I have some experience driving LEDs from a PIC (both in my book Programming the PIC Microcontroller with MBasic) as well as the Z100 CW tuning aid kit that I developed. (Still available, should anyone be interested, as well as the book is still in print.)
The Z100 uses red, yellow and green rectangular LEDs, driven from a PIC with a small series resistor. http://www.cliftonlaboratories.com/z100_tuning_aid.htm for more details. For all practical purposes, a PIC won't source more than about 20 mA even into a short circuit. Looking at the W1's schematic (I don't own one) it seems that the maximum current available to drive an LED is around 1.5 mA (5V from the PIC, less 2V drop for the LED average, with 2K ohm series from the PIC output. The 2N7000's on resistance can be ignored in this calculation.) That's quite low current, and it should be possible to boost it--and the LED's brightness--considerably by reducing the 2K series resistors. My experience is that although perhaps not designed that way, PICs are pretty abuse tolerant in the output mode. My Z100 drives the LEDs through 43 ohm resistors and the LEDs are quite bright. The Z100's typical LED driving current is around 10 mA if I remember the measurements correctly. A couple of caveats - the Z100 does not run with all the LEDs illuminated under normal conditions. With noise, perhaps three or four are at at maximum, and with a signal input, one or two. Hence the Z100's+5V regulator is not designed to provide oodles of current. Second, there is a dissipation limit on how much total current a PIC can source from all pins. If the W1 operates in a mode where most LEDs are on for extended periods, I would evaluate the 5V regulator's thermal performance and also the PIC's maximum power dissipation before getting carried away with reducing the series driver resistors. As usual, should anyone destroy their W1 through making these changes, you are on your own. Jack K8ZOA www.cliftonlaboratories.com Doug Joyce wrote: > Dave / Ken: > > Further to the attached: > > Gary provided the info on the Red LED as "the Digi-key part# is > 516-1281-ND & the Mfg is Avago Tech part # HLMP-S100." > > This part is listed in the Digi-Key T091 (Jan - Apr 2009) catalogue, > page 2615. The same section also lists two green LEDs, the brighter > is Digi-Key part # 516-1285-ND (Avago part # HLMP-S501). > Interestingly enough the T081 catalogue (page 2455) also listed a > "yellow" from the same series as Digi-Key part # 516-1284-ND (Avago > part # HLMP-S301), but when I tried to get a quote, the minimum order > qty was over 5000 units. Orange is also made by Avago as part > # HLMP-S401 (same Digi-Key part No.) with a minimum order qty of 3,000 > units. So green seems to be the only other LED from the same Avago > family available in reasonable quantities. (The Mouser part numbers > for the Avago Tech LEDs are 630-HLMP-Sxxx etc) > > For the "red" LED Luminous intensity is given as 7.5 mcd @ 20 ma with > a fwd voltage drop of 1.8 volts; however for the "green" (S501) the > specs are 8 mcd @ 20 ma with a fwd voltage drop of 2.2 volts. I > suspect that this 0.4 volt difference may be the cause of the > difference in intensity when installed in the W1. > > As for yellow and orange / amber LEDs from an alternate supplier, the > same T091 catalogue, page 2557 shows LEDs from Lumex. > "Yellow" is Digi-Key part # 67-1050-ND (Lumex part # SSL-LX2573-YD). > Fwd voltage drop of 2.1V & luminosity of 10 mcd; and > "Amber" is Digi-Key part # 67-1045-ND (Lumex part # SSL-LX-2573-AD). > Fwd voltage drop of 2.0 & luminosity of 5 mcd > (The Mouser part numbers for the Lumex LEDs are 696-SSL-LX2573xxx etc). > > I ordered a qty of > 526-1285-ND (HLMP-S501) , green from Avago and > 67-1050-ND (SSL-LX2573-YD), yellow from Lumex and > 67-1045-ND (SSL-LX2573-AD), amber from Lumex > > Connected to a 12V supply with a resistor to limit the current to 20 > ma, the intensity seems to be similar in all LEDs (including the > original red one). When installed in the W1 however, it's a > different story. (See my comment in the email below.) All of the > other colours are significantly less bright than the original "red" ones. > > Perhaps someone who has worked with the PIC microcontroller might be > able to suggest a solution. > > 73 > > Doug, VE3MV > > > ----- Original Message ----- > *From:* Doug Joyce <mailto:d_jo...@sympatico.ca> > *To:* Dave Van Wallaghen <mailto:w8...@comcast.net> > *Sent:* Friday, February 20, 2009 9:11 AM > *Subject:* Leds for W1 > > Dave: I'm not sure the email I cc'd you on earlier got sent, so > here is a resend. > > Ken / Dave: Just to let you know, I did this with equivalent / > the same parts (I'll provide the part numbers I used later this > AM) and at 20 ma fwd current they do indeed seem to all have > equivalent brightness. The problem I found is that when installed > in the W1, they don't light up with the same intensity as the red > ones supplied. I used other colours of green, yellow and amber / > orange. > > I haven't spent a lot of time to investigate, but what I found so > far is that the fwd voltage drop on the red LEDs is smaller than > on the other colours, and in the W1 cct it is a smaller percentage > of the supply voltage of 5 volts. This results in more fwd > current that available for the red compared to the other colours, > hence the red appears to be brighter. The next step I need to do > is to actually measure the current provided by the W1 for these > other colours. > > I got 10 of each when I ordered then from DigiKey - Dave, if you > provide your mailing address, I'll send you a couple of each and > you can try then in the W1 as well. > > 73 > > Doug, VE3MV > > > > > > ----- Original Message ----- > *From:* Ken Kopp <mailto:k...@rfwave.net> > *To:* w8...@comcast.net <mailto:w8...@comcast.net> ; Doug > Joyce <mailto:d_jo...@sympatico.ca> ; elecraft@mailman.qth.net > <mailto:elecraft@mailman.qth.net> > *Sent:* Thursday, February 19, 2009 10:52 PM > *Subject:* Re: [Elecraft] W1 LED Part Numbers > > I have a "set" of additional green and yellow LED's > from Scott at Aptos. He got them for me from the > stock bins and didn't include their stock numbers. > > I'll light them with a PS and see if their all the same > brightness and take a photo. > > They -should- be the same product line and therefore > light equally, I'd think. They're from the KAT-100 > tuner. > > Scott was at least receptive to making all the W1 > kits with three colors of LED's. > > 73! Ken > > > ------------------------------------------------------------------------ > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
