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lamatrix/README.md
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Table of Contents generated with DocToc

Animated LED matrix display

This is a project to drive a 8x32 (or 8x8) LED matrix based on the popular WS2812 RGB LEDs using a microcontroller and optionally control them both using a more powerful host computer, such as a Raspberry Pi Zero W.

The microcontroller is used to provide the accurate timing signals needed to control the WS2812 LEDs. The microcontroller exposes a custom API over its USB serial interface to allow a more powerful computer to treat the display as a framebuffer connected over a serial link.

Currently this microcontroller can be either a Teensy 3.1/3.2 or one of Pycom's development boards running MicroPython (e.g. WiPy 3.0). For the Teensy, an Arduino sketch is provided which controls the WS2812 LEDs using the FastLED library and implements the serial protocol expected by the host software. For boards running MicroPython a corresponding Python implementation is provided.

The host software is written in Python to allow for rapid development.

Features:

  • button input(s)
  • clock (short-press button to toggle between time and date)
  • weather
  • random animations

Static picture with clock scene. For some reason the colors aren't captured as vidvid as they are in real life.

LED matrix with clock scene

Running the Python scripts

For Debian/Ubuntu derived Linux systems, try:

sudo apt install -y python-requests python-serial

On macOS, install pyserial (macOS already ships the requests module):

sudo -H easy_install serial

NOTE: There are known issues with hardware flow control and the driver/chip used in the Pycom modules (e.g. WiPy, LoPy). This causes the host side scripts to overwhelm the microcontroller with data. There do not appear to be any such issues with the Teensy on macOS. There are no known issues with either module with recent Linux distributions, including Raspbian.

Connect the LED matrix to the microcontroller and then connect the microcontroller to your computer (via USB). You should now be able to command the microcontroller to drive the display with:

python main.py

NOTES:

  • The animation scene expects animated icons from a third-party source. See the animations/README.md for details on how to download them.
  • The weather scene expects animated icons from a third-party source. See the weather/README.md for details on how to download them.

Building and deploying the MCU

The host-side Python code expects to be able to talk to the microcontroller over a serial protocol (running on top of USB serial). Software that speaks this special protocol and can talk to the LED matrix needs to be loaded onto the microcontroller.

Arduino

Assuming you have an MCU which is supported by Arduino, try:

  1. Download the latest version of Arduino
  2. In the Library manager, found via the menu entry Tools > Manage Libraries..., search for fastled and install the package
  3. If you have a Teensy 3.x MCU, install the Arduino software add-on Teensyduino from https://www.pjrc.com/teensy/td_download.html
  4. Connect the MCU to your computer using an USB cable
  5. Open the Arduino sketch (project)
  6. Setup the board under the Tools menu, e.g. for a Teensy board:
  • Board: Teensy 3.2 / 3.1
  • Port: /dev/tty.usbmodem575711 (exact path might depend on the specific board and OS)
  1. Build (compile) the sketch via the menu entry Sketch > Verify/Compile
  2. Upload the newly built sketch to the MCU via the menu entry Sketch > Upload

MicroPython

Connect your Pycom module to your computer via USB (or 3.3v serial). Open a serial connection to the module and configure WiFi in the REPL like this:

from network import WLAN
wlan = WLAN(mode=WLAN.STA)
wlan.connect('yourSSID', auth=(WLAN.WPA2, 'yourPassword'))

Connect to the Pycom module's native FTP server and login with micro / python.

Upload the following files to /flash:

Upload the following files to /flash/lib:

Create a new directory under /flash/animations and upload any animation icons referenced in config.json (see animations/README.md for details).

Create a new directory under /flash/weather and upload animated weather icons (see weather/README.md for details).

If you haven't already, you probably want to read Wiring things up.

