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.
Throw a micro at it is often a good option these days. If the circuit it would be replacing was any more complex, I'd gladly trade off some software development effort for reduced hardware assembly effort. But in this case the circuit is so conceptually simple - a comparator and an oscillator - that I'd be more tempted to go in the other direction and just use discrete transistors. Like most of my projects, it is being pursued to address a practical need, and not just for the fun of it, so I'm optimizing for least effort at a reasonable cost. (My first pass was to look at off-the-shelf automotive battery monitors. But I didn't find any that behaved the way I want.) I can probably prototype the circuit (comparator or op-amp version) on a solderless breadboard in under an hour, and build the final version on some perf board in another hour. Any micro option would require a bunch of overhead time to get up to speed, plus programming hardware in some cases, so not the best trade off. > First thing is I'd probably talk to your architect and see just how > important that blinky pattern really is. :-) I have a specific use case in mind where it will be useful. I need an indication that can easily be observed at some distance (20 ft), and is easy to distinguish the states, gives an active indication when things are working, and a more attention getting indication when the low battery condition occurs. > http://www.atmel.com/dyn/resources/prod_documents/2535S.pdf > http://www.instructables.com/id/Tiny-AVR-Microcontroller-Runs-on--a-Fruit-Battery/?ALLSTEPS I've ran across this (or at least other AVR-family) micro before and have some bookmarks set on it: http://www.avrfreaks.net/ http://shop.tuxgraphics.org/ (lots of kits that have Ethernet, including a host watchdog: http://tuxgraphics.org/electronics/201102/eth-network-watchdog.shtml) Feature-wise, it seems to be like a successor to the PIC. > you might even be able to PWM the LED so it looks like its on all the time > through persistance of vision, but actually saves some battery juice. Yup. A micro would also permit making the blink rate proportional to voltage. Both of those could be fairly easily done with a VCO, but by that point the micro circuit would start showing an advantage in simplified hardware. But neither of these are requirements for my application. > Or, get a bi-color LED... I'd be more apt to take the lazy approach and use a pair of LEDs - a green one wired to one comparator to light when the voltage is good, and a blinking red LED wired to another comparator (used as a buffer/inverter) that illuminates when the voltage is below threshold. Or if I wanted to pay $14 for an LED I could get a programmable "smart" LED: http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2123645_-1 that could do slow fades across the RGB spectrum when OK, and rapidly blink red when in low battery state. :-) (I think the only control mechanism it offers is I2C, so if you need a micro to switch from OK to bat low states, then it isn't very practical.) > Just a thought. Thanks for the ideas. -Tom _______________________________________________ Hardwarehacking mailing list [email protected] http://lists.blu.org/mailman/listinfo/hardwarehacking
