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PWM Port Example

Package 'nsdk_example_spi':

This package contains two executors: spi_control_subscriber and spi_publisher. This example transforms hex code through SPI to control a chip MAX7219, and this chp contorls an 8x8 LED Matrix. You could translate your image to hex code using this tool on this wedsite: DotMatrixTool.

  1. Executor spi_control_subscriber controls the SPI by using mraa library, when spi_control_subscriber get the message from spi_publisher, it will send hex code through SPI to the MAX7219, and controls the LED Matrix.
  • Run the pwm_control_subscriber of this package by using:
 ros2 run nsdk_example_spi spi_control_subscriber
  1. Executor spi_publisher publishes one message to the topic /spi_control_msg every time you execute it , and in the message contains every hex you send to the program. Composition of the hex data: 0xaabb, aa is for the value you want to set to the address, bb is for the address. Pleace refer to register map of MAX7219 for the mapping of the address.
  • Run the pwn_publisher of this package by using.
ros2 run nsdk_example_spi spi_publisher <LED setup message1(hex)> <LED setup message2(hex)>...
#*Remarks:you should initialize the LED matrix by setting up addresses 0x09, 0x0a, 0x0b, 0x0c, 0x0F before sending data of you image.
ros2 run nsdk_example_spi spi_publisher 0x0009 0x070a 0x070b 0x010c 0x000f  #Example of publishing initial message.
#For example, we could display an arrow by using:
ros2 run nsdk_example_spi spi_publisher 0x1801 0x3c02 0x7e03 0xff04 0x3c05 0x3c06 0x3c07 0x3c08

Register Map Of MAX7219

  • For controlling the display, several registers of MAX7219 need to be set correctly. In the example of this tutorial, six types of registers will baccessed:

    Name / Functionality Address Description
    Decode Mode 0x09 Turn on / off the decode mode
    Intensity 0x0A Adjust the brightness of the display
    Scan Limit 0x0B Determine how many digits are enabled
    Shutdown 0x0C Turn on / off the display module
    Display Test 0x0F Enter the test mode (all LED segments light on) or not
    Digit 0~ Digit 7 data 0x01~0x08 The address to control digit 0 ~ digit 7