Configuring the Raspberry Pi

If you want to run the Python scripts, install the necessary Python packages:

sudo apt install -y python-requests python-serial
# On Raspberry Pi Zero importing the Python `requests` package takes 20+ seconds
# if the python-openssl package is installed (default on Raspbian).
# https://github.com/requests/requests/issues/4278
#
# Uninstall it to speed up loading of `weatherscene.py`
sudo apt purge -y python-openssl

Install the support files:

Assuming you've cloned this repo at /home/pi/lamatrix, proceed as follows:

sudo apt install -y python-requests python-serial
cd ~/lamatrix

# Download animated weather icons (refer to weather/README.md)
curl -o weather/weather-cloud-partly.json https://developer.lametric.com/api/v1/dev/preloadicons?icon_id=2286
curl -o weather/weather-cloudy.json https://developer.lametric.com/api/v1/dev/preloadicons?icon_id=12019
curl -o weather/weather-moon-stars.json https://developer.lametric.com/api/v1/dev/preloadicons?icon_id=16310
curl -o weather/weather-rain-snow.json https://developer.lametric.com/api/v1/dev/preloadicons?icon_id=160
curl -o weather/weather-rain.json https://developer.lametric.com/api/v1/dev/preloadicons?icon_id=72
curl -o weather/weather-snow-house.json https://developer.lametric.com/api/v1/dev/preloadicons?icon_id=7075
curl -o weather/weather-snowy.json https://developer.lametric.com/api/v1/dev/preloadicons?icon_id=2289
curl -o weather/weather-thunderstorm.json https://developer.lametric.com/api/v1/dev/preloadicons?icon_id=11428

# Install and start services
chmod +x main.py raspberry-pi/gpio-shutdown.py
sudo cp raspberry-pi/gpio-shutdown.service /etc/systemd/system
sudo cp raspberry-pi/lamatrix.service /etc/systemd/system
sudo systemctl daemon-reload
sudo systemctl enable gpio-shutdown.service lamatrix.service
sudo systemctl start gpio-shutdown.service lamatrix.service

NOTE: If you're not running under the pi user or have placed the files somewhere else than /home/pi/lamatrix you will have to update the ExecPath=, User= and Group= attributes in the .service files accordingly.

Your Raspberry Pi will now poweroff when board pin number 5 (a.k.a BCM 3 a.k.a SCL) goes LOW (e.g. is temporarily tied to ground). The shutdown process takes 10-15 seconds. The Pi can be powered up by again temporarily tying the pin to ground again.

To actually make use of the remote shutdown and reboot feature you need to physically wire the microcontroller to the Raspberry Pi. Connect the microcontroller's GND (ground) to one of the GND pins on the Raspberry Pi. Connect pin 14 (see HOST_SHUTDOWN_PIN in ArduinoSer2FastLED.ino) on the microcontroller to the Raspberry Pi's BCM 3 a.k.a SCL.

Optional steps

If you're running a headless Raspberry Pi you can reduce the boot time by a few seconds with:

sudo apt-get purge -y nfs-common libnfsidmap2 libtirpc1 rpcbind python-openssl
grep -q boot_delay /boot/config.txt || echo boot_delay=0 |sudo tee -a /boot/config.txt
sudo systemctl disable dphys-swapfile exim4 keyboard-setup raspi-config rsyslog

(the python-openssl package slows down the import of the python-requests package: https://github.com/requests/requests/issues/4278)

Hardware

LED matrix display

On popular auction sites there are 8x8, 8x32 and 16x16 flexible LED matrix displays with WS2812 LEDs if you search for e.g. LED Matrix WS2812 5050 flexible:

chinese-8x32-ledmatrix.jpg.

Price: €35-45

For the 8x32 variant, you can 3D print a frame from these objects:

For diffusing the light emitted by the LEDS a paper works suprisingly well if it's tightly held to the grid.

MCUs

Both alternatives support both Arduino and MicroPython.

NOTE: it seems that hardware flow control between pyserial and the Pycom modules (e.g. WiPy, LoPy) doesn't work properly for some reason. This results in the host overwhelming the microcontroller with data, leading to data loss in the serial protocol which in turn messes up what is displayed on the LED matrix. The Teensy 3.x boards work without problems however.

Teensy 3.1/3.2 pinout

Teensy 3.1/3.2 pinout

Source: https://www.pjrc.com/teensy/teensyLC.html

WiPy 3.0 pinout

WiPy 3.0 pinout

Source: https://docs.pycom.io/datasheets/development/wipy3.html

Raspberry Pi

Newer Raspberry Pi computers have a non-populated RUN pin (marked with a square) that, if tied to ground, will reset the Pi's CPU. See this answer on What are the RUN pin holes on Raspberry Pi 2?.

Since there is a 10k pull-up resistor connected to this pin, the Pi will turn on again when this pin is no longer tied to ground. The drawback is of course that resetting the CPU leads to an unclean shutdown of the Pi, which in turn might lead to SD card corruption.

A Raspberry Pi which has previously been shutdown using e.g. sudo poweroff can be brought back to life by temporarily grounding GPIO 5 (a.k.a BCM 3 a.k.a SCL). With the help of a small Python script running in the background we can make GPIO 5 an input pin and watch for level changes. If this pin becomes LOW (i.e. tied to ground) we can initiate a clean shutdown with sudo systemctl poweroff --force.

Example from raspberry-pi/gpio-shutdown.py:

#!/usr/bin/python
#
# Watch the board pin number 5 for level changes and initiate a power-off
# when this pin goes low.
#
from RPi import GPIO
from subprocess import call

# https://pinout.xyz/pinout/i2c
pin = 5  # a.k.a BCM 3 a.k.a SCL

GPIO.setmode(GPIO.BOARD)
GPIO.setup(pin, GPIO.IN)
GPIO.wait_for_edge(pin, GPIO.FALLING)
print('GPIO 5 dropped to low, initiating poweroff')
call(["/bin/systemctl","poweroff","--force"])

On the serial protocol

Because of the limited amount of memory available on MCU it was decided to use a more powerful computer to render things on the LED matrix display. The most natural way of connecting a MCU and a host computer is to use the serial interface available on many popular MCUs, and thus a serial protocol was born.

To add new functionality to the serial protocol, ensure that you make the necessary updates in:

  • the MCU implementation on the Arduino side, in and around loop()
  • the MCU implementation on the MicroPython side, in pycomhal.py
  • the host computer implementation, in arduinoserialhal.py

Hacking

In short:

  • on the host-side, everything starts in main.py
    • somewhat confusingly this file is also the entrypoint for microcontrollers running MicroPython
  • main.py has a RenderLoop which consumes scenes (e.g. a clock scene, a weather scene, ..)
  • a framebuffer wrapper around the LED matrix display is in ledmatrix.py
    • this is used primarily for the host-side but is also used on microcontrollers running MicroPython
  • the framebuffer wrapper does low-level display operations via a HAL (hardware abstraction layer)
    • on the host-side this is implemented in arduinoserialhal.py
    • on the host-side this file pretty much opens a serial port and speaks a custom protocol to command the microcontroller to do things
  • on the microcontroller-side the custom protocol is implemented in:

To add a new scene, create a Python module (e.g. demoscene.py) like this:

#!/usr/bin/env python
class DemoScene:
    """This module implements an example scene with a traveling pixel"""

    def __init__(self, display, config):
        """
        Initialize the module.
        `display` is saved as an instance variable because it is needed to
        update the display via self.display.put_pixel() and .render()
        """
        self.display = display
        self.x_pos = 0  # ..just an example
        print('DemoScene: yay, initialized')

    def reset(self):
        """
        This method is called before transitioning to this scene.
        Use it to (re-)initialize any state necessary for your scene.
        """
        self.x_pos = 0
        print('DemoScene: here we go')

    def input(self, button_id, button_state):
        """
        Handle button input
        """
        print('DemoScene: button {} pressed: {}'.format(button_id, button_state))
        return False  # signal that we did not handle the input

