http://www.batterysupports.com/queclink-gps-tracker-gl200-gl300-gl300w-3400= mah-external-battery-p-481.html - so I was wrong about 4.5v cutoff. That does look like it already has a circuit which should do this, but apparently it doesn't, so we're looking at 3v cutoff (and 4.2v max). Current draw as I suggested before - a 1700mAh battery will do 24hrs, so ~70mA. Thanks, Chris On 6 Nov 2016 15:19, "Chris McSweeny" wrote: > On Sun, Nov 6, 2016 at 12:50 PM, IVP wrote: > >> How about a PIC10F with ADC ? Economy vs discretes might >> not be too bad in quantity (10F320 ~ NZ$0.70 @ 100) >> > > Hmm - I don't think the price of that would be a problem - realistically > the cost of components is likely to be dwarfed by the build costs whichev= er > way we go. It would certainly be straightforward to avoid the oscillation > problem which I think would be an issue with most or all of the other > proposed circuits. Not really sure why I didn't think of that when postin= g > to a PIC list (though I suspect I'd probably go with an AVR as I have mor= e > recent experience of those, so the dev would be a lot quicker). Not that = it > would reduce the part count much - it would still need a potential divide= r > on the input, something to drop the input voltage within range and an > output FET. > > In answer to some of the queries, current requirement is low - I'd assume > less than 100mA because it's for something which would last many hours wi= th > a fairly small battery. I'm not sure of the battery chemistry and hence m= ax > voltage or quiescent current requirements (though I'm expecting quiescent > current not to be a big problem) - the only spec I've been given is a 4.5= V > cutoff. Will get some more details in order to spec this better. > > Some more details - it's for an external battery for a tracking device, t= o > be used in an event which lasts up to 7 days - though the battery will ge= t > switched over during that, so I'm not sure of the expected duration. Need= s > to be small, light and simple - I don't think pressing a button to enable > it is likely to be a good idea, it needs to be fully automatic when plugg= ed > in. > > Thanks for all the info so far - it seems I wasn't too far off with my > initial thoughts, though it's good to get better suggestions. > > Chris > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .