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geekhack Projects => Making Stuff Together! => Topic started by: Turkishrambo on Tue, 12 November 2013, 23:09:08
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Im really bad with this kind of stuff.
I need resistors for my GON. Im using white leds for switches and SMD white led's for the middle.
Whats the ideal ohm for a PS2AVR 87 config.
I want them to be decently bright but not dim either.
Using these as middle leds = http://www.gonskeyboardworks.com/others/14-ledssmd-50-pcs.html
These for switches = http://www.ebay.com/itm/100pcs-2x3x4mm-White-Rectangle-Water-Clear-White-LED-Light-Lamp-Leds-124/261327529878?_trksid=p2047675.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D2665506975521885918%26pid%3D100011%26prg%3D1005%26rk%3D1%26rkt%3D5%26sd%3D251282205019%26
Thanks.
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Without any decent datasheet you are simply going to have to try with different resistances. I don't even see a current rating on any one of them. So it's impossible to say anything about the needed resistors at all...
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Without any decent datasheet you are simply going to have to try with different resistances. I don't even see a current rating on any one of them. So it's impossible to say anything about the needed resistors at all...
^-- this. Maybe you can contact the vendor to find out some info. You'll want forward voltage (i.e. 2.1v) and forward current (i.e. 10ma). Then you can calculate what resistance you'll need. Your source voltage (Vs) will be 5v, voltage drop through the LED would be 2.1 (Vled) and current through the LED would be 10 (Iled)... R = (Vs - Vled) / Iled
That said, since I'm unfamiliar with the GON, do you know if everything on the board is 5v, or is some of it 3.3v? You might need to crack out the multimeter to see what voltage is being supplied... (probabaly 5v, but you never know until you measure).
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Also, does the board have place for one resistor per LED (best) or one per group LED's (not as good). If it's one per group you need to do the calculations a bit differently.
The rectangular LED's at least list their forward voltage drop (3.2 to 3.4v), but not their current rating.
You can do a test with a variable resistor (potentiometer) if you have a multimeter. Take a 4.7k ohm log variable and set it to maximum resistance with one of the led's in series and connect it to the power on the board. Adjust until the brightness looks good to you (be careful not to burn it out, though). Then measure the resistance of the variable resistor and buy resistors with the closest value.
Repeat for the other LED type.
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I usually do what they did on the KMAC and just use 470ohm for everything
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I usually do what they did on the KMAC and just use 470ohm for everything
This is actually not a bad idea. Should be within scope of most LED's current handling and even if it isn't, LED's are pretty tough and can handle a fair amount of abuse before dying.
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I usually do what they did on the KMAC and just use 470ohm for everything
This is actually not a bad idea. Should be within scope of most LED's current handling and even if it isn't, LED's are pretty tough and can handle a fair amount of abuse before dying.
Would u say thats alot for what they would possibly require?
Thinking of buying a few different ohm values just to test which works best. IE 470,330 etc
Thanks!
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They sent out 50ohm with the clear LEDs in my LZ-GH. They are bright. I've also used 1k ohm on my Epsilon with my green LEDs and they work fine.
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I recently learned that the Poker 2's resistors are 560ohm. These are already on the pcb by default.
Hope this helps somewhat.
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Most Digital Volt Meters have a diode setting -- you can use this to measure the forward voltage. As for the current, you will have to experiment (even if you know the rated current) -- try to minimize the current used, since USB 2.0 is limited to 500mA max. on a host port. I recently got a few sample LED's from Max Keyboards (http://www.maxkeyboard.com/keyboard-parts/led-lights.html), the pink, white, and green all work with 2.2kOhm (ie. slightly over 1mA !!) and are bright as hell. The orange is darker in general but still works fine w/ 3-4mA. If you need more than that to get decent brightness I would look for better LED's.
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I think the multimeters measure the voltage at a given current. It tries to force a set current through the diode, say 2mA perhaps. The forward voltage will vary with the current, so that isn't the full story even if it helps getting closer to the characteristics of the diode.
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I have 1.2kOhm resistors installed by Alaric on my LZ-GH for red LEDs (2012 size). I was originally going to replace them with something like 800 Ohm for ~3V LEDs, but after testing, the LEDs I want to use are bright enough on the existing 1.2kOhm resistors (warm white and cyan, which are ~3.2V). I would say that my pink, blue, and white rectangular LEDs would be happier with lower resistance though, as they seem a little on the dim side, so I'd do ~700-800 Ohm for those in 2012 size. I think GON's board is probably similar enough to use the same for a guideline. Here's his keyboard store, and you can see that 2012 resistors are what he uses too:
http://www.gonskeyboardworks.com/11-others
820 Ohm is one of the choices, so that's what I'd probably get as a fits-all solution if you're going to get some 2x3x4mm LEDs from eBay.