    def render(self, frame, dropped_frames, fps):
        """
        Render the scene.
        This method is called by the render loop with the current frame number,
        the number of dropped frames since the previous invocation and the
        requested frames per second (FPS).
        """

        time_in_seconds = frame * fps
        if not time_in_seconds.is_integer():
            # Only update pixel once every second
            return True

        y = 3
        color = 64
        self.display.clear()
        self.display.put_pixel(self.x_pos, y, color, color, color >> 1)
        self.display.render()
        print('DemoScene: rendered a pixel at ({},{})'.format(self.x_pos, y))

        self.x_pos += 1
        if self.x_pos == self.display.columns:
            return False   # our work is done!

        return True   # we want to be called again

if __name__ == '__main__':
    display = None
    config = None
    scene = DemoScene(display, config)
    scene.reset()

Then open main.py and locate the following line:

r = RenderLoop(display, fps=10)

Below it, create an instance of your module and call RenderLoop.add_scene() to add it to the list of scenes. If your module is named demoscene.py and implements the DemoScene class it should look something like this:

from demoscene import DemoScene
scene = DemoScene(display, config['DemoScene'])
r.add_scene(scene)

You should also add a "DemoScene": {}, block to the config file config.json. Store any settings your scene needs here.

With these steps completed, the scene's render() method should now eventually be called when you run the host-side software (e.g. python main.py). The method should return True until you're ready to hand over control to the next scene, in which case you signal this by returning False.

Wiring things up

To the extent possible I've attempted to choose the same set of board pins on both MCUs (microcontrollers).

A short note on pin mappings:

  • physical pin numbering refer to the chip's physical pins
  • GPIO pin number refer to the chip's internal GPIO pin numbering (e.g. GPIO22 as shown in pinout mappings)
  • board pin numbering refer to the pins as made available on the PCB, with pin 0 or 1 often being in the top left corner after excluding any power/ground/reset pins
  • pin ID as mapped in firmware, e.g. digital pin number 10 or P10 (as shown in pinout mappings)

LED matrix

Connect the display like this:

LED matrix:  5V --> MCU: Vin pin (voltage in)
LED matrix: GND --> MCU: GND pin
LED matrix: DIN --> MCU: digital pin 6 on Teensy; P11 (a.k.a GPIO22) on Pycom module

Button

Connect the button like this:

Button pin 1 --> MCU: digital pin 12 on Teensy; P12 (a.k.a. GPIO21) pin on Pycom module
Button pin 2 --> MCU: GND pin

Connecting second UART on Pycom module to Raspberry Pi

To connect the Pycom module's (e.g. WiPy) second UART (3.3V serial port) to the Raspberry Pi's UART, connect:

Raspberry Pi: board pin  8 (TXD) --> MCU: P4 (a.k.a RX1 a.k.a GPIO15) on Pycom module
Raspberry Pi: board pin 10 (RXD) --> MCU: P3 (a.k.a TX1 a.k.a GPIO4) on Pycom module
Raspberry Pi: board pin  6 (GND) --> MCU: GND pin

NOTE: Raspberry Pi modules with built-in WiFi/Bluetooth needs the following line in /boot/config.txt to free up the TXD/RXD pins:

dtoverlay=pi3-disable-bt

Running screen /dev/serial0 115200 on the Raspberry Pi should now allow you to see data sent from the MCU's second UART.

Remote power management for Raspberry Pi

To let the MCU manage the Raspberry Pi's power, connect:

Raspberry Pi: board pin 5 (a.k.a SCL) --> MCU: digital pin 8 on Teensy; P8 (a.k.a GPIO2) on Pycom module
Raspberry Pi: board pin 6 (a.k.a GND) --> MCU: GND pin

Credits

Several animations in the form of .json files were backed up from LaMetric's developer API. Credit goes to the original authors of these animations.

The urequests.py file is a slightly modified copy from micropython/micropython-lib.

The ws2812.py file, a MicroPython implementation for controlling WS2812 LEDs, is based on work published on JanBednarik/micropython-ws2812.

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