10F and a p fet 3 parts ! and I am pretty sure that one of the 10F's has a 1.2v bandgap reference worse case add two resistors S=20 -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of Chris McSweeny Sent: 06 November 2016 18:07 To: Microcontroller discussion list - Public. Subject: Re: [EE] Really simple cutoff circuit http://www.batterysupports.com/queclink-gps-tracker-gl200-gl300-gl300w-3400= m ah-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 a= t 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=20 >> bad in quantity (10F320 ~ NZ$0.70 @ 100) >> > > Hmm - I don't think the price of that would be a problem -=20 > realistically the cost of components is likely to be dwarfed by the=20 > build costs whichever way we go. It would certainly be straightforward=20 > to avoid the oscillation problem which I think would be an issue with=20 > most or all of the other proposed circuits. Not really sure why I=20 > didn't think of that when posting to a PIC list (though I suspect I'd=20 > probably go with an AVR as I have more recent experience of those, so=20 > the dev would be a lot quicker). Not that it would reduce the part=20 > count much - it would still need a potential divider on the input,=20 > 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=20 > assume less than 100mA because it's for something which would last=20 > many hours with a fairly small battery. I'm not sure of the battery=20 > chemistry and hence max voltage or quiescent current requirements=20 > (though I'm expecting quiescent current not to be a big problem) - the=20 > only spec I've been given is a 4.5V cutoff. Will get some more details in order to spec this better. > > Some more details - it's for an external battery for a tracking=20 > device, to be used in an event which lasts up to 7 days - though the=20 > battery will get switched over during that, so I'm not sure of the=20 > expected duration. Needs to be small, light and simple - I don't think=20 > pressing a button to enable it is likely to be a good idea, it needs=20 > to be fully automatic when plugged in. > > Thanks for all the info so far - it seems I wasn't too far off with my=20 > initial thoughts, though it's good to get better suggestions. > > Chris > -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=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 .