[Elecraft] Leds for W1
Dave Van Wallaghen
w8fgu at comcast.net
Fri Feb 20 13:33:10 EST 2009
Hey Doug,
Looks like you are neck deep in this ;-)
Looking at the datasheet for the PIC16F876a, it states each I/O line can
sink 25ma. Looking at the schematic for the W1, I see 2k resistors in
series with each I/O line and the LED which is then banked through a
2n7000. If (and a big if) I did some math right, that would put a max of
2.5ma available to each line.
As this is a battery operated unit, keeping the current draw down would
be a good design consideration. And at a low current like 2.5ma, that
small difference in forward voltage would probably be the difference
you'd see visually. Not to mention that the I/O lines driving the LED
banks may very well pulsed with some type of duty cycle out of visual
range (just guessing here).
I don't know if in the end, I would be bothered too much by the visual
difference of the red leds in that I guess I would want the red ones to
grab my attention. On the other hand, Tom, N5GE's suggestion to replace
the red ones also (at least on the SWR bank) so they are consistent
might be a good compromise.
I have the same Digi-Key catalog and see what you are talking about. I
will go back to the Mouser #'s Bill posted here and cross reference them
with Digi-Key and see if the operating stats are more consistent.
Thanks for the hard work,
Dave W8FGU
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_joyce at sympatico.ca>
> *To:* Dave Van Wallaghen <mailto:w8fgu at 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:k0pp at rfwave.net>
> *To:* w8fgu at comcast.net <mailto:w8fgu at comcast.net> ; Doug Joyce
> <mailto:d_joyce at sympatico.ca> ; elecraft at mailman.qth.net
> <mailto:elecraft at 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
>
>
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