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geekhack Projects => Making Stuff Together! => Topic started by: Photoelectric on Sat, 15 June 2013, 14:11:44

Title: Swapping indicator LEDs
Post by: Photoelectric on Sat, 15 June 2013, 14:11:44
Could anyone please point out a good place to get 2 replacement LEDs on the cheap that would be of proper rating and shape for a Filco Majestouch-2 TKL keyboard?  I'd like to replace 2 bright blue indicator LEDs with amber (or orange) LEDs that are not as blindingly bright.

Also, do I just desolder and swap out those LEDs or are there additional resistors to solder in as well to compensate for going from blue to red/amber?

ETA, it looks like the diameter of the stock LEDs is ~3mm... which is size T-1, if I'm correct.  I don't have a precision measuring tool, so I used  ruler :(  Looking on Mouser.com, but unsuccessfully so far, because I have no idea what "forward current" and "forward voltage" values I should be looking for.

Here's something--no idea if it's correct:
http://www.mouser.com/ProductDetail/Avago-Technologies/HLMP-NL06/?qs=sGAEpiMZZMtmwHDZQCdlqZihZ%252bOq2w4HmX66nGQmomc%3d

Stock Filco LEDs (seem to be in some plastic housing):

(http://i.imgur.com/t8kXhPu.jpg)
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Sat, 15 June 2013, 19:52:56
You're going to need to change a resistor along with the LED.
If you wanted the existing LEDs to be less bright, you could
swap in a bigger resistor (value, not physical size). The amount
of light coming off of a given LED is proportional to the amount
of current flowing through it. More resistance = less current.

In case you want to pick a new LED, and properly size the
associated resistor, here's how you'd do it:

Ohms law is what you need to calculate the amount of current.
V = I * R [Volts = Current (Amps) * Resistance (Ohms) ]
If your keyboard supplies 5v to the LED, some of that voltage
is dropped over the LED forward bias voltage - might be 3v
for your blue LEDs.  They might want 25mA (max) for a continuous
current. This means that I (The current term in your equation)
is 0.025A. So, the voltage over the diode is 3V, leaving 2V on
the resistor. the resistance then is R=V/I = 2/0.025 = 80 Ohms.

You might be happy to just swap in a 160 Ohms resistor to cut the
light output of the existing diode. 

If you use the amber LED you linked to, the forward voltage drop
is 2v. You might not want to give it the 20mA it could handle, and
might rather dim it down to say 7mA. This means that you need to
drop (5v - 2v) = 3v on the resistor at 7mA, so R = V/I = 3/0.007 = 429 Ohms.

Make sure to order a handful of resistors around the value you
might want - get a 150 Ohms, a 200, a 400, a 600, an 800, a 1k etc.
Then you can test them out to see which one results in the light
output level you're looking for.

Let us know how it goes!
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Sat, 15 June 2013, 21:23:00
Thank you for the detailed reply.  I'm just worried about frying the board / resistors by swapping in an improper combination of LED + resistor.  If I don't change the resistor from the stock one, and blue allows higher current, would it mean that if I just swap in the amber one I linked, it would burn out the amber LED?

Also, I'm definitely still interested if someone's replaced those Filco LEDs before and could confirm that the size I have is correct: 3mm or 1-T.
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Sat, 15 June 2013, 22:56:14
You're likely going to have to change the resistor in order to
prevent damaging the amber LED you'll be putting in there.
You'll be wanting to change the resistor in order to dim  the
LED anyhow...

If you only swapped the LED, it would likely work for a while...

Can you measure the voltage drop across the LED when it's on?

An easier solution might be to dab the existing LED with a
sharpie...  I did that last week to the distractingly bright LED
coming out of my touchpad when it is disabled.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Sat, 15 June 2013, 23:11:18
I don't have a voltmeter / multimeter at home, but I'll see about using one in a lab.  Looks like swapping these LEDs is not something commonly done here, so I'll have to plow through some research.
Title: Re: Swapping indicator LEDs
Post by: IvanIvanovich on Sun, 16 June 2013, 07:13:51
Generally blue is around 3.3v while amber is usually more like 1.8v so you will need to adjust the resistor for those. Yes those are 3mm led. Alternately, if you don't want to figure out resistor values, you can always get warm white (http://www.electron.com/led-3mm-warm-white-330pwo4c.html). Think that yellowy incandescent bulb look, it's not quite amber but it won't be harsh and mad bright.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Sun, 16 June 2013, 12:00:41
Thanks for that!!!

