Just a dumb question: are we sure that the power supply has the "oomf" to drive the tapestry? Maybe it is being loaded too much resulting in voltage drop. Perhaps it is even shutting down due to overcurrent or thermally? Should check voltage across the supply under load! -- Bob Ammerman RAm Systems =20 -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of KPL Sent: Thursday, January 24, 2013 2:02 PM To: Microcontroller discussion list - Public. Subject: Re: [EE] strange LED tapestry behaviour to mimick a battery pack, probably you could connect some resistor in series, maybe 100ohm, or a little bit less (depending how much current that circuit actually uses) Together with a capacitor at the supply end that would also eliminate any short high voltage spikes, if those exist. On Thu, Jan 24, 2013 at 12:48 AM, William Bulley wrote: > According to IVP on Wed, 01/23/13 at 15:29: >> >> A fresh alkaline is 1.65V, so 3 would be as high as 4.95V (something=20 >> you learn when powering logic off of batteries) > > Wow! Amazing! Who'da thunk? :-) > >> Perhaps measure the battery voltage during operation and after the=20 >> unit stops working, also the current draw > > Okay, that sounds do-able. > >> Some designers are fiendishly clever, and can make a circuit work=20 >> within a narrow window but don't give a hoot about battery life > > Yes, tell me about battery life... :-( > >> Similar to what Sean mentioned, I've seen a lot of people over at the=20 >> laser LED sites using 2 batteries without active current limiting=20 >> ("just stick 3V on it, you'll be fine"). There's 3V, and then there's=20 >> 3V > > Heh... :-) > >> Ideally you'd want to characterise your tapestry with a PSU that has=20 >> voltage and current settings. You can make a basic one with a couple=20 >> of LM317s. One sets the voltage, another sets the current >> >> http://www.ti.com/lit/ds/symlink/lm117.pdf > > Very nice. Thanks! Boy that reference sure takes me back! :-) > >> Worth having a few in the parts box. Figure 36 shows how you use one=20 >> as a current limiter - as an alternative to a resistor - to simulate=20 >> the battery impedance > > I believe I do have a few in my parts box. Lots of reading to do... =20 > :-) > > Thanks again! > > Regards, > > web... > > -- > William Bulley Email: web@umich.edu > > 72 characters width template=20 > ----------------------------------------->| > -- > http://www.piclist.com PIC/SX FAQ & list archive View/change your=20 > membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- KPL -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membershi= p options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .