On 6/4/2011 5:43 PM, V G wrote: > On Sat, Jun 4, 2011 at 5:26 PM, Michael Watterson wro= te: > >> no point. The pad needs a cable. >> > That's fine. The pad can stay plugged in. > > >> Why not just have a USB socket *and* a 2.5mm power jack for charging. >> Then anything can charge it. >> Use 2 x AA cells, so if flat a pair of Alkalines can be temporarily be >> substituted. >> >> I find it very handy that my camera and radios can take Alkaline >> batteries in an emergency. > > So I'd then use two AAA batteries, the same switching supply, but I'm > assuming that for a device like this, the end user is too lazy to keep > charged or properly maintained. So I'm trying to find the most selft > maintaing solution possible. Solar would be best if it provided enough > energy under room light conditions. Inductive is the next best thing. > Anything that requires it to be plugged in isn't so great because I doubt= my > /clients/ would care enough to plug it in. I wonder if the clients do gigs or studio. I like to throw the tuner=20 in the guitar case. Not much light there. Maybe you could build a=20 light source into the case and plug it in! Sorry to not have useful suggestions. It sounds like a challenging=20 problem that needs a circuit as low power as a solar powered=20 calculator. Even they take a while to come to life after long dark periods= .. Joe --=20 Joe Wronski Stillwater Embedded Engineering www.stillwatereng.net --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .