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Topic: Custom 16x16 RGB grid, what pixels to get? (Read 1 time) previous topic - next topic

pepeu

May 01, 2015, 07:38 pm Last Edit: May 01, 2015, 10:36 pm by pepeu
Heya! I was thinking about making a 16x16 RGB LED matrix thingie to show animations and old school 8-bit graphics on it. Pretty much like http://www.tested.com/art/makers/455872-maker-project-rgb-led-animated-pixel-box/ with a custom frame to it as well. But I'm not sure of what pixels to get. Should I get 2 x https://www.adafruit.com/products/1507 and just cut them all up and place them with the spacing I want, or? Caveats, tricks, cheats, beeps and boops?

All inputs and tips are welcome!

CrossRoads

#1
May 01, 2015, 09:42 pm Last Edit: May 01, 2015, 09:42 pm by CrossRoads
You could use the Neopixel (WS2812B) but will need a lot of current as you will effectively have 16x16x3 LEDs in parallel being powered. At high brightness, 20mA, that's a lof of current.
A less power hungry solution would be a multiplexed display.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

pepeu

Yea, the strips are WS2812B ones. I'm planning on getting a 5v/10A power supply to drive them. Adding a MSGEQ7 and use it as a spectrum analyzer is also on the to-do list in my head. But hm, multiplexing would be a cool feature to the project. And, power saving too!

PaulRB

#3
May 01, 2015, 11:38 pm Last Edit: May 01, 2015, 11:40 pm by PaulRB
Yea, the strips are WS2812B ones. I'm planning on getting a 5v/10A power supply to drive them. Adding a MSGEQ7 and use it as a spectrum analyzer is also on the to-do list in my head. But hm, multiplexing would be a cool feature to the project. And, power saving too!
All multiplexing does is send current to one group of leds at a time, then the next group and so on, at high speed. This has the side effect of dimming the leds, and saving power, because each receives less current on average.

The effect is exactly the same as using a lower pwm duty cycle. For example if you use a 1/8 multiplex ratio and each led receives 16mA when it is switched on, it only gets 2mA on average, and its the average current that determines the brightness. This is equivalent to pwm with a 12.5% duty cycle or analogWrite(pin, 32);.

So, yes, ws2812B can use a lot of current, but they don't have to. If you only use low brighness/pwm settings, it will use exactly the same power and give exactly the same brightness as a multiplexed display. But it will be far simpler to build!

pepeu

I'm going to get a 10A power supply for it, so I should be covered either way.

I played around with some multiplexing on a small scale 8x8 led grid just to get a hang of it. Took some guides, hints and trial and errors, but got it working after all. Tried some variations with 2 x 74HC595 and then some with MAX7219.

My first goal here will just to get it up and running. Charlieplexing will have to be added in later. I'm expecting the frame building and separation of the leds from each other will take quite a lot of effort to get it just right.

PaulRB

Charlieplexing as well now!?!

Either you are confused about your project design, or I am. You do realise that when using ws2812b leds, you don't have any need or reason to do multiplexing or charlieplexing at all? In fact  if you tried multiplexing them, you would just get terrible flickering. You can't do charlieplexing with them in any way I can think of, but again, if you could, they would flicker.

So either use ws2812b leds without multiplexing or charlieplexing, or use ordinary leds with multiplexing or charlieplexing. The second way is a much harder project!

PaulRB

Have you seen these 8x8 ws2812b modules? 4 of those would make your project much easier.

pepeu

Ah, never mind. My bad there. First off, my nooby brain thought of multiplexing and charlieplexing as the exact same. And from what I could gather on the specs now they are too slow for it anyway. Ok, let's just leave it then. Thanks for ... igniting my brain a bit there. :O) For now I'm going with WS2812B LEDS. At some later point I might try for some other solution just to get a multi-/charlieplexed matrix with RGB LEDs.

Have you seen these 8x8 ws2812b modules? 4 of those would make your project much easier.
Thanks for the tip, but no, since I want to decide the spacing of them myself.

PaulRB


pepeu

Then these?
Yea, I was looking at something similar. Three 100-sheets and I'm set. Decent pricing. And no cutting needed. I saw some of the new quicker APA102 ones too, but... nah, that will have to be for another, future project.

Thanks for your help! :O)

bigalram

Pepeu,

Pardon me for jumping in. The 10-1000pcs WS2812B LED With Heatsink 5050 SMD RGB WS2811S that you're looking at are tiny, smaller than your fingernail. Exacting,detailed work.

Check these out: https://www.sparkfun.com/products/12986
These are very similar to 4 pin RGB LEDS that you are used to, yet still contain the WS2812 chip. Seemingly much simpler, less detailed work. But I'm old, and half-blind, and'll take easier, simpler every time.

pepeu

Ah, cool! But I think I'll go with three sheets. They seem easy enough for me and a lot less work than cutting strips for sure! These seem like a good deal: http://www.aliexpress.com/item/Newest-WS2812B-WS2811-WS2812-built-in-SMD-5050-Led-pixel-module-PCB-Addressable-RGB-modules-Strip/1897830725.html

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