> Google has a better memory than me for such things, but from memory, > hard short on data lines indicates a high current source. Memory may > want. >=20 > On Apples implementation you can set various voltages on D+ and D- > with resistive dividers to convey charging information. >=20 > >From (the same) memory there are some resistor value in the new USB > phone charging spec that allow 'dumb' units to request various > currents. >=20 Thanks for the info. Will have to google some more here I think. I am plann= ing=20 to use a PIC32 with internal USB. Perhaps it already has circuits to detect= =20 some of those conditions? > I would not rely on onboard cell protection circuitry for low voltage > cutoff. This is the worst case level. By setting it somewhat higher > you get very little loss in capacity but sigmificantly extend battery > life. An eg TL431 and a very little glue parts will give you low > voltage protection. > So, perhaps a 2.75V cutout circuit and a 2.9V LDO for the core digital logi= c.=20 There will also be a way of measuring the cell voltage to provide a low vol= tage=20 warning at about 3V. I am a bit worried about the current used by the cutout regulator by itself= - I=20 suspect I need some aditional circuitry (an op perhaps) to provide for=20 hysteresis in order to prevent oscillation. This device may be used frequen= tly=20 during a limited period of time and then sit for months unused. I also need an RTC and was planning to keep it alive with backup power directly from the battery while the rest of the circuit is off. =20 > If you are using nipple ended LiIon cells be suer you can tolerate a > non LiIon cell in the battery holder. Alkaline / manganese zince are > easy enough to detect. If you use low current low voltage startup for > low Voltage cells (as you should ) then you can safely insert them and > at worst you will probabl;y just destroy them LiFePO4 is harder to > detect. (also available in 14500) > Use of tagged cells or of cells wit flat topped end caps and no nipple > - wityh nipple calle being rejected by the holder, will stop some > prob;ems - but not LiFePO4. >=20 Yes, I am planning to use an MCP73833 for charging which has undervoltage c= ell=20 detection and preconditioning for charging. I am not too worried about batt= ery=20 mixup since the battery will be inside a closed enclosure and hopefully wil= l=20 last for the lifetime of the device. Still, a battery holder allows an easy= =20 enough replacement possibility by the end customer. The 14500 size cells se= ems=20 easy enough to obtain. Not sure about this yet though, might still go for a= JST=20 connector, depending on how much room there will be when everything else is= in=20 place. >=20 > Russell McMahon > --=20 Thanks for the feedback. Appreciate it. While I can find lots of standalone= =20 reference charger circuits, it is a bit harder to find schematics for real= =20 devices communicating via USB while aslo powered and charged from USB. /Ruben =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Ruben J=F6nsson AB Liros Electronic Box 9124 200 39 Malm=F6 Sweden www.liros.se Tel +46 40142078 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .