On May 25, 9:01=A0pm, cbarn24...@aol.com wrote:> First off 25mA is going to give you a dim display unless you are > useing low current leds.I'm going to try get my hands on LED's that are bright in natural daylight. Do you think I'd get much performance out of any such LED's for 25 mA.> ULN200x chips were designed to drive 7Seg led > displays, so a perfect choice for you. PNP bjts are cheapest and > simplest for the rows. You seem to have the rows/colomns mixed upThe rows are coming straight from the =B5C pins (the PIC16F684 pins can source and sink 25 mA).
Most suitable driver chip
Started by ●May 22, 2008
Reply by ●May 25, 20082008-05-25
Reply by ●May 25, 20082008-05-25
On Sun, 25 May 2008 15:19:48 -0700 (PDT), the renowned Tom�s � h�ilidhe <toe@lavabit.com> wrote:>On May 25, 9:01�pm, cbarn24...@aol.com wrote: > >> First off 25mA is going to give you a dim display unless you are >> useing low current leds. > > >I'm going to try get my hands on LED's that are bright in natural >daylight. Do you think I'd get much performance out of any such LED's >for 25 mA.Average current per LED is?>> ULN200x chips were designed to drive 7Seg led >> displays, so a perfect choice for you. PNP bjts are cheapest and >> simplest for the rows. You seem to have the rows/colomns mixed up > > >The rows are coming straight from the �C pins (the PIC16F684 pins can >source and sink 25 mA)."Can" as in "absolute maximum rating", which is a rather foolish thing to aim for in a serious design. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Reply by ●May 26, 20082008-05-26
On May 26, 12:11=A0am, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> wrote:> >I'm going to try get my hands on LED's that are bright in natural > >daylight. Do you think I'd get much performance out of any such LED's > >for 25 mA. > > Average current per LED is?I don't know, I haven't picked the LED's yet. What I was asking about was whether 25 mA would be enough to light any LED bright enough to be seen in daylight (any LED on the market, that is)?> >The rows are coming straight from the =B5C pins (the PIC16F684 pins can > >source and sink 25 mA). > > "Can" as in "absolute maximum rating", which is a rather foolish thing > to aim for in a serious design.I don't understand your reasoning here. A spec sheet might say "Source and sink maximum current =3D 25 mA". If I'm not mistaken, this means that it's perfectly OK to put 25 mA thru them. If there was a need to undercut this figure by 10%, then surely it would make more sense if the spec sheets reduced their values by 10%. Does anyone else see a problem with taking 25 mA from a microcontroller pin that's rated for 25 mA maximum?
Reply by ●May 26, 20082008-05-26
On May 26, 10:23 am, donald <Don...@dontdoithere.com> wrote:> Tom=E1s =D3 h=C9ilidhe wrote: > > > Does anyone else see a problem with taking 25 mA from a > > microcontroller pin that's rated for 25 mA maximum? > > I would look at the data sheet directly and see what is says. > > Is this micro-controller a secret ? > > Lets all take a look at the data sheet involved and see if this > micro-controller would have a problem with this. > > donaldI read 25mA max per pin and 90mA max per chip. Namely, no more than 3 leds on at any time.
Reply by ●May 26, 20082008-05-26
Tom�s � h�ilidhe wrote:> > Does anyone else see a problem with taking 25 mA from a > microcontroller pin that's rated for 25 mA maximum?I would look at the data sheet directly and see what is says. Is this micro-controller a secret ? Lets all take a look at the data sheet involved and see if this micro-controller would have a problem with this. donald
Reply by ●May 26, 20082008-05-26
On May 24, 6:38=A0pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> wrote:> On Mon, 26 May 2008 09:26:34 -0700 (PDT), linnix > > > > > > <m...@linnix.info-for.us> wrote: > >On May 26, 10:23 am, donald <Don...@dontdoithere.com> wrote: > >> Tom=E1s =D3 h=C9ilidhe wrote: > > >> > Does anyone else see a problem with taking 25 mA from a > >> > microcontroller pin that's rated for 25 mA maximum? > > >> I would look at the data sheet directly and see what is says. > > >> Is this micro-controller a secret ? > > >> Lets all take a look at the data sheet involved and see if this > >> micro-controller would have a problem with this. > > >> donald > > >I read 25mA max per pin and 90mA max per chip. =A0Namely, no more than 3 > >leds on at any time. > > http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf > > I see Abs. Max 25mA/port pin and 200mA max combined port A and C,And a 95mA max Idd and Iss, so you can't do more than 95mA absolutely.
Reply by ●May 26, 20082008-05-26
On May 24, 6:58 pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> wrote:> On Mon, 26 May 2008 10:46:14 -0700 (PDT), linnix > > > > <m...@linnix.info-for.us> wrote: > >On May 24, 6:38 pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> > >wrote: > >> On Mon, 26 May 2008 09:26:34 -0700 (PDT), linnix > > >> <m...@linnix.info-for.us> wrote: > >> >On May 26, 10:23 am, donald <Don...@dontdoithere.com> wrote: > >> >> Tom=E1s =D3 h=C9ilidhe wrote: > > >> >> > Does anyone else see a problem with taking 25 mA from a > >> >> > microcontroller pin that's rated for 25 mA maximum? > > >> >> I would look at the data sheet directly and see what is says. > > >> >> Is this micro-controller a secret ? > > >> >> Lets all take a look at the data sheet involved and see if this > >> >> micro-controller would have a problem with this. > > >> >> donald > > >> >I read 25mA max per pin and 90mA max per chip. Namely, no more than 3=> >> >leds on at any time. > > >>http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf > > >> I see Abs. Max 25mA/port pin and 200mA max combined port A and C, > > >And a 95mA max Idd and Iss, so you can't do more than 95mA absolutely. > > Where are you getting that number from? On page 127 (PDF page 129) > > Abs. max Idd is 250mA > Abs. max Iss is 300mA > Abs. max current sunk by PORTA and C combined 200mA > Abs. max current sourced by PORTA and C combined 200mAPage 131 of http://ww1.microchip.com/downloads/cn/DeviceDoc/cn011811.pdf That's strange. Are we looking at the same chip, PIC16F684?
Reply by ●May 26, 20082008-05-26
On May 26, 11:35 am, linnix <m...@linnix.info-for.us> wrote:> On May 24, 6:58 pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> > wrote: > > > > > On Mon, 26 May 2008 10:46:14 -0700 (PDT), linnix > > > <m...@linnix.info-for.us> wrote: > > >On May 24, 6:38 pm, Spehro Pefhany <speffS...@interlogDOTyou.knowwhat> > > >wrote: > > >> On Mon, 26 May 2008 09:26:34 -0700 (PDT), linnix > > > >> <m...@linnix.info-for.us> wrote: > > >> >On May 26, 10:23 am, donald <Don...@dontdoithere.com> wrote: > > >> >> Tom=E1s =D3 h=C9ilidhe wrote: > > > >> >> > Does anyone else see a problem with taking 25 mA from a > > >> >> > microcontroller pin that's rated for 25 mA maximum? > > > >> >> I would look at the data sheet directly and see what is says. > > > >> >> Is this micro-controller a secret ? > > > >> >> Lets all take a look at the data sheet involved and see if this > > >> >> micro-controller would have a problem with this. > > > >> >> donald > > > >> >I read 25mA max per pin and 90mA max per chip. Namely, no more than=3> > >> >leds on at any time. > > > >>http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf > > > >> I see Abs. Max 25mA/port pin and 200mA max combined port A and C, > > > >And a 95mA max Idd and Iss, so you can't do more than 95mA absolutely. > > > Where are you getting that number from? On page 127 (PDF page 129) >OK, your link is dated 2004: http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf> > Abs. max Idd is 250mA > > Abs. max Iss is 300mA > > Abs. max current sunk by PORTA and C combined 200mA > > Abs. max current sourced by PORTA and C combined 200mA >My link is dated 2007:> Page 131 ofhttp://ww1.microchip.com/downloads/cn/DeviceDoc/cn011811.pdf > > That's strange. Are we looking at the same chip, PIC16F684?So, I won. This is progress (LOL). Probably process shrink.
Reply by ●May 27, 20082008-05-27
linnix wrote: <snip>>>>And a 95mA max Idd and Iss, so you can't do more than 95mA absolutely. >> >>>Where are you getting that number from? On page 127 (PDF page 129) >> > > OK, your link is dated 2004: > http://ww1.microchip.com/downloads/en/devicedoc/41202C.pdf > > >>>Abs. max Idd is 250mA >>>Abs. max Iss is 300mA >>>Abs. max current sunk by PORTA and C combined 200mA >>>Abs. max current sourced by PORTA and C combined 200mA >> > > My link is dated 2007: > > >>Page 131 ofhttp://ww1.microchip.com/downloads/cn/DeviceDoc/cn011811.pdf >> >>That's strange. Are we looking at the same chip, PIC16F684? > > So, I won. This is progress (LOL). Probably process shrink.Maybe, tho that is a newish device. It could also mean they found the 95mA was all the part was reliable to. Not the first time a device has been 'derated' following field feedback ! -jg
Reply by ●May 27, 20082008-05-27
