Battery Warning Circuit

2camjohn said:

I need a low battery warning circuit that turns on an LED when two 9V batteries need replacing.

If anyone has a circuit like this or knows any websites which cover this kind of stuff please help.

I am limited for space so the smaller and simpler the better.

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2camjohn said:

Thanks again Nigel, it looks quite simple.

I am using two 9V cells which drive a motor at 15v, I want to provide a warning when the battery is beggining to die.

I see yours provides a warning once a 9V cell gives 6.5V, that seems a little low to me.

What voltage would you suggest to turn on the led as the battery is just starting to run out?
I would rather warn people too early than too late.

Also should I just wire the battery warning circuit to one cell or both?

As the whole battery will be replaced at once.

Thanks

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jpalomba said:

It seems it would be possible to use a opamp and a bargraph led to make it a more precise battery indicator correct? Also, I was under the impression that nine volts batteries held 9 volts of voltage until the very end where there was a dramatic voltage drop. It would seem that the circuit there measures a drop in voltage.

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