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Author Topic: What LED to use for backligting ?  (Read 1476 times)

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Offline DonnyD

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  • Posts: 89
What LED to use for backligting ?
« on: Tue, 27 February 2018, 10:10:13 »
Should i look for some specific LEDs or just make sure i pair them with correct resistor and thats it ? What you used ? Just to clear things up, LEDs wiring must be COMPLETELY seperate from switch wiring right ? Just choose one of PWM pins for Input and ground ?
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Offline senso

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  • Location: Portugal
Re: What LED to use for backligting ?
« Reply #1 on: Tue, 27 February 2018, 11:00:06 »
And a transistor/MOSFET, because the Teensy can't supply current to all the leds.

Just size the resistor properly (Vdd-Vdrop)/0.010 will get you in the correct ball park.

Given that its USB an you use a transistor, Vdd will be 5v, Vdrop depends on the color of the led, and 0.010 means 10mA, thats plenty to get blinding levels of light from decent leds/made after 2010.

For leds, choose one colour, order 20 or more, they have polarity, so respect that when wiring them, and put one resistor per led.
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Offline DonnyD

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  • Posts: 89
Re: What LED to use for backligting ?
« Reply #2 on: Tue, 27 February 2018, 11:38:40 »
Got it !! I think were is plenty of schematics of LEDs with transistors, so i should be good there :) Thanks !!
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Offline Findecanor

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  • Location: Koriko
Re: What LED to use for backligting ?
« Reply #3 on: Tue, 27 February 2018, 12:18:22 »
USB is not rated to supply current to all the LEDs of a full-size keyboard. Backlighting is usually done with a separate driver chip which lights up a subset of the LEDs at a time. Because it is done really fast and modern LEDs are really bright, it will not look dim or flickering.
It could also be done with pins, but instead of PWM you would have to flicker the LEDs in software .. and your µcontroller would also need to have enough free pins.
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Offline DonnyD

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Re: What LED to use for backligting ?
« Reply #4 on: Tue, 27 February 2018, 12:18:45 »
What about these LEDs ? (https://www.amazon.com/gp/aw/d/B017TR9U8E/ref=mp_s_a_1_2?ie=UTF8&qid=1519754863&sr=8-2&pi=AC_SX236_SY340_FMwebp_QL65&keywords=1.8mm+LED&dpPl=1&dpID=31olSwdis8L&ref=plSrch) Size seems good. What about resistors recommended in the table for different voltages ? Should i trust it ?
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Offline DonnyD

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  • Posts: 89
Re: What LED to use for backligting ?
« Reply #5 on: Tue, 27 February 2018, 13:43:50 »
Quote from: Findecanor on Tue, 27 February 2018, 12:18:22
USB is not rated to supply current to all the LEDs of a full-size keyboard. Backlighting is usually done with a separate driver chip which lights up a subset of the LEDs at a time. Because it is done really fast and modern LEDs are really bright, it will not look dim or flickering.
It could also be done with pins, but instead of PWM you would have to flicker the LEDs in software .. and your µcontroller would also need to have enough free pins.

What about this post and both guys did 60% keyboards with that method. I am also planning 60-70%, so in theory it should be good.
https://geekhack.org/index.php?topic=94258.0
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