midix
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Looking for a bright RGB addressable LED strip

Sat Jan 10, 2015 7:15 pm

Hi all.

I'm looking for a bright RGB LED strip which can be easily attached and programmed from Raspberry Pi. I want to control color and brightness of each LED light separately.

I have done some investigation of available options but I haven't yet found the one I'm sure about.

As I understand, I would need addressable (also called digital) strips. Many tutorials online do not mention what kind of strip they are using and sometimes it takes reading half the article to understand that they are talking about non-addressable strip.

I have looked at Adafruit options and it seems they have two options - older NeoPixels and newer DotStars. Here is the article about their differences:
https://learn.adafruit.com/adafruit-dotstar-leds

As I understand, DotStars should be more universal, hassle-free and beginner-friendly, right?

The only complicated thing is this one:
For low-voltage microcontrollers and systems such as Raspberry Pi, a logic level shifter (e.g. 74AHCT125) is recommended for both the data and clock pins.
As I'm not good with soldering (wires - no problems, chips - better not), I'd like to have some ready level-shifting solution which can be just attached to RPi and the LED strip. Could you please recommend something?

So, I'm looking at these options:
https://www.adafruit.com/products/2238
https://www.adafruit.com/products/2240
https://www.adafruit.com/products/2329

but I'm in doubt that LED strips which are using 5V power might be not enough bright. I have not seen them in real life, so I'm not sure how bright they are. Is there any brighter RGB addressable LED RPi friendly solution? Maybe something 12V would work better, but then how do I attach it to RPi? I intend to use a computer PSU for a prototype, so I'd have good 12V for LED, but I'm not sure how to make the signal levels match the ones of RPi then.

Also, I'd like to have some light spreading screen which can be used with the strip because I want the light to look like wide belt with blurry vertical bands of light. Is there any simple plastic screens which can be used as light spreaders? Is there any tutorial to make such screen myself? I could not find any, maybe I don't know the right keywords (English is not my native language).

BTW, I'm from Europe, so I guess I'll have to look for the closest Adafruit distributor to minimize shipping cost. Or I could use some cheap chinese solution from DX.com, if there is anything worth looking at.

Thanks for any ideas.

BMS Doug
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Re: Looking for a bright RGB addressable LED strip

Sat Jan 10, 2015 9:25 pm

Have you seen this blog post on the raspberry pi main site? The wordclock is made using a strip of LCDs.

I don't know if the video helps you decide if they will be bright enough, hopefully it will help you decide. I think the linked ws2812 led is the same as the adafruit one.
Doug.
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simplesi
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Re: Looking for a bright RGB addressable LED strip

Sat Jan 10, 2015 11:14 pm

This is one of those things that doing something is better than talking about it.

You can plug a £5 small strip/ring of neopixels into a PI by just connecting up 3 wires and the njudge for yourself if they are bright enough

Simon
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midix
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Re: Looking for a bright RGB addressable LED strip

Sat Jan 10, 2015 11:46 pm

Thanks for the worldclock link, I haven't seen it yet.

Yes, I guess, I can buy a smaller strip or just some LEDs.

I'm just not sure about those controllers and which ones are more beginner friendly and stable with Pi.

For example. Adafruit NeoPixels say that they use WS2812S (older) or WS2812B (newer). No controller mentioned, and in description they say that NeoPixels might not be a good option for Raspberry Pi, quoting:
The protocol used is very very timing-specific and can only be controlled by microcontrollers with highly repeatable 100nS timing precision. We have example code for using with the Arduino Uno/Mega microcontroller at 8MHz and 16MHz, and with a little effort you can use with the Raspberry Pi
Well, I don't like "little effort", it would be better to have "no effort" :D As an alternative, Adafruit recommends LPD8806 strip (but the problem - their older models might have HL1606 chip instead, so this is again confusing). And then that DotStar which is their newest model and has APA102 chip.

But I have also seen other options on Amazon which say:
WS2812B Stripe with integrated WS2811 controller
http://www.amazon.de/St%C3%BCck-WS2812B ... B00KGGGEVC
I don't understand, how they mean it - how can the stripe be WS2812B if it has WS2811 controller and
if it is a better option than Adafruit NeoPixels which have WS2812B only? :?

And also this one which has only WS2811:
http://www.amazon.co.uk/WS2811-Pixels-d ... 00MYOCI9G/
(not a strip, but still pretty cheap option, this might work for me if RPi can connect to it fine).

Essentially, the question boils down to which LED strips and chips (or their combinations) are the most hassle-free to interface and work with on RPi: WS2811, WS2812B, WS2812B with WS2811 (as Amazon claims it), LPD8806 or APA102, and which would give me fast reaction and less noticeable PWM flickering? I want it to be work as music light or an ambience in a dark room, so it should cause as little eyestrain as possible.

Another confusing thing is that level shifting. In worldclock video he mentions that they didn't use it but still the strip works fine. But I guess it would be safer to pick some level shifter, I'm just not sure what kind I will need. I'll look here on the forums for it.

BMS Doug
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Re: Looking for a bright RGB addressable LED strip

Sun Jan 11, 2015 12:19 am

I'm sure Joan's PiGPIO will be able to handle the timing requirements (and the wordclock makers got it figured out, in a worst case scenario you could just steal their code and modify it to suit your application).

For a level shifter i think you would need a transistor or opto-isolator as you need to shift the pi's output voltage to within 0.7xVDD (value will depend on the operating voltage of the chip not the strip, a 12v strip might still only have 6v on the chip).

The wordclock guys didn't use a level shifter with their 5v strip, the spec says 0.7 x VDD which would leave them needing 3.5v while only supplying 3.3v it's possible that over time the strip might stop working but it will probably be ok. Try to have the first LED close to the pi to get the best possible signal at the first LED (the other LEDs won't matter as the signal cascades from LED to LED).
Last edited by BMS Doug on Sun Jan 11, 2015 10:48 pm, edited 1 time in total.
Doug.
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midix
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Re: Looking for a bright RGB addressable LED strip

Sun Jan 11, 2015 5:01 pm

Ok, after lots of searching, I found some forum posts which mention the following important information:
I've been told the WS2811 means a chip and WS2812(B) means the LED with the chip mounted inside the LED housing.
Now this makes sense why some web stores call it WS2812 with WS2811 controller. :D And this means that all of them might be not the best option (as Adafruit explains it), so I might have a better luck with APA102, if only they have good support for RPi, no matter of their strip connections.

Also, I found that APA104 is a different beast again - it is more similar to WS2811 with just one data pin versus APA102 which has two pins.

Is there anything special about Adafruit APA102 strips, or I can take any APA102 strip from e-bay and be sure that it will work fine with existing RPi libraries which were created by Adafruit for their APA102 strips? To be more specific, I'm looking at this one:
http://www.ebay.com/itm/APA102-30-48-60 ... 418e0054f5

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Re: Looking for a bright RGB addressable LED strip

Sun Jan 11, 2015 5:16 pm

I've used Neopixel rings (WS2812b) with the Propeller based RoboPi 3.3V output without any difficulties at all (power to the ring was 5V)
BMS Doug wrote:I'm sure Joan's PiGPIO will be able to handle the timing requirements (and the wordclock makers got it figured out, in a worst case scenario you could just steal their code and modify it to suit your application).

For a level shifter i think you would need a transistor or opto-isolator as you need to shift the pi's output voltage to within 0.7xVDD (value will depend on the operating voltage of the chip not the strip, a 12v strip might still only have 6v on the chip).

The wordclock guys didn't use a level shifter with their 5v strip, the spec says 0.7 x VDD which would leave them needing 3.5v while only supplying 3.3v it's possible that over time the strip might stop working but it will probably be ok. Try to have the first LED close to the pi to get the best possible signal at the first LED (the other LEDs won't matter as the signal cascades from LED to LED).
http://Mikronauts.com - home of EZasPi, RoboPi, Pi Rtc Dio and Pi Jumper @Mikronauts on Twitter
Advanced Robotics, I/O expansion and prototyping boards for the Raspberry Pi

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joan
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Re: Looking for a bright RGB addressable LED strip

Sun Jan 11, 2015 6:05 pm

I would like to point out that pigpio can not drive WS2812B (or similar) LEDs with waveforms.

These LEDs use a proprietary serial message format.

A chap did manage to drive a few of the WS2812B LEDs with pigpio and SPI but it was not reliable for more than a few LEDs.

For this sort of LED you'll need to use a solution such as that suggested by mikronauts or a software solution based on the Pi's PWM peripheral which was linked to on the Adafruit site.

midix
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Re: Looking for a bright RGB addressable LED strip

Tue Jan 13, 2015 7:31 pm

Thanks, joan, this was exactly what I was afraid of.

So I guess, I should take APA102 based LED strips because they have an internal PWM controller, thus they should be more stable with RPi, right?

BMS Doug
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Re: Looking for a bright RGB addressable LED strip

Wed Jan 14, 2015 12:24 pm

midix wrote:Thanks, joan, this was exactly what I was afraid of.

So I guess, I should take APA102 based LED strips because they have an internal PWM controller, thus they should be more stable with RPi, right?

If you have time enough to wait for a kickstarter to fund and deliver then I would recommend backing this kickstarter:
The great thing about Neopixels is they are not just for Christmas, you could decorate a room, bedroom or light up your car with them. Use them around your garden (waterproof ones recommended here) or even the office.

So why am I here again, well after siting down with pen and paper i couldnt really get the price down much lower than £8, but trying my hardest with juggling figures and amounts I soon realised that if i went for around 220 boards I could just scrape in at £6 with the next discount rate at 500 which could bring the cost down by another £1 per board. I dont like producing boards that cost lots, as with my ethics I aim to sell at pocket money rates and £6 has always been a pretty good level with all my previous boards.

The main cost as ever is the PCB taking up over half of the costs, we then have the chips in second place, postage and headers plus kickstarter fees which are 15-20% of project funding on average.

Ok what will you get? you will get a PCB board with extended header, the control chip as mentioned above and 5 header pins for connecting neopixels too and power. As you will see with my board its been resoldered a few times after breaking on travels to jams.

