On Mon, Nov 7, 2016 at 5:13 AM, RussellMc wrote: > In retrospect and with greater surrounding knowledge that is "clear > enough", BUT even now the information is incomplete and you did not answe= r > the questions seeking clarification, and the exact requirement is still > unclear. > Which clarification questions have I missed? I already answered that it's a LiPo battery. If it helps at all, the spec I have which I might not have mentioned before is that the kit has both an external battery and an internal battery. If the external battery is left plugged in it will completely run down and never switch to the internal battery. If you unplug the external battery when it is almost run down, then it will switch to the internal battery so resulting in another 24 hours of runtime. My friend is after a way to automatically disconnect the external battery in the same way as unplugging it does when it drops below a certain voltage. Though I don't think that level of detail makes any difference to the question. > Does this seem overly pedantic? > To some extent yes, because the realistic answer to most of the questions is "it doesn't matter". I did suggest use of a FET in my OP and that's the spec people seem to be going with for "disconnect" - which is exactly what I intended. I don't think the actual battery chemistry makes the slightest difference to the spec, and whilst the voltage and current are clearly important for precise specification I was after general ideas and quite capable of adjusting designs for different voltage and current specs (I didn't have that info when I first asked, I've passed it on as soon as I did, though it already clarified things for me). I appreciate you don't know my background, but I have for example designed and built my own PIC controlled battery charger for charging both LiIon and NiMH batteries which incorporates a similar cutoff based upon sensing voltage and current. So I don't totally need my hand holding, but then I didn't have experience of this particular circuit - and have only ever done analogue electronics on a hobby basis or for test stuff in work (I've worked on things with analogue including proper production stuff, but only ever done the digital/firmware side) - if this was just a one off I'd happily hack something, but given the context I was interested in generic ways to do it properly. The proof of the pudding being in the eating, one of the early replies came up with the TL431 circuit which is what it will probably end up using - it's only the addition of hysteresis which was required, and all of the replies have been useful, even those telling me I asked the wrong question! I don't think anybody has been confused by the spec and gone off down a rabbit hole - if anything I have more useful information than if I'd been tighter in the specification (I don't think the diode will be the correct solution, but it's certainly something which is worth investigation, and I might not have got that suggestion). Anyway a bit of going off on a tangent makes for more interesting threads on here that just "do my homework" questions. Thanks all, 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 .