Author Topic: A weird and wonderful RGB LED experience  (Read 2099 times)

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Offline TriodeTiger

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A weird and wonderful RGB LED experience
« on: February 13, 2013, 10:10:30 am »
I felt for some reason to share this with someone.

I had purchased some veroboard and never made anything with it for a year, so I wanted to show off a simple RGB LED fader (I got the common cathode LED with an Arduino kit) with button input and AVR.

So - I hooked up the LED and tested it. It was bright with a 10k resistor at 5V so I removed the ground to the breadboard as it was hurting my eyes (coming from an Arduino with USB, so common with earth) and put in next the buttons. I put in a wire from button to ground and the LED lit up - huh?

It seemed a little hit and miss - I wondered how on earth ground can be found through a button (which was d/c when not pressed) or if somehow it was fooling me and had a path through the button somehow, a 10k pullup to an output.

Something clicked in my head and I discovered I was touching the exposed leads of the wire, it had nothing to do with the button.

In the full blue, I measured, 1.4-4uA was enough to light up the tip of my finger with a desk lamp as background light. Red was just visible, green a little brighter than red, but 1/3 of blue still. I did this before with 36V or so from 9V batteries and a red LED to show people I really can power an LED through me and earth - but it was hardly visible.

Are RGB LEDs super super high efficient? It's not even clear, it is diffused. That blue is just insanely bright before  it reaches 200uA! Can I make a blue/green flashlight that lasts seemingly forever? I am completely baffled why it is like this, and more so happy I knew to test "Lets take one foot off the ground and see if the brightness halves..."

It is 2am so I am excited by random things - but discovery is what makes electronics fun.

TriodeTiger.
« Last Edit: February 13, 2013, 10:25:40 am by TriodeTiger »
"Yes, I have deliberately traded off robustness for the sake of having knobs." - Dave Jones.
 

Offline Psi

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Re: A weird and wonderful RGB LED experience
« Reply #1 on: February 13, 2013, 10:21:51 am »
Yeah, it doesn't take much current before you get light. 

Red/Orange are the most efficient.
Lots of research is going into getting white leds more efficient at the moment.

Interestingly, if you pulse leds for some reason (pwm etc.), you can even get them to produce a little light with one pin connected and the other pin floating in air.
Happens if the switching frequency matches up with the length of your wiring and it acts like a transmitter, you get a small current through the led into the air.
« Last Edit: February 13, 2013, 10:24:59 am by Psi »
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Offline houdini

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Re: A weird and wonderful RGB LED experience
« Reply #2 on: February 13, 2013, 10:44:12 am »
i have had the green ones light up while soldering them with one side in the air and the other on the iron.
 

Offline Flávio V

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Re: A weird and wonderful RGB LED experience
« Reply #3 on: February 13, 2013, 10:53:18 am »
Some of my power LEDs also light up a bit when i touch the wires(6.6V,700mA LEDs, create a light of near 5V)
 

Offline Psi

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Re: A weird and wonderful RGB LED experience
« Reply #4 on: February 13, 2013, 11:44:49 am »
i have had the green ones light up while soldering them with one side in the air and the other on the iron.

I wonder if that's 50Hz earth hum radiating from the iron or a thermoelectric effect from the heat.
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