-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Fri, Nov 16, 2007 at 09:33:02AM -0500, Timothy J. Weber wrote: > - An interesting solution to the same power switch problem I was > studying with this project: (also a > 2xAA switcher for a portable device). Olin's solution uses less weird > hardware and cleverer firmware. I think I was obsessing about having > "no" current flowing while off; he's settled for "negligible" and made a > much more elegant solution in the process - fewer parts, more > flexibility in what's required for power-on. I like it. I gotta agree with him too. I've designed two devices now that are fully sealed after manufacture, and need a one time activation to do their thing. After asking about no power latch circuits here on piclist, I settled with just having a pic in sleep mode waiting for that first button press. Both times I implemented the turn on with a reed switch and the turn on logic was that the reed switch had to be held closed by a magnet for 10s before ativation happened. The only problem I found was reed switches need the magnet fairly close to them to actually activate, for a device embedded in epoxy or acrylic it's tough to position them close enough. I'm thinking about ditching that setup for something a little more involved, but without magnet, namely mechanical tilt switches. Rotate the unit in a defined series of actions with timing. Problem is, as far as I can tell buying mechanical tilt switches is damn near impossible now. All digikey has is either very large ones for more industrial uses, or smaller photo sensor/hall effect based ones with current consumptions of at least 10uA, if not 20ma. Hmm... Just occured to me though... If you don't want your sensor to drain your battery, why not use a sensor that generates electricity for you? As in... solar. Looking at digikey I just noticed they have tiny solar cells in 8 and 16 pin SOIC packages for sensing and (according to the datasheet) trickle charging. With a 50uA short circuit current that big lead acid might take a few decades, but it would be enough to bootstrap a uC. That, or use one with one of the above 10uA tilt sensors! It'd make sure the device wasn't accidentally turned on during shipping! In any case, our Randy Glenn has one of those devices.. You turned it on yet? :) - -- http://petertodd.org -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFHP0b83bMhDbI9xWQRAgQ8AJsE9+zvmk2ArXfVuW+vvjGlor3L5ACgkFj+ e5Wp0iqqasz9p7uK2Wp9kII= =svJq -----END PGP SIGNATURE----- -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist