Using Tessel Servo module to control Adafruit NeoPixels

[andy_mcdonald]

Hi there,

I've just purchased a bunch of individual NeoPixels from Adafruit and was looking for some help to get them running via the servo module. Seems you guys have built a custom firmware version to do just that. Any documentation or tips would be greatly appreciated.

For what it's worth, I also purchased a couple of these 16-channel PWM drivers - they are similar to the servo module but are chainable. I was thinking of hooking them up to the SDA and SCL pins on the GPIO bank (similar to how it is done here) but I'm not sure whether that would be making things more complex than necessary. Any thoughts?

Finally, any idea how many NeoPixels I can chain together from one set of 3 pins? To be fair, that is perhaps something I should ask in the Adafruit forums.

Ultimately, I reckon driving a lot of LEDs is a pretty popular use case for the Tessel and the NeoPixels seem to have a lot of great features so I'm sure being able to get them to play nice together would help a lot of people. Once I can get them connected properly, I plan on building my own library which I'd be happy to share.

Cheers... Andy

[jon]

Hey Andy!

Thanks for getting in touch! You're in for a treat - the Neopixels are a blast to use. I'm actually just finishing up a blog post about how we implemented support for them.

With regards to the PWM drivers, you won't actually be able to use them to drive the Neopixels. Neopixels have their own protocol which is more closely related to PWM, if you're familiar with that. To get started with Neopixels on Tessel, check out the neopixels library I built. To install, you'll need to download and flash the custom firmware I link to on that page, then npm install neopixels.

The primary limitations when you're chaining together neopixels are (in order of severity):

• Power: Neopixels are super power hungry and you'll need a separate power supply. Check out Adafruit's advice

• Frame Rate: The more Neopixels you have, the longer it takes to update the entire strip. As an example, I worked with 1260 Neopixels in a single strand and got a refresh rate of 26 fps with Tessel. Here is what 1260 Neopixels at 26 fps looks like. And Adafruit's guide can help with those calculations.

• Memory: Tessel has 32MB of RAM. You'll be hard pressed to create an animation that's larger than that but I'm sure you could do it.

Hopefully that's enough info to help you get started!

As a side note about the PWM drivers, we basically forked a copy of Adafruit's design so you can actually use our Servo library to use it to drive servos, leds, etc. Just npm install servo-pca9685 to get started.

-Jon

[andy_mcdonald]

Hey @jon!

Thanks so much for the quick response. I'll give all this a try but it looks fantastic - very excited!

Shame I cannot use the PWM drivers (I had a feeling they wouldn't be compatible when I bought them). I've got a 5V 10A power supply so that shouldn't be a problem.

With regards to the library, my knowledge of C is pretty basic but I'd be very keen to help out with some more high level JS animation features.

I'll let you know if I run into any issues but once again, thanks for the help.

Andy

[kevin]

NeoPixels have the control electronics built-in, so they take digitial commands instead of PWM'ing them directly. PWM drivers would be what you want if you were driving lots of individual LEDs without built-in controllers, but that chip can't generate the more complex waveforms that encode the commands for NeoPixels.

[andy_mcdonald]

Adafruit's advice

Thanks @kevin - that makes sense.

Forgive the noob question (my electronics knowledge is a bit rusty)... in the readme for the neopixel library @jon mentioned, it says "connect GND on Tessel to both GND wires from the neopixels" however, I'm working with the individual 'breadboard-friendly' NeoPixels (based on the earlier S model with 6 pins instead of the newer B model with just 4) rather than the strands so I only have one GND pin on the input side. Do I need to wire up the GND from the Tessel GPIO bank or can I just connect the + and - from my power supply directly to the +V and GND of the first pixel? If not, how should I be wiring them up?

Andy

[karl_34]

Your Tessel and the power supply need to share a common ground. You have the extra pins on the breadboard friendly modules so that you can chain the power, ground, and io from module to module.

[andy_mcdonald]

Cheers @karl_34

So if I understand correctly, it doesn't matter if I connect the GND on the Tessel to either the GND pin on the first pixel OR the negative terminal of the power supply so long as it is connected to one of them right?

[karl_34]

@andy_mcdonald -

The GND pin on the Tessel, GND pin on the first pixel, and negative terminal of your power supply will all be connected together. See the first image at https://learn.adafruit.com/adafruit-neopixel-uberguide/arduino-library. Although that's for a strip, it's relevant to your setup.

The signal pin from your Tessel will be connected to the 'In' on the breadboard NeoPixel.

The positive terminal of your power supply will be connected to '+' on the breadboard NeoPixel.

Karl

[andy_mcdonald]

Perfect! I'm with you now @karl_34 - my university electronics classes are coming back to me now.

Thanks for all the help!

[andy_mcdonald]

Number Jonny 5 is alive! We have lights!

