory_name=KCBar+Graph+Array&Page=1&orderby=

I like the three color models for battery voltage level indicators.

https://www.electro-tech-online.com/custompdfs/2011/09/DC3G4Y3EWA.pdf

 

[alec_t]

As was pointed out, this is non-trvial. LiIon batteries have a fairly flat discharge curve, so it's not easy to tell how much 'life' is still in them just by looking at the battery voltage. So the LM3914 may not be an ideal solution. One possibility is to use a microcontroller to monitor current draw and do the sums, but perhaps that's a bit OTT.

 

[KJ6EAD]

As was pointed out, this is non-trvial. LiIon batteries have a fairly flat discharge curve, so it's not easy to tell how much 'life' is still in them just by looking at the battery voltage. So the LM3914 may not be an ideal solution. One possibility is to use a microcontroller to monitor current draw and do the sums, but perhaps that's a bit OTT.

True, that's why there are a lot of Li-Ion battery fuel gauge chips on the market.

Here's an EEVblog video tutorial of a Li-Ion battery gauge design implementation using the LM3914.
https://www.youtube.com/watch?v=iIKGvHjDQHs&feature=player_embedded