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Calibrate the LED colour?

asked 2015-01-29 09:13:19 +0300

pichlo gravatar image

updated 2015-01-29 12:59:00 +0300

chemist gravatar image

Is there any way to calibrate the LED colours? Mine are quite a bit off. White is actually pink, yellow is somewhere between yellow and green... Are they all like that or just me?

Please note that I am aware of editing the LED patterns in the MCE config file. My question is if there is a possibility to calibrate the colour at a more fundamental level, so e.g. even the CSD tool lights up white when it says white.

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A bit more investigation. Sorry, should have done that first, before posting.

The colour changes very slightly depending on the viewing angle and, when looking from the top at about 45° angle, I can actually see all the component colours. It looks like the individual components are not close enough together to blend.

With good blending, the white is still a bit pink (a colleague calls it lilac) but I take it back about the yellow. It looks orange-ish when viewed head-on (about 50° hue in this chart), only going into green from certain angles.

Of course, nothing can be done about the blending but, unless @juiceme is right and there is just one bit per colour, something might be doable about the components. Which, in my case, just means toning down the red a bit.

pichlo ( 2015-01-29 15:03:42 +0300 )edit

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answered 2015-01-29 12:56:51 +0300

Keeper-of-the-Keys gravatar image

Pink is B+r, Yellow is R+G, but if it's closer to Green r+G what you describe sounds like the red part of the RGB LED is not functioning properly/degraded...

To establish this properly I would suggest you make it flash only in primary colors (R,G,B [amber also?]) to make sure all individual components are working and putting out similar amounts of light... (if Red works but is only 10% as bright as Green and Blue that will skew all colors).

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Actually, R+B would make purple. Pink is R+g+b, i.e. white with a red bias. That's what confuses me: pinkish white points to a red bias but grenish yellow indicates a green bias.

Primary colours look OK in CSD. They all look a bit dim to me, I cannot honestly say that either of them is dimmer than any other.

pichlo ( 2015-01-29 13:11:12 +0300 )edit

I wonder how the device drives the RGB led component;

If there's just a current-limiting resistor and a FET for each colour, driven by 3 GPIO pins you cannot really "calibrate" it except by changing the SDM resistors.

If there is a real DAC driving each component, even some poor 4-bit-resolution sample/hold thingy, then you can change the colours prety much at will.

juiceme ( 2015-01-29 13:24:28 +0300 )edit

LED colours are determined by the type of semiconductor used, so you don't have much of a chance to calibrate them.

Giacomo Di Giacomo ( 2015-01-29 14:03:20 +0300 )edit
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@Giacomo Di Giacomo, that is a vague answer at best :)

"Type of semiconductor" well yeah sure the die and casing affect the emitted base colour but there's more than one way of getting the apparent colour to be what you want; for example controlling the forward current thru the individual LED's or better, applying a PWM signal to the LED's...

juiceme ( 2015-01-29 14:11:57 +0300 )edit

Of course you could think of doing a great part of the RGB spectrum if you can drive each LED with a different current, but I bet that each colour has a simple on-off switch. You could use PWM but you need a real-time task to precisely set the switching times, consuming a fair amout of CPU just to adjust the LED colour.

Giacomo Di Giacomo ( 2015-01-29 16:21:30 +0300 )edit
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Asked: 2015-01-29 09:13:19 +0300

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Last updated: Jan 29 '15