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Article #82Re: Best way to power array of LEDs?
From: Tony Williams
Date: Fri, 06 Dec 2002 08:41
Date: Fri, 06 Dec 2002 08:41
43 lines
3437 bytes
3437 bytes
In article <h48vuuordbt547u37tb38vpfivfqm2t0at@4ax.com>, Spehro Pefhany <speff@interlog.com> wrote: > On Thu, 05 Dec 2002 16:33:44 +0000 (GMT), the renowned Tony Williams > <tonyw@ledelec.demon.co.uk> wrote: > > 20mA > > +Supply---->----/\/\---+-----|>|---- 0v. > > | LED > > PIC port pin-----------+ > > > > Had this brilliant idea that could could turn > > the LED On/Off by toggling the port pin from an > > input, to an output at logic 0. > Aside from the obvious worry if TRIS or PORT latches > get flipped by noise, it should work, assuming > +Supply <= Vdd + 0.3 (except for the funky open > drain output w/o protection diodes that some of them > have). It's that warning in every PIC data sheet Speff. An output pin that is driven to 0/1 must be allowed to reach the correct 0/1 voltage. If not, undefined things happen during subsequent writes to that o/p. > Though I don't think Vout(low) is guaranteed at > 20mA, it should be low enough even for a red LED, > shouldn't it? (at least with the current crop) *cough* To compound the perp I see that I actually had 4x pins in parallel to short the LED to 0v. In the original software, the sequence of "set port- pins to logic 0, then set port-pins to outputs" resulted in the pins being set to logic 1, the LED lit up like a searchlight, with 130mA drawn off the 5v. Fortunately that 20mA could be gated-Off for a few uS. If that was done, then the original sequence worked correctly. -- Tony Williams.
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X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 112d1e,4ef4c9d4aea85e1f X-Google-Attributes: gid112d1e,public X-Google-Thread: 1131b0,4ef4c9d4aea85e1f X-Google-Attributes: gid1131b0,public X-Google-Thread: 103407,4ef4c9d4aea85e1f X-Google-Attributes: gid103407,public X-Google-Thread: 10d137,4ef4c9d4aea85e1f X-Google-Attributes: gid10d137,public X-Google-Thread: 1118be,4ef4c9d4aea85e1f X-Google-Attributes: gid1118be,public X-Google-ArrivalTime: 2002-12-06 00:45:46 PST Path: arc1-ca.pugleaf.net!archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!kibo.news.demon.net!news.demon.co.uk!demon!ledelec.demon.co.uk!tonyw From: Tony Williams <tonyw@ledelec.demon.co.uk> Newsgroups: sci.electronics.components,sci.electronics.design,alt.engineering.electrical,aus.electronics,sci.electronics.repair Subject: Re: Best way to power array of LEDs? Date: Fri, 06 Dec 2002 08:41:57 +0000 (GMT) Organization: None Lines: 43 Message-ID: <4ba080045etonyw@ledelec.demon.co.uk> References: <anku2n$5so$1@news.wave.co.nz> <7tGLdeAS6fn9EwBv@jmwa.demon.co.uk> <apvlvu$n2c$1@reader1.panix.com> <KVdHjAAjM3w9Ew8l@jmwa.demon.co.uk> <aq17gb$7ut$1@reader1.panix.com> <slrnasg1o7.1t5.Znospam+noZs_0211@hpb13799Z.Zboi.hpZ.com.invalid> <aseln1$jbb$1@reader1.panix.com> <Rm2H9.4457$5P3.213056@newsfeed.slurp.net> <4dqpuugil5jens3iu7uprml0hdjl5e5dqs@4ax.com> <4ba01ef90etonyw@ledelec.demon.co.uk> <c9ruuu87bn6t539n1se6ejueb1u1lia0j6@4ax.com> <4ba0275featonyw@ledelec.demon.co.uk> <h48vuuordbt547u37tb38vpfivfqm2t0at@4ax.com> NNTP-Posting-Host: ledelec.demon.co.uk X-Trace: news.demon.co.uk 1039164345 27535 194.222.56.201 (6 Dec 2002 08:45:45 GMT) X-Complaints-To: abuse@demon.net NNTP-Posting-Date: Fri, 6 Dec 2002 08:45:45 +0000 (UTC) User-Agent: Pluto/1.14i (RISC-OS/3.60)