Post by thread:[EE]: [PIC]: Any ideas on backup battery switchove

on 3/13/01 6:14 AM, Byron A Jeff at spam_OUTbyronTakeThisOuTCC.GATECH.EDU wrote: > I'm open to any other ideas. I'm facing a related problem: how to keep my PIC powered long enough in the absence of line power. I bought a couple of super caps (5V, 1.5 F) originally to power a clock chip that was designed for this. But I've moved the clock functionality into the PIC (a 16F877), so now I need to keep power to the PIC. I think what I'll do is find a way for the PIC to monitor main power, and then just go into sleep if that falls below some level. The super cap can probably be wired straight to Vdd with steering diodes to keep it from powering the rest of the circuit. Then I'll wire RB0/INT to the supply outside the diode, and if that level falls from high, it can generate an interrupt to execute code to handle sleep. I, too, would appreciate any comments. ------------------------------------------------------------ Roderick Mann .....rmannKILLspam@spam@latencyzero.com.sansspam -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> > on 3/13/01 6:14 AM, Byron A Jeff at byronKILLspamCC.GATECH.EDU wrote: > > > I'm open to any other ideas. > > I'm facing a related problem: how to keep my PIC powered long enough in the > absence of line power. I bought a couple of super caps (5V, 1.5 F) > originally to power a clock chip that was designed for this. But I've moved > the clock functionality into the PIC (a 16F877), so now I need to keep power > to the PIC. > > I think what I'll do is find a way for the PIC to monitor main power, and > then just go into sleep if that falls below some level. The super cap can > probably be wired straight to Vdd with steering diodes to keep it from > powering the rest of the circuit. Then I'll wire RB0/INT to the supply > outside the diode, and if that level falls from high, it can generate an > interrupt to execute code to handle sleep. > > I, too, would appreciate any comments. Well first off I'd run a couple of tests and see how long the supercap drives the 16F877. Honestly the difference between sleep and not sleep isn't much. BAJ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

From my recollection, those super caps have pretty high internal resistance and my not be able to give you the current you need to run a PIC. Make sure to check it out. Ron Rick Mann wrote: {Quote hidden}> on 3/13/01 6:14 AM, Byron A Jeff at .....byronKILLspam.....CC.GATECH.EDU wrote: > > > I'm open to any other ideas. > > I'm facing a related problem: how to keep my PIC powered long enough in the > absence of line power. I bought a couple of super caps (5V, 1.5 F) > originally to power a clock chip that was designed for this. But I've moved > the clock functionality into the PIC (a 16F877), so now I need to keep power > to the PIC. > > I think what I'll do is find a way for the PIC to monitor main power, and > then just go into sleep if that falls below some level. The super cap can > probably be wired straight to Vdd with steering diodes to keep it from > powering the rest of the circuit. Then I'll wire RB0/INT to the supply > outside the diode, and if that level falls from high, it can generate an > interrupt to execute code to handle sleep. > > I, too, would appreciate any comments. > > ------------------------------------------------------------ > Roderick Mann EraseMErmannspam_OUTTakeThisOuTlatencyzero.com.sansspam > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics