<html><head><style type="text/css">body {word-wrap: break-word; background-color:#ffffff;}</style></head><body><div style="font-family: sans-serif; font-size: 16px">ah, well, I got the impression that minimum number of parts was the chief requirement, and I probably added minimum current as number two.<br><br>if time and effort is high on the list then all the overhead of a microcontroller isnt justified.<br><br><font face="sans-serif"><span style="font-size: 14px"><i><font color="#333333">Connected by DROID on Verizon Wireless</font></i></span></font></div><br><br>-----Original message-----<br><blockquote style="; border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><div style="font-family: sans-serif; font-size: 14px"><b>From: </b>Tom Metro <tmetro+hhacking@gmail.com><b><br>To: </b>hardwarehacking@blu.org<b><br>Sent: </b>Sat, Mar 31, 2012 19:36:37 GMT+00:00<b><br>Subject: </b>Re: [HH] low battery indicator<br><br></div>Greg London wrote:<br>> If you want something that specific, and as few parts as possible,<br>> you might be better off trying something like a tiny microcontroller.<br><br>Throw a micro at it is often a good option these days. If the circuit it<br>would be replacing was any more complex, I'd gladly trade off some<br>software development effort for reduced hardware assembly effort.<br><br>But in this case the circuit is so conceptually simple - a comparator<br>and an oscillator - that I'd be more tempted to go in the other<br>direction and just use discrete transistors.<br><br>Like most of my projects, it is being pursued to address a practical<br>need, and not just for the fun of it, so I'm optimizing for least effort<br>at a reasonable cost. (My first pass was to look at off-the-shelf<br>automotive battery monitors. But I didn't find any that behaved the way<br>I want.)<br><br>I can probably prototype the circuit (comparator or op-amp version) on a<br>solderless breadboard in under an hour, and build the final version on<br>some perf board in another hour. Any micro option would require a bunch<br>of overhead time to get up to speed, plus programming hardware in some<br>cases, so not the best trade off.<br><br><br>> First thing is I'd probably talk to your architect and see just how<br>> important that blinky pattern really is.<br><br>:-) I have a specific use case in mind where it will be useful. I need<br>an indication that can easily be observed at some distance (20 ft), and<br>is easy to distinguish the states, gives an active indication when<br>things are working, and a more attention getting indication when the low<br>battery condition occurs.<br><br><br>> <a href="http://www.atmel.com/dyn/resources/prod_documents/2535S.pdf">http://www.atmel.com/dyn/resources/prod_documents/2535S.pdf</a><br>> <a href="http://www.instructables.com/id/Tiny-AVR-Microcontroller-Runs-on--a-Fruit-Battery/?ALLSTEPS">http://www.instructables.com/id/Tiny-AVR-Microcontroller-Runs-on--a-Fruit-Battery/?ALLSTEPS</a><br><br>I've ran across this (or at least other AVR-family) micro before and<br>have some bookmarks set on it:<br><br><a href="http://www.avrfreaks.net">http://www.avrfreaks.net</a>/<br><a href="http://shop.tuxgraphics.org">http://shop.tuxgraphics.org</a>/ (lots of kits that have Ethernet, including<br>a host watchdog:<br><a href="http://tuxgraphics.org/electronics/201102/eth-network-watchdog.shtml">http://tuxgraphics.org/electronics/201102/eth-network-watchdog.shtml</a>)<br><br>Feature-wise, it seems to be like a successor to the PIC.<br><br><br>> you might even be able to PWM the LED so it looks like its on all the time<br>> through persistance of vision, but actually saves some battery juice.<br><br>Yup. A micro would also permit making the blink rate proportional to<br>voltage.<br><br>Both of those could be fairly easily done with a VCO, but by that point<br>the micro circuit would start showing an advantage in simplified hardware.<br><br>But neither of these are requirements for my application.<br><br><br>> Or, get a bi-color LED...<br><br>I'd be more apt to take the lazy approach and use a pair of LEDs - a<br>green one wired to one comparator to light when the voltage is good, and<br>a blinking red LED wired to another comparator (used as a<br>buffer/inverter) that illuminates when the voltage is below threshold.<br><br>Or if I wanted to pay $14 for an LED I could get a programmable "smart" LED:<br><a href="http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2123645_-1">http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2123645_-1</a><br><br>that could do slow fades across the RGB spectrum when OK, and rapidly<br>blink red when in low battery state. :-)<br><br>(I think the only control mechanism it offers is I2C, so if you need a<br>micro to switch from OK to bat low states, then it isn't very practical.)<br><br><br>> Just a thought.<br><br>Thanks for the ideas.<br><br> -Tom<br>_______________________________________________<br>Hardwarehacking mailing list<br>Hardwarehacking@blu.org<br><a href="http://lists.blu.org/mailman/listinfo/hardwarehacking">http://lists.blu.org/mailman/listinfo/hardwarehacking</a><br></blockquote></body></html>