Driving WS281x RGB LEDs from an nRF51822

RE: Driving WS281x RGB LEDs from an nRF51822

Chris Bick — Thu, 02 Jul 2015 11:48:05 GMT

If you're looking to use the RedBear nRF51822 or their Nano device take a look at these posts for a solution.

github.com/.../1

redbearlab.zendesk.com/.../73654999-BLE-Nano-with-Neopixel-WS2812-mbed

RE: Driving WS281x RGB LEDs from an nRF51822

Eric Salem — Mon, 25 Nov 2013 22:55:50 GMT

See:

devzone.nordicsemi.com/index.php/lava-ws2812-b-neopixel-library

RE: Driving WS281x RGB LEDs from an nRF51822

Alex Shepherd — Thu, 07 Nov 2013 03:15:28 GMT

Hi Eric,

Any update on releasing the WS281x source code?

Alex

RE: Driving WS281x RGB LEDs from an nRF51822

Eric Salem — Wed, 30 Oct 2013 23:25:31 GMT

I don't have the final say on what happens to the code I write, but I believe our intentions are to release the c library for the WS281x on Github after more review of today's code changes. This would most likely happen within the next several days.

I will message both of you with more details later.

RE: Driving WS281x RGB LEDs from an nRF51822

Marc Nicholas — Wed, 30 Oct 2013 22:20:44 GMT

Are you able to share the code? A little late for Halloween this year, but there's always next year ;)

-m

RE: Driving WS281x RGB LEDs from an nRF51822

Alex Shepherd — Wed, 30 Oct 2013 20:21:41 GMT

Excellent - that's encouraging. The Nordic Tech guys confirmed that this approach should work well and your observations so far agree with this, which is good.

Alex

RE: Driving WS281x RGB LEDs from an nRF51822

Eric Salem — Wed, 30 Oct 2013 17:24:50 GMT

Great news! Thanks to your information about the Radio Events, info in the S110 doc, and the ble_radio_notification.c file I was able to successfully run my WS2812 driver library during the Radio quiet time. So far it has been working flawlessly!

Take a look at the heart rate sensor app to see how ble_radio_notification is implemented.

Thanks for the help Alex.

RE: Driving WS281x RGB LEDs from an nRF51822

Alex Shepherd — Wed, 30 Oct 2013 02:45:03 GMT

There is some discussion about this in Section 9 "Radio Notification" in the S110_SoftDevice_Specification v1.1.pdf document here: https://www.nordicsemi.com/eng/content/download/13238/213065/file/S110_SoftDevice_Specification%20v1.1.pdf

However I've not seen any examples of registering and handling the notifications. I'll lodge a support request.

My thoughts were to register a nACTIVE handler and then do my WS281x operation immediately after the nACTIVE notification as the BLE Stack should be quiet for a few ms after that notification - I'm hoping... ;)

Alex

RE: Driving WS281x RGB LEDs from an nRF51822

Eric Salem — Tue, 29 Oct 2013 18:08:30 GMT

I wrote the library in C, but the timed outputs uses inline assembly calls. I have continued testing this library because I felt I hadn't thoroughly tested it with BLE. I have found that indeed the softdevice interrupts cause an issue with the specific LED timing. Since, I have spent bits of time here and there looking for alternatives. I have been preparing a timer+gpiote program, but do not have my oscilloscope today to test it.

You mentioned below about Radio Notification windows. Do you have a link to the documentation on this or is there an example program that shows this functionality working?

RE: Driving WS281x RGB LEDs from an nRF51822

Alex Shepherd — Sun, 27 Oct 2013 08:44:17 GMT

Did you code it in C or Assembler?

RE: Driving WS281x RGB LEDs from an nRF51822

Alex Shepherd — Thu, 24 Oct 2013 21:25:17 GMT

Hi John, thanks for the feedback and directing my attention to the PWM + SD example. That looks to do most of what I want so hopefully I can tweak it to work for me.

