RGB LED HAT (B)

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RGB LED HAT (B)
True color RGB LED HAT (B) for Raspberry Pi, colorful display, 8 × 8 grid
Rgb-led-hat-b-intro.jpg

True color RGB LED HAT (B) for Raspberry Pi, colorful display, 8 × 8 grid
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Primary Attribute
Category: Expansions, Raspberry Pi
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Brand: Waveshare
Website
English: Website
Chinese: 官网
Onboard Interfaces
RPi
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Introduction

True color RGB LED HAT (B) for Raspberry Pi, colorful display, 8 × 8 grid

More

Interfaces

  1. For Raspberry Pi, you only need to insert the product to the corresponding interface on the Pi;
  2. The PH2.0 3P connector is used for other devices.
Symbols Pin descriptions
5V 5V power supply
GND Ground
DIN Control signal input

Description

WS2812B is an intelligent LED controller of which the control circuit and the RGB chip are integrated in a package of 5050 components. It internally includes an intelligent digital port, a data latch and a signal reshaping amplification drive circuit. To ensure the color brightness consistent of the pixel light, it also contains a precision internal oscillator and a 12V voltage programmable constant current control part.

Its data transfer protocol uses single NZR communication mode. After the pixel is power-on and reset, the DIN port receives the data from the controller. The first 24 bit data is collected by the first pixel, and then sent to the internal data latch. The other data are reshaped by the internal signal reshaping amplification circuit and sent to the next cascade pixel through the DO port. After the transmission for all pixels, the signal may reduce to 24bit. The pixel adopts auto reshaping transmit technology, which allows the pixel cascade number is up to the speed of the signal transmission but not bound by the signal transmission restriction. For more information about auto reshaping transmit technology, please refer to the section data transfer protocol.

Sequence chart

Sequence chart
  • Data transfer time( TH+TL=1.25µs±600ns)
T0H 0 code, high voltage time 0.4µs ±150ns
T1H 1 code, high voltage time 0.8µs ±150ns
T0L 0 code, low voltage time 0.85µs ±150ns
T1L 1 code, low voltage time 0.45 µs ±150ns
RES The unit of frame, low voltage time Above 50µs

Data transmission method

Data transmission method

On the base of the data sequence, we can easily complete data transfer with the communication protocol.

Note: The data of D1 is send by MCU, and D2, D3, D4 are transmitted through pixel internal reshaping amplification.

  • Composition of 24bit data:
G7 G6 G5 G4 G3 G2 G1 G0 R7 R6 R5 R4 R3 R2 R1 R0 B7 B6 B5 B4 B3 B2 B1 B0
Note: The data is sent in the order of GRB and the high bit is sent at first.

How to use

Perhaps the descriptions above is too verbose to understand but you can skip it and just use the corresponding libraries in your Raspberry Pi. In this case, you should copy the example program packages to your Pi and unzip them.

Libraries installation

Copy the file rpi_ws281x-master.zip to your Pi, and run the following line to unzip it.

unzip rpi_ws281x-master.zip

For the latest libraries, you can visit the website: https://github.com/jgarff/rpi_ws281x

Install the depended-upon software

sudo apt-get install build-essential python-dev scons swig

Compile the program

cd rpi_ws281x-master
sudo scons
Rgb-led-hat-user-manual-3.png

Run the line below to perform testing. You can see the RGB LED flickering.

sudo ./test

Run the following line to install the python library.

cd python 
sudo python setup.py install

Run the demo code for testing.

cd examples
sudo python lowlevel.py
  • If the library is installed successfully, you can see the RGB LED flickering.

  • If the LED displays the wrong color, please add the lines below into the file /boot/config.txt, and restart the Pi to take them effect.
  • RGB LED adopts DMA control, which may occupy the video output DMA channel on the Raspberry Pi. Therefore, adding these lines may cause the earphone connector unusable.

hdmi_force_hotplug=1
hdmi_force_edid_audio=1

Demo descriptions

Running the demo ws2812.py, you can see the RGB LED display the gradient color.

cd RGB_LED_HAT
sudo python ws2812.py
Rgb-led-hat-b-user-manual-1.png
  1. from neopixel import * import the library rpi-ws281x
  2. Adafruit_NeoPixel creates an object strip, sets the number of the LEDs to 32, the pin to 18, and the frequency to 800000. The parameter LED_BRIGHTNESS is the brightness of the LED.
  3. begin() RGB LED initialization function.
  4. setPixelColor(pos, color) This sets the pixel, of which pos is the LED position, and color is the RGB color
  5. color(r, g, b) This converts the RGB value to a 24 bit color.
  6. show() This transfers data, showing the set LED color.
  7. For more information about the functions, please see rpi_ws281x-master/python/neopixel.py

Web control with Bottle

controlled by browser

Bottle is a fast, simple and lightweight WSGI micro web-framework for Python. By Bottle, you can fast and easily implement Web control.

Install the library

sudoapt-get install python-bottle

Perform web control RGB LED via Bottle

cd ~/RGB LED HAT/web-RGB
sudo python main

Then, enter the IP address of your Pi and the port number 8000 into the address bar of the browser. Clicking different position of the palette, the LEDs will display different colors. There are 3 display modes selectable, static, breath and flash.

  • Note: This web-RGB program only supports the mobile phone browser. It is unavailable for PC browser.

Resources

Documentation

Software

Others

Support

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