[HH] low battery indicator

[Tom Metro]

Greg London wrote:
> If you want something that specific, and as few parts as possible,
> you might be better off trying something like a tiny microcontroller.
> 
> It's the chip, a cap on the power pin, a resistor and LED.
> 
> Maybe wake up once a second to check the voltage, use the ADC and the
> internal reference to figure out the external voltage. Then either pulse
> the LED on then off, or leave it on, then sleep for another second or so.
> 
> You'd need a low current voltage regulator and two resistors to divide the
> battery voltage down to something the ADC could sample. But it would be
> programmable, so you could blink any pattern you want.
> 
> ...get a bi-color LED, and hook it up between two output pins fo teh
> chip. Then you can PWM it green for good power, adn pwm it red for low
> battery.

Looks like someone beat us to this:

http://www.vellemanusa.com/products/view/?id=525836

It's a 12V battery monitor made from a single 8-pin chip, regulator,
bi-color LED, and a few discretes.

"...add this LED monitor so you know the condition of your car's
battery. Indicates a good battery (green, solid), blinks while it's
charging (green, slow blink), show low voltage (red, solid), and shows
overcharging (red, fast blink)."

Not quite the pattern I wanted. And I don't care about indicating
charging or over charging. They also get fancy with the LED blinking by
fading it on/off.

A video showing it working:
http://www.youtube.com/watch?v=0JEo1_XCJJ4

Sold here:
http://www.smarthome.com/76517/Velleman-MK189-12V-Battery-Monitor-Kit/p.aspx

as a kit for $7 or assembled for $10.

The sales literature is pretty useless as far as telling you what is in
the circuit. Clearly its a micro, but the photos:
http://cache3.smarthome.com/images/76517big.jpg
seem to have the part number blanked out.

However, the instruction manual reveals that IC is a "programmed PIC
10F220-I/P" and it confirmed that the TO-92 device is a 78L05 regulator.

They don't bother to include a schematic (only a hookup wiring diagram
for the finished product), which is pretty sad for a supposedly
educational kit. No mention of which resistors form the voltage divider
or how to adjust the thresholds, if even possible.

And of course no source code provided.

 -Tom