I've just looked at the LED area (still all soldered in, but I can look between the PCB and the plate), and it appears there's one resistor for both LEDs.  So I suppose the plan of action would be to desolder everything (which I'll do to change switches anyway), look at the resistor and try to identify it, and extrapolate the voltages that the blue LEDs are using.  From there, extrapolate what the replacement resistor would be for 2 amber LEDs.

The LEDs are in some white plastic housing.  I assume those are just "stand-offs" and serve no other function?
Title: Re: Swapping indicator LEDs
Post by: UniClown on Sun, 16 June 2013, 22:06:50
Quote from: Photoelectric on Sun, 16 June 2013, 12:00:41
The LEDs are in some white plastic housing.  I assume those are just "stand-offs" and serve no other function?

I would say so. I think they are just there to hold the LEDs at the right height.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 17 June 2013, 10:52:22
I contacted the Keyboard Company just in case, to see if they by chance had detailed specifications already, and here's what they said:

"You'll need to contact Diatec for detailed component info, different colour LED's need a different daughter board, the resistors at R8 and R9 change, near pin 17"

A different daughter board?..  to swap LEDs?..
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 17 June 2013, 12:56:38
Quote from: IvanIvanovich on Sun, 16 June 2013, 07:13:51
Generally blue is around 3.3v while amber is usually more like 1.8v so you will need to adjust the resistor for those. Yes those are 3mm led. Alternately, if you don't want to figure out resistor values, you can always get warm white (http://www.electron.com/led-3mm-warm-white-330pwo4c.html). Think that yellowy incandescent bulb look, it's not quite amber but it won't be harsh and mad bright.

I'll get a few of those Warm White LEDs to try out, they might actually look really nice with the case, even better than amber. 

Been looking at these ultraviolet LEDs too for a second Filco mod:
http://www.electron.com/led-3mm-ultraviolet-uv-330muv9c.html
Forward voltage is 3.5-3.8V.  Do you think that if they get ~3.3V they won't turn on or will just be very dim / barely visible?  I don't know if they are like fans and require a certain minimum "on" voltage.
Title: Re: Swapping indicator LEDs
Post by: WhiteFireDragon on Mon, 17 June 2013, 13:45:38
T1 or 3mm LEDs are the correct size. Ideally, you want to swap out resistors and put in ones that match the LEDs specs you want to use. However, removing the resistor on your Filco board requires special tools. First of all, all the components are on a daughterboard, and they're extremely tiny. It's SMD, so you'll have to desolder both ends of the resistor at the same time. This requires 2 irons, desoldering tweezers, or quikchip and braid.

Generally, LEDs on keyboards have a good enough tolerance where you can just swap out the LED without changing the resistors. If it's really out of spec, then it'll be too dim or too bright, or might even fry. They're cheap enough where you can just replace them though.

I bought ~6 types of amber color from mouser, and several types of white ones. Warm white and amber are very different colors. Most of my amber ones were pretty dim as well, and sometimes they're marked as "amber" but they're really orange.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 17 June 2013, 13:55:00
Thank you, WFD.  So I'd be fairly safe getting ~3.3V warm white and ultraviolet LEDs in 1T size without swapping the resistor?  I don't see any amber LEDs for that voltage range, unfortunately.  I was planning on swapping the resistor, but as you said it requires special equipment, and I only have a standard RadioShack desoldering tool.  Thus, I'm probably better off not touching the resistor(s).

I know warm white and amber are very different, but warm white would still fit the theme I'm going for quite well, perhaps even better than amber.  I spent a while looking at ultraviolet LED descriptions, and I know there's a difference in tone / brightness with different wavelengths, so I settled on these for my "Blue Filco" project:
http://www.mouser.com/Search/ProductDetail.aspx?R=UV3TZ-390-30virtualkey65330000virtualkey749-UV3TZ-390-30
(3.0-3.8V forward voltage range)

and the warm white LEDs that Ivan linked for the "Copper Filco" (3.2-3.6V)
http://www.electron.com/led-3mm-warm-white-330pwo4c.html

In theory, I'd desolder 2 solder joints per LED, pull out the LED + white / translucent housing, remove the LEDs from the housing, insert new LEDs, insert the LEDs + housing following proper polarity, resolder--correct?

Thanks again!  You are all extremely helpful.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 17 June 2013, 15:38:41
Oops scratch that... I read reverse voltage as forward voltage :(

Lol, $15.81 shipping for international priority mail to buy from electron.com...  for a few feather-light LEDs...
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Mon, 17 June 2013, 19:21:14
Quote from: Photoelectric on Mon, 17 June 2013, 12:56:38
Forward voltage is 3.5-3.8V.  Do you think that if they get ~3.3V they won't turn on or will just be very dim / barely visible?  I don't know if they are like fans and require a certain minimum "on" voltage.

If you don't exceed the forward voltage of the diode, you'll get no current to flow, and no light.
It seems probable that the supply voltage is > 3.8V, so you'll turn the diode on. You would then
just have less current flowing than with your 3.3V diode. This is what you're after anyhow in
order to dim the light... Go for it!


Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 17 June 2013, 19:24:33
Just ordered a bunch of different amber LEDs and a couple of UV LEDs.  I'll just plug them in without soldering and see how they look first.  What turns on and what doesn't, and how bright they are.
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Mon, 17 June 2013, 20:11:36
Just be sure to use sunglasses and sunscreen while using your keyboard if you go with the UV!
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 17 June 2013, 20:24:49
I always keep a tub of sunscreen on my desk for all those incident UVA rays from my windows!  Doesn't everyone?  :p
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 17 June 2013, 21:37:55
To desolder the LEDs, I need a very fine tip soldering iron / extension and a desoldering braid, right?  Those solder joints are tiny--definitely can't get them with a cheapo desoldering iron from Radio Shack.
Title: Re: Swapping indicator LEDs
Post by: IvanIvanovich on Thu, 20 June 2013, 19:13:21
LOL. Sorry I didn't even pay attention to where that place was located. I never bought nothing there, was just the first place I found to show what I was talking about.
I desolder 3mm led several times with my crappy radioshack stuff, it is fine. Only thing is with newer stuff, it will have rohs lead free solder, so it is more annoying for sure. Most of time you can put some lead/silver solder on it, then use the desolder iron and it is fine.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Wed, 26 June 2013, 20:00:53
Got a "real" soldering iron today and a good desoldering braid, and was finally able to get indicator LEDs out.  It's a good thing I got a bunch of different amber LEDs, as they are all different!  Some are quite a bit more orange, some are more sodium-lamp-yellow, some are transparent and look like an incandescent light bulb, and some are diffuse and encased in orange plastic.

Anyway, shot of my favorite yellow-amber so far

(http://i.imgur.com/7HPwm2h.jpg)

I'll try better photos at some point.

UV LEDs didn't light up at all.  Which is surprising, because they were completely within spec.  Also all of the amber LEDs are not as bright as the ultra-bright stock blue LEDs, which is great.  I thought they'd be brighter, given that they are running on higher voltage, but I guess not.
Title: Re: Swapping indicator LEDs
Post by: samwisekoi on Wed, 26 June 2013, 21:53:47
UV probably did work, and the fact that you couldn't see the light simply proves your humanity!

Good job.  I must do this to my scorchingly bright WASD keyboard LEDs.

 -  Ron I samwisekoi
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Wed, 26 June 2013, 22:09:26
Quote from: samwisekoi on Wed, 26 June 2013, 21:53:47
UV probably did work, and the fact that you couldn't see the light simply proves your humanity!

Good job.  I must do this to my scorchingly bright WASD keyboard LEDs.

 -  Ron I samwisekoi

Hah, that's exactly what my OH said :)  But seriously, I think the voltage is quite low across these LEDs.  I can't imagine it being ~3V+ because the amber LEDs are rated for ~2.2.-2.5V, and they were all not too bright.   Low voltage would also explain why the UV LEDs would not light up.  I wish I had a voltmeter to use :(  But it seems like the LEDs are getting around 2V.  Somehow the stock Filco blue LED is blindingly bright though, being blue at that.  I wonder if taking out that second stock LED will somehow decrease the resistance.  Unlikely, but I'll test tomorrow. 