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I have 1.2kOhm resistors installed by Alaric on my LZ-GH for red LEDs (2012 size). I was originally going to replace them with something like 800 Ohm for ~3V LEDs, but after testing, the LEDs I want to use are bright enough on the existing 1.2kOhm resistors (warm white and cyan, which are ~3.2V). I would say that my pink, blue, and white rectangular LEDs would be happier with lower resistance though, as they seem a little on the dim side, so I'd do ~700-800 Ohm for those in 2012 size. I think GON's board is probably similar enough to use the same for a guideline. Here's his keyboard store, and you can see that 2012 resistors are what he uses too:
http://www.gonskeyboardworks.com/11-others
820 Ohm is one of the choices, so that's what I'd probably get as a fits-all solution if you're going to get some 2x3x4mm LEDs from eBay.
Will go with that! Thanks :D
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Just keep in mind that different LEDs have different internal brightness properties. So like my purple 2x3x4mm LEDs from eBay were rated at something like 3000 mcd, and my cyan LEDs were listed as 600 mcd. However, the cyan LEDs are brighter than the pink LEDs on the same resistors, while requiring the same voltage range. So if you're going to mix LEDs, you may need to experiment. The difference shouldn't be too drastic but you'll have to see. Also, green LEDs, which are meant to be run at ~2-2.4V are the brightest of the lot, understandably, as the rest of my LEDs are 3-3.4V kinds. So if you're going to mix green/yellow/red/orange (~1.8-2.2V range) with cold colors like blue/pink/white/cyan (3-3.4V range), you may need to use different resistor values. But that's easy to test--just solder a few resistors, insert your LEDs without soldering them (may need to wiggle them around to get proper contact), turn on, and compare. Here's my comparison I did for myself
[attachimg=1]
All but the green LED on the left are 3-3.4V range. So green is the brightest. Cyan is brighter than magenta, though should be the other way around according to listed specs.
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I think the multimeters measure the voltage at a given current. It tries to force a set current through the diode, say 2mA perhaps. The forward voltage will vary with the current, so that isn't the full story even if it helps getting closer to the characteristics of the diode.
Just measured some numbers on a live circuit -- the biggest deviation I got was +0.15V on the voltage determined by a DVM (Fluke 85 II.) For resistor calculation the deviation can safely be ignored IMHO.
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The LEDs have a typical current and voltage rating. The voltage drop varies with the current though. Here is a couple of posts from another thread along with a voltage-current graph from a datasheet. Some LEDs require very little current, far below the typical rating.
http://geekhack.org/index.php?topic=44798.msg955118#msg955118
http://geekhack.org/index.php?topic=44798.msg943832#msg943832
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Square LEDs are a hit and miss. I built a ps2avr with 5 different LED colors, the green square ones I used were way too dim, even after using a very low resistor value. But to be fair, they were bought from China with no specs on them, so I expected this.
Photoelectric, where did you find cyan square ones?! I looked for a long time but only found round cyan, which wasn't even really cyan when I got them.
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Aliexpress. If you search for 2x3x4 cyan they should come up. Took a month to arrive. They are on the green side--I'd call them turquoise. Cyan is more blue than green.
The only ones I haven't been able to find that I want are rectangular 'warm white' and 'amber'. I see them on sites that don't ship to the U.S. :( Even contacted one major distributor, but he wanted $30 DHL shipping for a tiny packet with 100 LEDs.
P.S.: seems like flat top round are actually worse than regular T-1, because the flat top is wider at a certain height. I'd like to find normal rounded T-1s but without the bottom skirt part. I can file them off , which I've done for like 25 LEDs, but it takes time.
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Yeah rectangle ones are not perfect, and some rectangle ones are even larger than others even though they're all advertised as 2x3x4. When they're larger, it's hard to seat them into the switch perfectly straight.
Anyways, if you really want accurate brightness, trial and error is the only way to go. Advertised brightness (mcd) specs on mouser and digikey won't turn out to be what you expect. When I first bought them, I went by specs and turns out same color, same forward voltage, and same brightness turned out to have different brightness using the same resistor value. I never go by those mcd numbers anymore. Resistors and LEDs are cheap enough where you can just buy a bunch to experiment with.
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Oh I meant the cylindrical ones--they are called 'flat top' in eBay listings. Like the warm white one on my photo, all the way to the right. I haven't had any issues with 2x3x4 ones: all of mine are identical.