[jon]

Fantastic! Nice job, @andy_mcdonald!

[andy_mcdonald]

Hi @jon,

Just wondering if the neopixels firmware is compatible with the other Tessel modules. Specifically, I'm trying to connect the ambient module to allow the neopixels to respond to sound however, when I try the simple examples, the 'ready' event is not firing. My ambient module is on firmware 0.1.8 if that helps.

Cheers... Andy

[jon]

Hey @andy_mcdonald,

Last weekend I put a rebased version of the noepixel library on the build server. If you haven't already try downloading it (same url) and flashing the Tessel again. Let me know if the issue persists!

-Jon

[andy_mcdonald]

Hi @jon,

I did as you said and updated the neopixels firmware but now I get the following error:

Error: Error retrieving Ambient firmware version
stack traceback:
	/app/node_modules/ambient-attx4/index.js:244: in function 'callback'
	builtin/tessel.js:1038: in function 'f'
	[T]: src/colony/lua/colony-node.lua:54: in function <[T]: src/colony/lua/colony-node.lua:53>

This seems to be similar to this issue. @evan suggests downgrading to firmware build 0.1.7 but that would obviously override the custom neopixels build. Is there a way to update the ambient module's firmware independently of the main Tessel firmware? I've tried adding the following line of code:

ambientLib.updateFirmware( tessel.port['A'], '../node_modules/ambient-attx4/firmware/src/ambient-attx4.hex');

...but then I just get the following readout before the app exits.

New Ambient module firmware available - updating...

Any ideas?

Andy

[jon]

Hey Andy,

I see the issue. Tomorrow morning, I can generate a new build which would basically take this Neopixel branch commit and uncomment this line which is critical to SPI comms (which modules like Ambient need). If you've got some free time and build tools installed you can take a stab at compiling your own firmware with that one line change.

-Jon

[andy_mcdonald]

Thanks @jon,

I'll leave this one for you. Please let me know when I can update.

Cheers... Andy

[andy_mcdonald]

Hi @jon,

Did you get a chance to update the neopixel firmware build? I'm attempting to compile my own firmware as you suggested but when I run 'make arm' I get the following error:

make: *** No rule to make target `arm'.  Stop.

I've not touched the Makefile which looks OK to me:

ENABLE_TLS ?= 1
COLONY_STATE_CACHE ?= 0
COLONY_PRELOAD_ON_INIT ?= 0

CONFIG ?= Release

compile = \
	AR=arm-none-eabi-ar AR_host=arm-none-eabi-ar AR_target=arm-none-eabi-ar CC=arm-none-eabi-gcc gyp $(1) --depth=. -f ninja-arm -D builtin_section=.text -D COLONY_STATE_CACHE=$(COLONY_STATE_CACHE) -D COLONY_PRELOAD_ON_INIT=$(COLONY_PRELOAD_ON_INIT) -D enable_ssl=$(ENABLE_TLS) &&\
	ninja -C out/$(CONFIG)

.PHONY: all

all:

clean:
	ninja -v -C out/Debug -t clean
	ninja -v -C out/Release -t clean

nuke: 
	rm -rf out build

update:
	git submodule update --init --recursive
	npm install
	(cd deps/runtime; npm install)
	(cd test; npm install)


# Targets

firmware:
	$(call compile, firmware.gyp)

arm: firmware
	arm-none-eabi-size out/$(CONFIG)/tessel-firmware.elf out/$(CONFIG)/tessel-boot.elf out/$(CONFIG)/tessel-otp.elf

arm-deploy: arm deploy

deploy:
	tessel dfu-restore ./out/$(CONFIG)/tessel-firmware.bin

Not sure where to go from here. Any help would be greatly appreciated.

Cheers... Andy

[jon]

Hey Andy,

I wanted to wait until we solved the root cause of the ambient firmware issue before updating the neopixel lib. The fixes were merged into firmware and ambient code bases yesterday so I rebased neopixels on top of master this morning.

Go ahead and redownload and flash the Neopixel build then npm update your ambient Node module. I haven't had a chance to break out my neopixels and test it so let me know if it doesn't work.

[andy_mcdonald]

Hi @jon,

I've got a spare couple hours so I flashed the new firmware and did an npm update ambient-attx4 however, when I run my code I'm still getting the same error about the ambient firmware:

Error: Error retrieving Ambient firmware version
stack traceback:
	/app/node_modules/ambient-attx4/index.js:245: in function 'callback'
	builtin/tessel.js:1031: in function 'f'
	[T]: src/colony/lua/colony-node.lua:54: in function <[T]: src/colony/lua/colony-node.lua:53>

The ambient firmware is version 0.1.9 so it seems to have updated successfully.

-Andy

[jon]

Hey @andy_mcdonald,

Does Ambient work without the Neopixels plugged in?

I recommend trying this Ambient update procedure.

-Jon