Title: Re: Swapping indicator LEDs
Post by: bpiphany on Thu, 27 June 2013, 01:01:52
UV LEDs are not usually completely UV (probably so you'll see that they are on). But seriously. If you don't want to go blind, forget that you ever bought them.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Thu, 27 June 2013, 09:43:20
Their wavelength was within blue-purple optical range.  I believe UV was just a fancy name for them.

Bpiphany, with all of your hard work on programmable controllers (I have one in this very Filco!), have you had a chance to measure the voltage across Filco indicator LEDs?  Im confused why stock blue is so blindingly bright, but replacement amber are not (its a good thing, but I don't understand it, other than that it has to be lower voltage).
Title: Re: Swapping indicator LEDs
Post by: tgujay on Thu, 27 June 2013, 13:17:50
If I were to want to swap my Rosewill LED's for purple what resistors and LED's would I need?
Title: Re: Swapping indicator LEDs
Post by: bpiphany on Thu, 27 June 2013, 16:00:10
I actually don't remember if I measured the voltage drop before, only the resistor values I think. So I just whipped out my Fluke...

Total USB voltage 5.05V
Filco blue LEDs 2.55V, resistors 10kΩ, current 0.25mA
Filco red LEDs 1.97V, resistors 510Ω, current 6mA

I only did one measurement per color. The resistors are 5% I guess so it will vary a bit. Different colors have different efficiency I suppose.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Thu, 27 June 2013, 18:01:01
Thank you very much--this is helpful.  It actually means that my amber LEDs are pretty much within spec and are not getting overvolted at all.  It also explains why the UV LED did not turn on, as it required over 3V.  And finally, perhaps the amber LEDs were not made to be as bright as the Filco LEDs in general.
Title: Re: Swapping indicator LEDs
Post by: bpiphany on Fri, 28 June 2013, 06:48:34
Still, if there is no current the voltage across the LED is going to be 5V. As the current rises, the voltage across the resistor grows and decreases across the LED. This is going to reach an equilibrium at some point. There may be a lowest current where the LED will operate. I don't actually know, but I think it probably turns on only very dimly. If you have a volt meter you can check the voltage across the LED, and if it is lower than the USB voltage you know there is at least some current passing through.
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Tue, 02 July 2013, 21:19:46
Ok, based on a lot of different amber/yellow/orange LEDs I've tried, the important attribute to keep in mind is advertised brightness.  1000mcd+ for luminosity is going to be visible.  All the low numbers, in the hundreds or dozens of mcd is going to be very faint.  You'll see it "head on" but not at normal sitting angle really.  It'll be very faint.  Moreover, "water clear" (fully transparent) non-diffused is okay, but again, in recessed Filco casing, it will have terrible viewing angle.  So I recommend diffused LEDs of high brightness for wide-angle visibility.

I'm going with 1500mcd diffused amber/yellow lights, and they are by far not as bright as stock Filco blue LEDs.  I"m guessing the Filco ones are a few thousand mcds in brightness.
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Mon, 08 July 2013, 08:12:26
Quote from: Photoelectric on Tue, 02 July 2013, 21:19:46
I'm going with 1500mcd diffused amber/yellow lights, and they are by far not as bright as stock Filco blue LEDs.  I"m guessing the Filco ones are a few thousand mcds in brightness.

How much current are you putting through your chosen LED? 
How many mcd does that generate according to the LED datasheet?
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 08 July 2013, 08:15:33
I don't have a voltmeter / multimeter, as I saint earlier, hence why I made this thread.   Just have a look at the replies here.
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Mon, 08 July 2013, 12:22:20
What is the part number of the LED you used in the end?
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 08 July 2013, 12:40:20
This one, based on the color I liked and overall appearance:

http://www.mouser.com/ProductDetail/Kingbright/WP710A10SYC/?qs=sGAEpiMZZMtmwHDZQCdlqXHx%2fRptk0z22hBkOgd%252btPE%3d

If I were you, I'd order a bunch of different ones in the similar range and play with them to see what fits your color scheme / plan best.  I tried 10 different LED types before I settled on this one.  Some were too orange, some were too dim, etc.
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Mon, 08 July 2013, 13:47:16
So, your desired look was achieved with ~20mcd light output.
Others may want to target that same level as a starting point.

