On Sat, Jan 25, 2014 at 8:39 PM, Charles Craft wr= ote: > I'm building a PIC data logger that will run from a wall wart. > During a power outage I would like it to stay alive for an hour or maybe = two. > > It's a one off for me at this time so cost and board space are not an iss= ue. > I'm looking for simple and safe. Thoughts? > > thanks > chuckc I think a beefy super cap would be the way to go. The only thing to be aware of is the momentary inrush current required to charge it may be quite high, perhaps heating the voltage regulator or causing excessive turn on times for the MCU (their is a datasheet spec which requires the voltage to raise faster than a certain rate for proper operation). However, those are pretty trivial issues to deal with. The big deciding factor is the current consumption of your circuit. If you haven't already, I would suggest working to optimize it for power consumption. Operating buzzers, LEDs, Displays, and not going putting the MCU in sleep mode when it's idle will burn through your backup supply quickly. Super Cap: Pros: Simple to implement and usually durable if used within specs Cons: potentially high inrush currents, somewhat limited storage capacity for cost (likely not a problem for your application's spec) Batteries: Pro: Cheap for Large storage capacity (easily more than a just a few hours of runtime depending upon current usage) Con: Batteries require properly implemented recharging circuits to be safe and will wear out requiring replacement after a limited number of cycles. USD $3.60, 1.5F 5.5V Supercap http://www.digikey.com/product-detail/en/DB-5R5D155T/604-1151-ND/3280644 datasheet http://www.elna.co.jp/en/capacitor/double_layer/catalog/pdf/dbn_e.pdf --=20 Jason White --=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 .