Power use of LEDs - some observations

The more technical aspects of Spirit, and carry-over discussion from Kickstarter updates.
gpvillamil
Posts: 75
Joined: Fri Jan 26, 2018 5:03 pm

Power use of LEDs - some observations

Postby gpvillamil » Mon Feb 12, 2018 1:58 am

I wrote a simple Rainbow Chase routine (attached), and tried it with different brightness values (max for rgb value), checking the current reading.

I find that the perceived brightness doesn't really increase that much past 50, but a lot of NeoPixel demo code does crank the values up to 255!

So it makes sense to put in a mapping/scaling function to adjust the brightness overall, you can save a lot of power.

Code: Select all

Brightness   Current
5      366
25      380
50      427
75      468
100      495
125      533
150      591
Attachments
Spirit_RainbowChase.zip
(54.08 KiB) Downloaded 29 times

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esba1ley
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Joined: Sun Jan 01, 2017 2:15 am
Location: Pasadena, CA
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Re: Power use of LEDs - some observations

Postby esba1ley » Mon Feb 12, 2018 2:02 am

Very astute observation. For power consumption purposes, capping the values of the NeoPixels to 127 is a really good idea. I'm not sure if it quite cuts power consumption in half... but it gets close. There may be some color shifting, though, because our eyes are more sensitive to some colors (greens and yellows, in particular). At some point if we REALLY want to get anal about this, we should do some sort of perception/calibration on only using half of the range... and we may want to cap reds and blues at a higher number than the greens, since our eyes are more sensitive to the green hues.
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Erik S. Bailey
Entry, Descent, and Landing Aerospace Engineer
Maker, and Musician
SpiritRover Kickstarter Backer #460

gpvillamil
Posts: 75
Joined: Fri Jan 26, 2018 5:03 pm

Re: Power use of LEDs - some observations

Postby gpvillamil » Mon Feb 12, 2018 2:31 am

I’m thinking of modifying SetPixelRGB to map incoming values to a range set by a constant somewhere, so that you can manage overall brightness for all sketches in one place.

Good point about calibrating the color channels to different values, though the rainbow chase does look plenty vibrant!


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