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Simple and small battery gauge circuit?

rhd

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Does anyone have a simple circuit for scaling a battery voltage into progressive LED bars? Is it possible to do this with passive components? (I know there are ICs out there).

I'm looking to scale the voltage between 3.0 and 4.2 into between 0 and 20 LED bars.

Any creative solutions?
 





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A couple of LM3914 perhaps. Google bar display drivers. Just be aware remaining cell capacity is not linearly correlated with voltage.
 

Hiemal

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Somethin' like this should work

batt3914.gif
 

rhd

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I may turn to that, and in fact I already have a circuit designed around that chip, and pcbs, around here somewhere. It's just such a large IC. Even the SMD package is 10x10 mm.
 
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Might want to try something like this then, with op amps since you can get op amps in pretty small packages.

Except that's basically what the lm3914 is:

200971341723454.gif


I don't think 20+ op-amps and the added support circuitry is going to be smaller than 2 LM3914 :undecided:
 
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Beyond buying an Atml and writing code I'm not sure if theres an analog way to achieve what you are referring to. What is your intended dimension?
 
Last edited:

Benm

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The LM3914 solution is easy to implement, but only gives you and indication of battery voltage under test conditions. Open-circuit this will mean very little, though it may be meaningful when displayed under nominal load.

You could achieve the same function using something like an atmel or pic uC with analog inputs and lower cost and footprint though.

Using a microcontroller you can do a fair bit more though: add an external transistor and resistor to create a switchable load giving you voltage readings free floating and loaded at will. This will give you effectively a gauge of internal battery resistance, which is much more meaningful when gauging the charge status of nicd, nimh or lithium batteries.
 
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Attiny85, ill see if i can add some sample code when i get to my computer.

Actually maybe even the attiny10, that things tiny!
 

Benm

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The question becomes more a matter of the smallest package size you can solder if you take this route really. From a footprint perspective a TQFP complete atmel 328 (arduino) is already smaller than a DIP packaged LM3914. You could also go with any pic that has analog inputs and about 12 total pins so you can connect all the leds in a matrix.
 




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