So, I have another idea for a project - which involves some, maybe lots of LEDs, all of which I’d like to control independently by some kind of microcontroller - there’ll be ~ 150 of them, and I’d quite like them to be those pretty multicoloured ones too. Is this plausible, or sane?
LEDs and that
Lots of solutions. For example.
150 individually addresable RGB coloured leds on a serial bus.
or
Multiplexing rgb led’s but as you would be talking 3 colour led’s you would have the equivelent of 3x150 led’s in the matrix. With port extenders to give you the i/o pins.
Could get away with an arduino depending on how quick you want them to change or react.
Gordon
APA102 aka DotStar is the new kid in town… Individually addressable LEDs with slightly less stringent requirements for control.
Apple had LED window displays in (I think) 2013 that looked interesting. From what I could work out it was long thin horizontal PCBs that held the LEDs and carried data, supported by vertical maybe 3mm rod that also carried power. That many LEDs need a lot of power…
Thanks, both. The APA102 LEDs look really good, and would be pretty easy to work with arduino too…
Or RGB LED strips wired to a DMX controller.
Ive ordered some addresable led’s from the far east to put in the μMeet kit for people to try out.
Ive also ordered some more DHT22, temp and humidity sensors to put in the box.
Theyl take at least a week to arrive.
Gordon
150 led is easy I hope as I’m working towards a project with some of this tech.
A powered USB hub with a selection of teensy at the end and each with a Octows2811 board.
https://www.pjrc.com/teensy/td_libs_OctoWS2811.html
[http://hackaday.com/2013/02/25/building-huge-displays-with-led-strips/
https://github.com/FastLED/FastLED/wiki/Parallel-Output
this ones 512
and my fave
https://forum.pjrc.com/threads/23756-first-small-scale-test-of-our-160x80-Video-wall
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I should imagine powering 150 leds would be interesting.
Also thats 3x150 if theyre all rgb led’s.
Hmm, the datasheet isn’t all that clear for the APA102 about what the actual peak current draw is (I get ~ 27mA, which seems unlikely http://www.adafruit.com/datasheets/APA102.pdf). The Adafruit tutorial for Neopixels (https://learn.adafruit.com/adafruit-neopixel-uberguide/power) suggests allowing for 60mA @ 5V.
To run 150 elements, would therefore require a draw of about 9A…
I think its the same as for the Neopixels - which is 60mA at maximum - ie. full brightness on R G and B.
It’s normal to assume here you won’t have all the LEDs lit at full brightness at same time…
This is true, but I will be wanting all of them on with some kind of color. But never all white. I would guess that 9A draw is pessimistic, can probably get away with half that.
A cheap PC power supply will supply that sort of current without much bother. I think there are some in the Space?
We have some pretty old bench power supplies too. But no one has tried/tested them yet.
By which I mean: there’s no need to spec a power supply, you can experiment and decide later.
If the bench supplies in the Space don’t work then we need to make sure they’re on the shopping list.
That’s great, I’ll have a look at what power supplies are knocking about in the arch tonight.
If I don’t use neopixels as a strip, but instead wire them up in series, but with a complicated loom that fits my own purpose. Would this end badly? I suppose my question is: Would an unusual, and perhaps not consistent resistance between each pixel bork the data?
If driving LEDs from a voltage source, the resistance of the circuit defines the current and therefore the brightness. So you’d want to keep resistances as similar as possible? Or have I missed something on the loom setup?
There is a bench power supply on the list of stuff to buy, but honestly not much progress has happened with the GLA spending recently, we need to get on that, but we’ve been focusing on the space. Would be good to get on that.
I read up on these led’s a bit last night.
I thought they were individually addressable but they arnt.
It seems you string them together in rows. Say 10 in a row and you want the 7th led to change colour.
Each led unit passes the command on to the next till it gets to the 7th led and carries out the command.
So they just count up till they reach that led.
So no distinct id like with the DHT22 temp sensors on I2C.
So you cant have a grid and tell a particular led to react.
You have to have them all strung together in a way that you can calculate which is the nth led.
In some ways thats easier then keeping a hash of all your led addresses but in other ways a bit clumsier.
Have a look at the Adafruit article:
https://learn.adafruit.com/adafruit-neopixel-uberguide/overview