With this LED and the 10k resistor bpiphany measured, you're only
getting ~20mcd out of an LED easily capable of 1200mcd. That 10k
resistor only allows around 0.335mA through the LED, so you
needed a really efficient one to get your desired amount of light.

Plus, it is so efficient that your orange LED is green!
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 08 July 2013, 14:11:36
Huh?  It's not green at all... It's yellow-amber, as described.  It's not an orange LED.  It correctly looks exactly like this at 590nm:

(http://ledmuseum.candlepower.us/35/cpu-y3.gif)

I'm not sure how you're calculating such a tiny mcd value either, given the target brightness of 1500mcd...  20mcd is 1.3% of 1500mcd--surely it's not THAT dim!
Title: Re: Swapping indicator LEDs
Post by: Soarer on Mon, 08 July 2013, 14:52:50
Yeah, probably is, give or take a bit. Old-school bog standard red LEDs are about 20mcd (at 20mA) - about right for an indicator.

The calculation is simple to picture: big resistance -> small current -> low brightness.

For full brightness with that LED you'd want to give it 20mA, which would need a resistor of about 100 ohms (very roughly). But you wouldn't want to, it would be blinding!
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 08 July 2013, 15:13:19
For what it's worth, LEDs that I got from Mouser that were within an order of magnitude of 20mcd are all very dim on the Filco board.  The stock blue LED is truly blinding.  The 1500mcd LED I linked above is significantly brighter than 20-150mcd LEDs I also tried, but still not as bright as the stock Filco LED.  Considering that these LEDs vary in brightness amongst each other, given the same voltage and current, there is clearly intrinsic difference between them.  So you can't just take the current value and voltage and say that all LEDs of this size will be Xmcd in brightness.  Going by the intensity curve from the datasheet for the LED linked above, its intensity decreases linearly (page 3):

http://www.mouser.com/ds/2/216/WP710A10SYC-78718.pdf

To get to 20mcd, you'll need to give it VERY little current.  Target values are 2.5V forward voltage and 20mA current.
Title: Re: Swapping indicator LEDs
Post by: Soarer on Mon, 08 July 2013, 15:25:04
Well no, of course I'm not saying that! I'm saying that had you changed the resistor as well, you could get any of the others to be about the same brightness, i.e. 20mcd, since they were all capable of more than that. But with that large resistor you needed to use the one which would have 1500mcd @ 20mA. You're only giving it 0.25mA or so.

The intensity is fairly linear with current, but the forward voltage also depends on current, and isn't linear... so some guesswork is usually required to find the right resistance for a target brightness when using low currents.

In this case though, we're talking orders of magnitude, so such details are fairly irrelevant.

The clear intrinsic difference is their mcd rating, durr!
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Mon, 08 July 2013, 15:36:06
Well, my original point stands: the original Filco LEDs are still a LOT brighter, so they must be rated for thousands of MCDs.  Considering that they are blue too, when my replacement LEDs are amber.  I could not find equivalently bright LEDs from Mouser (not that I wanted to).
Title: Re: Swapping indicator LEDs
Post by: Soarer on Mon, 08 July 2013, 15:39:52
Yeah, blues are easy to make very bright, so they do! Probably 3000 to 5000 mcd, seems quite common.
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Mon, 08 July 2013, 15:45:41
Quote from: Photoelectric on Mon, 08 July 2013, 14:11:36
Huh?  It's not green at all... It's yellow-amber, as described.  It's not an orange LED. 

Sorry... a poor and FAILed attempt at environmentalist humor. You picked a very efficient LED.

As Soarer said, the datasheet shows a linear relationship
between current and light output. 1200mcd at 20ma... But you're
giving it very little current, so you get only a little light.

Title: Re: Swapping indicator LEDs
Post by: bpiphany on Tue, 09 July 2013, 11:08:43
Perceived intensity may also not be linear to actual light output. It may very well be that a doubling of the light flow is seen as much less.

