'Fuel Gauge' battery meter

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piesoup

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Morning all
I have seen that the Tiger Lights come with a fancy array of little LEDs on the back of the light that register the capacity of the battery. You know, 5 lights, that reduce as the battery runs out.
Does anyone know of a circuit that i can make to get the same effect.
I'm running 4x XR-E off 12v NiMh through a MaxFlex 3.
I have searched for it but with no luck!
Thanks all
Andrew
 
Piesoup, I made exactly what you are talking about - even the same amount of cells -12NiMH. It is absolute so you need no other voltage input refrence and you can adjust it to what ever voltage you like.

I have just run out to my garage and can only find my veroboard layout diagram but not the circuit diagram so I don't even have the values!!! If you give me a few days i'll put up a picture of the potted assembly (measures about 3x3x0.8cm) and will also try and find the circuit diagram.

At the time it was the only circuit in the whole web I could find that didn't need an external reefrence voltage AND was adjustable to suit your voltage. Also it has a trimmer pot to get the segments to lihjt up exactly as you want.

Marco.
 
marcopolo said:
Piesoup, I made exactly what you are talking about - even the same amount of cells -12NiMH.
[...]
At the time it was the only circuit in the whole web I could find that didn't need an external reefrence voltage AND was adjustable to suit your voltage. Also it has a trimmer pot to get the segments to lihjt up exactly as you want.
Click to expand...

If you dig up the diagram, definitely post it.
 
marcopolo said:
Piesoup, I made exactly what you are talking about - even the same amount of cells -12NiMH. It is absolute so you need no other voltage input refrence and you can adjust it to what ever voltage you like.

I have just run out to my garage and can only find my veroboard layout diagram but not the circuit diagram so I don't even have the values!!! If you give me a few days i'll put up a picture of the potted assembly (measures about 3x3x0.8cm) and will also try and find the circuit diagram.

At the time it was the only circuit in the whole web I could find that didn't need an external reefrence voltage AND was adjustable to suit your voltage. Also it has a trimmer pot to get the segments to lihjt up exactly as you want.

Marco.
Click to expand...

Mate, that sounds perfect! Nice and small by the looks of it too. I have trawled the web too and couldnt find a thing, use all the online search engines and nothing! It'd be smashing if you could dig out a diag and a pic.
Ta very muchly
Andrew
 
15 google searches and 1 hour later I was still scrathcing my head trying to figure out where I got the circuit/article.......then bingo....I remembered a friend who was building a 12v based wind turbine set-up had an old journal: "home Power" from 1989 (april/may)

I dug the article out and googled "bat-o-meter" and yippee found it in some obscure homepower archive 4 pages:

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/10/10pg27.txt

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/10/10pg27a.gif

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/10/10pg27b.gif ....... the pot of gold!!

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/10/10pg27c.gif ..........24v version

What amazed me at the time was that it is way more simple than any other circuit using the LM 3914.

It works great and you adjust the voltage you are measuring by changing the zener voltage value which sets the baseline. I think I just used a 12v zener instead of an 11v zener (which gives a low voltage warning of around 1v per cell) but you could get a 13v zener for a roughly 1.1v low voltage warning per cell. The trimmer sets the LED brightness.

enjoy.

Marco.
 
One more thing - the 5v regulator they use (7805) from cicra 1989 - could easily be replaced with a much smaller regulator, maybe even as small as 100mA as long as your LED brightness is low - mine is as I wanted miniumum battery drain.

So you could use a 0.1A fixed posivide 5v regulator such as this:
http://www.maplin.co.uk/Module.aspx?ModuleNo=46470

Also to help miniturisation, once you know what LED brightness you want you could replace R3&R4(pot) with a single resitor.
 
marcopolo said:
15 google searches and 1 hour later I was still scrathcing my head trying to figure out where I got the circuit/article.......then bingo....I remembered a friend who was building a 12v based wind turbine set-up had an old journal: "home Power" from 1989 (april/may)

I dug the article out and googled "bat-o-meter" and yippee found it in some obscure homepower archive 4 pages:

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/10/10pg27.txt

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/10/10pg27a.gif

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/10/10pg27b.gif ....... the pot of gold!!

http://www.ibiblio.org/ecolandtech/alternative-energy/homepower-magazine/archives/10/10pg27c.gif ..........24v version

What amazed me at the time was that it is way more simple than any other circuit using the LM 3914.

It works great and you adjust the voltage you are measuring by changing the zener voltage value which sets the baseline. I think I just used a 12v zener instead of an 11v zener (which gives a low voltage warning of around 1v per cell) but you could get a 13v zener for a roughly 1.1v low voltage warning per cell. The trimmer sets the LED brightness.

enjoy.

Marco.
Click to expand...


I really appreciate you finding the info for me. Thanks very much!
I have ordered some bits online, I'll test it out and replace the pot with a fixed resistor. Also fancy using a 555 timer so when the mom switch is used to change modes etc on my MaxFlex the lights come on for a short time. Hope to get some pics up when its made!
:thanks:
 
That's a nice looking setup, Sabrewolf. :cool:

The LED digital displays I linked are more for those that are concerned about keeping track of Li-Ion balanced cell voltages, and actual numerical ranges. They work at lower NiMH voltage levels also. They wouldn't fit in most Maglite setups like yours do.
 
I made something like this (sorry for the bad quality, I just took it with my cell phone!):
0301092343a.jpg



It was made using a LM324 Quad op-amp. It is set up as a comparator. You you wanted, I could give the the schematic. It's pretty simple to set up. I made it adjustable using the little pot at the top. Each LED has about 0.7V difference between lighting up. I have another one that uses 4 LEDs..no additional parts besides the LED.

Right now its set up as

GREEN: ~12.6V
Yellow: ~11.9V
RED: ~11.0V

You can adjust the pot and make it something like >8.0V green, >7.2V yellow, and <7.2V red. That was a good setup for my 6cell NiCd.

Here's a link to where I got the Idea: http://www.uoguelph.ca/~antoon/gadgets/batt324.htm

I modified to different voltages though.
 
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