Regards

Alex Shepherd

RE: Driving WS281x RGB LEDs from an nRF51822

John Kelley — Thu, 24 Oct 2013 13:25:23 GMT

It should be doable with Timer Compare regs + GPIOTE, look at the PWM sample code here on devzone for something to model it after so you don't need to do any polling. I would take the approach of using PPI to drive GPIOTE off one Timer Compare reg and use another Compare with the same CC value to setup the next bit for transmission.

Also, there is some neat but mostly inapplicable code (as far as nRF51822 is concerned) for driving WS2811s at github.com/.../

RE: Driving WS281x RGB LEDs from an nRF51822

Alex Shepherd — Wed, 23 Oct 2013 21:20:33 GMT

Hi Eric, Thanks for the feedback and good to know that it is possible.

The response from the Nordic Tech Support guys suggests that there is up to 7.5ms periods of time where there is no interrupt activity going on and that by using the "Radio Notifications" facility provided by the SoftDevice I should be able to figure out a "quiet time" to bit-bash the WS281x waveform. I need to drive about 60 nodes so that will take 60 x 25us = 1.5ms to clock out.

I'm thinking of using the Timer and Compare Registers + GPIOTE capability and poll the Timer state in a tight loop to adjust the ON -> OFF transition time to do the O or 1 bit encoding.

Alex

RE: Driving WS281x RGB LEDs from an nRF51822

Bastiaan — Wed, 23 Oct 2013 21:09:28 GMT

Ran a quick and simple test using the UART ble program to turn on a new LED at red for each serial packet collected and to turn off all LEDs on a write from the phone to the characteristic. Seems to run regardless of the softdevice running.

I have read into that makeshift SPI setup and seen the Teensy library, but again decided to implement my own NOP based library.

Sorry that I am not capable of sharing the code at this time.

RE: Driving WS281x RGB LEDs from an nRF51822

Guest — Wed, 23 Oct 2013 21:09:28 GMT

I have read into that makeshift SPI setup and seen the Teensy library, but again decided to implement my own NOP based library.

Sorry that I am not capable of sharing the code at this time.

RE: Driving WS281x RGB LEDs from an nRF51822

Eric Salem — Wed, 23 Oct 2013 20:46:34 GMT

I have implemented a library specifically for controlling these WS281x's using NOP calls timed to work. However, I have not tested it with the softdevice enabled and have only tried up to 4 parallel strips of 10 LED's each.

Will report back after testing with softdevice.

RE: Driving WS281x RGB LEDs from an nRF51822

Alex Shepherd — Wed, 23 Oct 2013 11:17:18 GMT

Yeah, I've looked at this for hours and the SPI only has a fixed selection of bit rates and the BLE SoftDevice adds too much interrupt latency to be able to get around and refresh Timer Compare regs in time.

So I think I'll have to add an additional CPU (AVR ATTiny85 probably) to drive these LEDs.

Alex

RE: Driving WS281x RGB LEDs from an nRF51822

Marc Nicholas — Wed, 23 Oct 2013 02:54:05 GMT

From what I recall, this controller is like a big shift register and you shift you last pixel out of the MCU into the first physical pixel which shifts it into the next one etc. etc.

I seem to recall timing issues and that you might have to constantly refresh the data stream?

Just thinking out loud: I wonder if PPI could help out here?

-m

RE: Driving WS281x RGB LEDs from an nRF51822

Ling LI — Tue, 22 Oct 2013 14:34:10 GMT

Yeah the EasyDMA is for the RADIO block, not accessable from user code.

I have no experience with this serial protocol (of unnecessarily high speed and weired custom timing). I guess the SPI solution you mentioned might be a suitable choice for nRF51. Concerning CPU overhead, let's hope the controller doesn't need constant control signal under stable conditions i.e., having internal latch/memory to keep the state. Otherwiese it's too bad; you may need a small AVR dedicated to this uninteresting, busy task.