Well in theory it can be done with a single pic and mic... no two alarms are likely to exhibit the same period and frequency and amplitude. Sampling all these using a DSpic and a few leds could indicate the culprit reasonably simply.. Job for an explorer 16 and a microphone... Just my 2p.. steve -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of Dr Skip Sent: 30 November 2009 20:19 To: Microcontroller discussion list - Public. Subject: Re: [EE] Making a Smoke Alarm distinctive 99tweet Time spent chasing this AND any complex design will end up totaling more than the lifetime time spent replacing the batteries... ;) A cross between simple, cheap, time-effective and having a little engineering involved would be your idea of a mic on each, run to an amp with enough gain to clip the signal, then use it to trigger something like an LED in the house, a 555 to an LED for longer duration or a largish cap to give a little longer display, or use the 555 to create 1 long pulse that triggers something more digital and interesting. Either way, at that point, you have the digital pulse to play with and build more if you get bored without having to rewire... BETTER YET, wire the detectors up from the battery cases to batteries in the house where you can replace the batteries without ever going there! Monitor the V on each as you see fit. Even run them all off something rechargeable and trickle charged or super caps. Never worry about it again! Regulate down a 12v lead SLA battery and isolate each. QED. -Skip M. Adam Davis wrote: > Unless you (or the installer's) time is worthless, it's probably > cheaper in the long run to simply implement a scheduled replacement of > all the batteries. > > Do it twice a year. If any unit is dead when you do it, replace the > unit with a more efficient unit that lasts 6+ months on a single > battery. Buy the batteries in bulk. > > Then you spend only 2 hours a year replacing batteries, rather than > going down every month for 30 minutes finding and replacing the one or > two dead batteries that failed that month for 6 hours a year. It's > also a good savings if any project you undertake to simplify it still > requires you to go down there every month for at least 10 minutes a > month replacing batteries, nevermind the 40+ hours you'll spend > implementing the project. > > If you like, build a bunch of ultra low power led drivers to use up > any remaining energy on the cells you remove and hand them out as > "emergency candles" during power outages. > > But if you really must pursue a project for it, I'd look into putting > two+ microphones into the space and using a phase detector to get the > location of the beep. This won't require you to modify the units at > all, and will be a very interesting project to pursue that has a lot > of other applications once you understand the basics of position > sensing via sound. > > Even if it narrowed the location of the beep to within 20 feet it > would save you a lot of time. > > On Sun, Nov 29, 2009 at 6:11 PM, YES NOPE9 wrote: > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist