Least expensive low-battery indicator?

[Don French]

Anyone have any thoughts on the least expensive way to implement a low-battery indicator?  The restriction is that the indicator circuit should not consume any appreciable power itself.  So it could be a LED for example that blinks for a few ms every few seconds when the battery is low.  I was thinking of doing this with a small uC that wakes up every few minutes and reads the voltage on the battery and controls the LED.  But I wonder if that is the least expensive way to go and if so, which one people would recommend.  FWIW, the circuit is powered by a 3.7V 600 mAh battery.

-- Don

[Don French]

I came up with a solution on my own. My device already has a LED that I flash for a couple ms every 10 seconds to let the user know that the device is alive and well.  So it occurred to me that I can use that same LED to indicate low power by simply changing the flash rate if the battery is low.  The PIC10F220 seems ideally suited for the task.  It costs $0.34 a pop and has a ADC, can directly drive a LED, and has a watchdog timer that can be set to wake the sleeping processor at a regular interval.  At wakeup time I use the ADC to compare the battery voltage to the regulated 5V supply and set the flash rate accordingly. So I saved one LED and got everything I need for $0.34 and a very small footprint on the board.  Pretty slick, huh?

[Camp Peavy]

> Pretty slick, huh?

 

Very slick and resourceful!

 

- Camp

 

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[William Garrido]

I think this is a little old but this is what I use and thought someone could use it.

http://dsscircuits.com/lipo-fuel-gauge.html 

Works great. Only limitation is the i2c address can't be changed, but only matters if you want to use more than once. Then you can use soft i2c, which works. 

The owner if the site is great and pretty flexible. He is also the one that did a all in one tracker on kickstarter. 

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-William

http://mobilewill.us