You need to add a second function to the first graph of the forward current<->voltage drop figure in the datasheet. Call the V and I from the datasheet V_d and I_d. If V_d+V_r=5V and V_r=I_r×R then I_r=(5-V_d)/R where r and d is for resistor and LED respectively. I_r is of course equal to I_d the resulting current will be where they intersect.
Title: Re: Swapping indicator LEDs
Post by: bpiphany on Tue, 09 July 2013, 13:29:35
Like so. The lines are for different resistor values. I should probably have put some more values between 100 and 500, but I'm not going to do it again ;)

[attachimg=1]
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Tue, 09 July 2013, 13:34:55
Yikes, I just re-read your earlier post and realized just how huge of a resistor value is added for the blue LEDs.  I wonder why such a huge difference between red and blue.
Title: Re: Swapping indicator LEDs
Post by: Soarer on Tue, 09 July 2013, 15:28:58
Quote from: bpiphany on Thu, 27 June 2013, 16:00:10
Filco blue LEDs 2.55V, resistors 10kΩ, current 0.25mA
Filco red LEDs 1.97V, resistors 510Ω, current 60mA

Pretty sure that should be 6mA ;)
Title: Re: Swapping indicator LEDs
Post by: bpiphany on Wed, 10 July 2013, 04:43:29
Quote from: Soarer on Tue, 09 July 2013, 15:28:58
Pretty sure that should be 6mA ;)

Wasn't it always.... =P
Title: Re: Swapping indicator LEDs
Post by: korrelate on Wed, 04 September 2013, 13:42:42
Quote from: Photoelectric on Mon, 08 July 2013, 14:11:36
Huh?  It's not green at all... It's yellow-amber, as described.  It's not an orange LED.  It correctly looks exactly like this at 590nm:

Show Image
(http://ledmuseum.candlepower.us/35/cpu-y3.gif)


I'm not sure how you're calculating such a tiny mcd value either, given the target brightness of 1500mcd...  20mcd is 1.3% of 1500mcd--surely it's not THAT dim!

Hey Photo, what did you use to produce this plot of color by wavelength and intensity? I'm looking to do the same thing to my Tenkey Filco but I'm going from Red to Green and want to have an idea, before I order, what I'm getting.

Also, did you go with the 3mm leds and were they the right size? Any particular shape you had to buy (flange/ no flange), etc?

Cheers & Thanks for this thread!!
Title: Re: Swapping indicator LEDs
Post by: Photoelectric on Wed, 04 September 2013, 13:50:17
I did not make that plot--I just searched Google for color-wavelength intensity distributions / spectra, because when you look at LEDs on places like mouser.com, they are often designated by wavelength number, and you can't tell if a particular LED is more orange or more green.  Those charts help.

Here are some reference plots you can use for green LED light, to see if you're getting a more yellow-green or a colder green. 

(http://www.theledlight.com/images-tech/spectrum.jpg)

(http://ledmuseum.candlepower.us/24/l200cwg3.gif)

(Ignore the intensity and just look at the color that your reference wavelength corresponds to).

3mm (=T1) round LEDs are the correct size, yes.  Go for the highest luminosity you can find, or you'll end up with very dim LEDs.  Especially because the stock red LEDs probably have a fairly high value resistor.  I don't think it really matters whether the LEDs have a flat "base"--I taped mine to the right height (using scotch tape over the tops) after trying on the cover carefully, and then soldered them on at that height.  Then snipped off the loose ends.
Title: Re: Swapping indicator LEDs
Post by: korrelate on Thu, 05 September 2013, 08:36:53
Roger that and thanks for the info. I've got some homework to do. I've only dabbled in electronics a couple of times but I'm going to take bpiphany's meaures on the LED and resistor for the Filco Red LED and try to determine what an appropriate profile would be for a replacement Green. I'll post my progress as I make it. If I get a chance I'll try to add the series that bpiphany omitted from his chart (FC vs. FV for resistance btw 100 and 500).

