I want to run the values I calculated by people here to make sure they make sense.
all keyboards should work fine with 1500 ohm resistors
Example red LED Vf 1.5V
Example blue LED Vf 3.2V
The entire matrix is to be kept under 300 mA and 1500 mW to leave 200 mA or 1000 mW for the controller (just a guess)
Resistor value (1500 ohm)
Compatible PCBs (110%, TKL, 75%, 660%)
Red LED current (2.5 mA)
Blue LED current (1.3 mA)
Red total power (1417.5 mW) for 110%
Resistor value (1200 Ohm)
Compatible PCBs (TKL, 75%, 60%)
Red LED current (3 mA)
Blue LED Current (1.5 mA)
Red total power (1331 mW) for 80%
Resistor Value (1000 Ohm)
Compatible PCBs (75%, 60%)
Red LED current (3.6 mA)
Blue LED Current (2 mA)
Red total power (1377 mW) for 75%
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Note, the above assumes the controller will need 200 mA (or 1000 mW) to work. This is just a guess.
Alaricljs taught me to aim for 3.0mA for LEDs and to never exceed 3.4mA to be safe. He gave me this handy link to make the calculations a breeze.
www.ledcalc.com
My hope is that this will help some people out who want to customize these PCBs or get into building custom backlit keyboards who have little to no experience in electronics. I used this for my LZGH.
The link will require you to fill in the following fields:
- Supply voltage = 5v (? See Note below)
- Voltage drop across = Each LED has a foreword voltage range that you can find in the item description on eBay etc. Use the lower end of the range to start with.
- Desired current = 3.0mA - 3.4mA
Number of LEDs connected = 1 (Since they are all fed individually)
When you hit calculate it will provide you with the nearest higher rated resistor. This is what you will need to buy. It will also show you the circuits total current consumption which should be close to what you entered as your desired current. (3.0mA - 3.4mA) This is for bright LEDs within a safe operating range. 3.4mA being brighter than 3.0mA of course.
NOTE: One thing I don't know is if all keyboards provide the same supply voltage. My LZGH was 5v. Are they all different? Can anyone answer this for me?
Anyway, playing around with this LED calculator should give you specific resistor values for all your keyboard building needs!
I hope this isn't derailing this thread too much. It is relevant after all.
I think you misunderstand the issue, sir. Alaric knows his stuff, but he was quoting safe values for an 87 key keyboard or smaller. If you run 108 LED's to 3.4 mA (even 3 mA) you will draw 324 mA just from that. Now it might work on a fullsize keyboard, but it only leaves 150 mA or so for the controller. As I said, I dont know what sort of current the controller will need, so I wanted to leave it at a safe 200 mA +
As far as LED calculators, of the 8 or so I've tried, I prefer linear's led wizard (
http://led.linear1.org/led.wiz ) for simple calculations like this one (ledcalc is not bad, just well suited to other sorts of led arrays. TG3 does a similar thing on the BL82, by stringing their led's into strings of two with a resistor)
Almost all modern LED's can operate safely at a much higher current than 3.4 mA. As long as you keep it under 10 mA you will most likely be safe and not burn the LED out (many are rated for 18 mA or more).
As far as supply voltage, I've yet to encounter a keyboard that doesn't use 5V, though I only have so many keyboards with LEDs. 5V is a good value, as it's readily available from USB / PS/2 and it's low enough that small resistance values are needed for current limiting.
I was able to find the following on winkeyless's page on the A87uEX
1. 키의 수가 많아졌으므로 Full LED를 PS/2에 연결하여 사용할 경우 텐키리스의 경우보다 저항값을 높혀주는 것이 안전 할 것으로 생각합니다.
하얀색/보라색 : 820 ->약1K
빨간색/노란색 : 1.3K -> 약1.6K
파란색/초록색 : 900 -> 약1.1K
1. The greater the number of keys Full LED jyeoteumeuro the PS / 2 when connected to the tenki nophyeo resistance values than in the case of leases that are thought to be safe.
White / Purple: 820 -> approximately 1K
Red / yellow: 1.3K -> approximately 1.6K
Blue / Green: 900 -> approximately 1.1K
From:
http://winkeyless.kr/80If a GH'er more knowledgeable in Korean than google translate would like to contribute a better translation, it would help understanding. I notice that his value for red (1.3k-1.6k) is similar to my estimate of 1500
For a 1.5v LED, a resistor of 1.3K will result in 2.693 mA through each diode. Now looking at the blog, I see 111 key (matrix tenkey) and 108 key layouts. Taking the 111 key as a "safe" example, that will result in almost exactly 300 mA taken by the LED array (leaving 200 mA for the controller)
It also looks like you can wire up the numlock key on the tenkey separately (as a true numlock key) or as just another LED in the array, though it may require a jumper.
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So I thought A87 boards were not assembled but with the MCU installed. I am just fine soldering the rest of the components myself. Are we getting everything soldered (even the LEDs) Maybe it's better to not have the LED resistors soldered, or maybe instead to produce a few different boards for people with different LED configurations. 1500 ohms should work for all LEDs regardless, but if I want mine to be as bright as possible with white or blue LEDs I will need to desolder some resistors and replace with lower value ones.
Finally: sprit you're awesome! Thanks for all the excellent work you're doing to get this group'buy to happen! I'll do what I can to support you.
