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 _______________________________________________ Hardwarehacking mailing list [email protected] http://lists.blu.org/mailman/listinfo/hardwarehacking