Can someone confirm my understanding of "forward" as it relates to C an V. Take V for example, and let's consider FV of a (light emitting) diode. Is FV the voltage that's "coming out" of the diode? I.e. the voltage "into" the diode minus the drop associated with the diode?


Cheers,

K
Title: Re: Swapping indicator LEDs
Post by: bpiphany on Thu, 05 September 2013, 10:22:49
The forward voltage is the voltage drop across the diode. So the voltage on the lower end is equal to the voltage on the high side minus the forward voltage.

To my understanding there is a "gap" where the electrons lose F_V as they jump across. Each electron jump gives off exactly one photon. Using some familiar(?) equations and a voltage drop of 3.2V.

That is 387 nm (or something purple). There probably are some extra voltage losses in the component other than over the photon producing gap. This leads to a longer wavelength of the actual output light.

The light color depends on the voltage drop as above. The light intensity is proportional to the current flowing through the diode. Remember each electron gives rise to one photon. The voltage drop is more or less constant independent of the current (over the intended working range). The current can therefore be controlled by the series resistor. The voltage drop across the resistor is equal to the resistance times the current. The voltage drop across the resistor and diode adds up to the total applied voltage, usually 5V in keyboard cases.

google calculator (https://www.google.com/search?q=speed+of+light+÷+(1+electron+charge+×+3.2+volts+÷+Planck's+constant))
Title: Re: Swapping indicator LEDs
Post by: korrelate on Thu, 05 September 2013, 17:33:22
Bphiphany: now that looks like a real meal! I've got to sit down, let it sink in and digest all this info. Many thanks!
Title: Re: Swapping indicator LEDs
Post by: frogamic on Thu, 05 September 2013, 21:02:11
I switched the LEDs on my Filco from blue to green to match my Deathadder, I really wish they'd just put normal resistors on the main board, there's no shortage of space in that area. The greens are much brighter than the old blues, I'm thinking I should actually solder resistors directly onto one of the legs of each LED, but I can't really be bothered right now.
Title: Re: Swapping indicator LEDs
Post by: bpiphany on Thu, 05 September 2013, 23:53:50
You can always resort to the state-of-art black Sharpie solution =)
Title: Re: Swapping indicator LEDs
Post by: korrelate on Sun, 15 September 2013, 14:14:51
Quote from: bpiphany on Thu, 27 June 2013, 16:00:10
I actually don't remember if I measured the voltage drop before, only the resistor values I think. So I just whipped out my Fluke...

Total USB voltage 5.05V
Filco blue LEDs 2.55V, resistors 10kΩ, current 0.25mA
Filco red LEDs 1.97V, resistors 510Ω, current 6mA

I only did one measurement per color. The resistors are 5% I guess so it will vary a bit. Different colors have different efficiency I suppose.


Hey bpiphany,

I'm trying to derive the specs for the red leds in your example above. I'm using the fact that the sum of the drops has to equal the total V (I) input.
If I assume that input is 20mA @ 5.05V here's what I get for FV and FC:

FV:
Resistor 3.08V
LED 1.97V

FC:
Resistor .006A
LED .014A

And in my case, I'm going to replace the red LEDs in my Filco MJ2 (100% layout) with green less. So this means I need to find a green LED with FV around 2V and FC around 14mA.

Am I on the right track here?

Cheers,

K
Title: Re: Swapping indicator LEDs
Post by: OldDataHands on Sun, 15 September 2013, 17:22:12
Quote from: korrelate on Sun, 15 September 2013, 14:14:51
Am I on the right track here?

You've got the voltage split correct, but the same current flows through both the LED and the resistor.
bpiphany indicated that the LED is driven with 5.05v over a 510Ohms resistor.
Ohms law: I = E / R :applies like: I = (5.05v - 1.97v)/510Ohms ~= .006Amps
This 6mA current flows through both the resistor and the LED.

You'll need to pick a green LED, then substitute its forward voltage (instead of the 1.97v) into the above
equation to find out how much current will flow through it.

If for some reason you really wanted to drive the LED at 20mA (you don't though, it'll be too bright) then
you'll need to change the resistor to get the right mix.
Title: Re: Swapping indicator LEDs
Post by: korrelate on Tue, 17 September 2013, 14:45:32
Roger that ODH, thanks for the feedback.