What will you need to go away and buy to make it work? Apart from the obvious of a Pi, soldering iron and solder, you will need to source your own power supply and own neopixels as its something i wont be able to get cheap as I will get hit with huge import and custom charges for ordering in huge amounts which would mean passing it on to yourselves thus why I am pointing you to where to find them.
TL-DR: neo-pixel controller board £6 (add your own LEDs).
Doug.
Building Management Systems Engineer.

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Grumpy Mike
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Re: Looking for a bright RGB addressable LED strip

Sun Jan 18, 2015 12:04 pm

joan wrote:I would like to point out that pigpio can not drive WS2812B (or similar) LEDs with waveforms.
A chap did manage to drive a few of the WS2812B LEDs with pigpio and SPI but it was not reliable for more than a few LEDs.
That makes no sense at all. The signals are regenerated on each WS2812b LED so if you can drive one you can drive any length of string of LEDs. What your "chap" probable did was run out of current on the 5V supply from his Raspberry Pi.

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Grumpy Mike
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Re: Looking for a bright RGB addressable LED strip

Sun Jan 18, 2015 12:42 pm

midix wrote:Hi all.
I have not seen them in real life, so I'm not sure how bright they are. Is there any brighter RGB addressable LED RPi friendly solution? Maybe something 12V would work better, but then how do I attach it to RPi? I intend to use a computer PSU for a prototype, so I'd have good 12V for LED, but I'm not sure how to make the signal levels match the ones of RPi then.
The voltage driving an LED does not have any effect on the brightness. Those 12V strips have resistors built in and have three LEDs in series, so you can never control them individually. What matters for the brightness is the current and this is the same whether it is derived form 12V or from 5V because the control on the strip limits the current to the LED to what it should be, which is 20mA.

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Re: Looking for a bright RGB addressable LED strip

Sun Jan 18, 2015 2:26 pm

Grumpy Mike wrote:
joan wrote:I would like to point out that pigpio can not drive WS2812B (or similar) LEDs with waveforms.
A chap did manage to drive a few of the WS2812B LEDs with pigpio and SPI but it was not reliable for more than a few LEDs.
That makes no sense at all. The signals are regenerated on each WS2812b LED so if you can drive one you can drive any length of string of LEDs. What your "chap" probable did was run out of current on the 5V supply from his Raspberry Pi.
Not so, each additional LED needs it's own instruction string. The shorter the LED chain the less instructions transmitted.

Each WS2812b removes the first set of instructions then retransmitted the rest.
Doug.
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joan
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Re: Looking for a bright RGB addressable LED strip

Sun Jan 18, 2015 2:58 pm

BMS Doug wrote:
Grumpy Mike wrote:
joan wrote:I would like to point out that pigpio can not drive WS2812B (or similar) LEDs with waveforms.
A chap did manage to drive a few of the WS2812B LEDs with pigpio and SPI but it was not reliable for more than a few LEDs.
That makes no sense at all. The signals are regenerated on each WS2812b LED so if you can drive one you can drive any length of string of LEDs. What your "chap" probable did was run out of current on the 5V supply from his Raspberry Pi.
Not so, each additional LED needs it's own instruction string. The shorter the LED chain the less instructions transmitted.

Each WS2812b removes the first set of instructions then retransmitted the rest.
Correct. If the complete message fits in the SPI FIFO (from memory 128 bytes) then it was OK. Otherwise there is a point where the FIFO needs to be refilled in a timely fashion and that could not be guaranteed as the software to refill the FIFO was subject to Linux scheduling.

These refill errors are rare but each one causes the LED chain to reset, a highly visible glitch (so I'm told, I don't have a LED strip myself).

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Re: Looking for a bright RGB addressable LED strip

Sun Jan 18, 2015 4:41 pm

You just don't know what you are talking about I am afraid.

The length of chain has nothing to do with the GPIO's ability to drive the chain.
If the complete message fits in the SPI FIFO (from memory 128 bytes) then it was OK.
No, the Neopixel library uses the DMA not the SPI.

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joan
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Re: Looking for a bright RGB addressable LED strip

Mon Jan 19, 2015 10:11 am

Grumpy Mike wrote:You just don't know what you are talking about I am afraid.
...
Yes we do. We are talking about the capabilities of the pigpio library not about the capabilities of the Pi's gpios. If you reread the posts that will be clear.

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Grumpy Mike
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Re: Looking for a bright RGB addressable LED strip

Fri Jan 30, 2015 7:23 pm

Get this one:-
https://github.com/tdicola/rpi_ws281x
I have driven 240 LEDs with this, then I ran out of LEDs.

Install with:-

Code: Select all

   wget https://github.com/tdicola/rpi_ws281x/raw/master/python/dist/rpi_ws281x-1.0.0-py2.7-linux-armv6l.egg
    sudo easy_install rpi_ws281x-1.0.0-py2.7-linux-armv6l.egg
No need for any hardware buffer, just feed it with the 3V3 PWM pin GPIO 18

caca
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Re: Looking for a bright RGB addressable LED strip

Tue Dec 15, 2015 11:19 am

I think
  • ws2812b led strip
is enough bright

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