arduino_daq

This package contains an AVR8 firmware, a host standalone C++ library, and a ROS node for UAL eCAR’s Arduino-based DAQ system, but it is generic enough for use in many other applications.

The DAQ features: 4 analog outputs (via an optional MAX5500 chip), ADC inputs, GPIO and PWM outputs, 2 channels quadrature encoder decoding support, and one absolute encoder (EMS22A) input. Outputs feature an optional watchdog timer that resets the output if not updated periodically (default period is 1 second).

The precompiled firmware is for atmega328P, but it could be recompiled for other larger versions with more I/O pins.

Valid pin numbers

The function of each pin can be configured on the fly from the host (PC) software. Naturally, each microcontroller hardware limits some special functions:

• atmega328P
  • GPIO inputs/outputs: 2-13
  • ADC inputs: 0-8
  • PWM outputs: pins 3, 5, 6, 9, 10, and 11.
  • Quadrature encoders:
    • Encoder #0:
      • Channel A must be pin 2.
      • Channels B & Z can be any free GPIO pin.
    • Encoder #1:
      • Channel A must be pin 3.
      • Channels B & Z can be any free GPIO pin.

Compiling

In GNU/Linux or Windows, use CMake to generate the Makefiles or project files as usual. Set CMake variables BUILD_ROS and BUILD_STANDALONE_LIB to ON/OFF depending on whether you want to compile a ROS node or a standalone C++ library.

For compilation within a ROS catkin environment, simple clone this repository inside your ~/catkin_ws/src/ and run catkin_make.

Prerequisites:

    sudo apt install libmrpt-dev

ROS examples of use

Note: Numering of pins follows the Arduino pin number convention (for example: Arduino ProMini,ATmega328, pin: PB1 <=> chip pin number: 13 <=> Arduino pin number: 9 ).

• First: Launch the node with

   roscore     # In one terminal
   rosrun arduino_daq arduino_daq_node _SERIAL_PORT:=/dev/ttyUSB0    # In another terminal
  

Next, in another terminal try any of the following:

• Setting a DAC analog value (volts):

    rostopic pub /arduino_daq_dac0 std_msgs/Float64 1.5
  

• Setting a GPIO digital output pin:

    rostopic pub /arduino_daq_GPIO_output7 std_msgs/Bool 1
  

• Setting a PWM output (0…255 maps to 0%…100% duty cycle):

    rostopic pub /arduino_daq_pwm3 std_msgs/UInt8 220
  

• Automatically starting ADC sampling at 10 Hz, with 5V reference voltage, on two channels in pins ADC0 and ADC1 (Requires killing arduino_daq to launch it again with these parameters).

    rosrun arduino_daq arduino_daq_node _SERIAL_PORT:=/dev/ttyUSB0 _ADC_INTERNAL_REFVOLT:=0 _ADC_MEASURE_PERIOD_MS:=100 _ADC_CHANNEL0:=0 _ADC_CHANNEL1:=1
  

• Automatically starting reading an ENCODER sampling at 10 Hz, on one channel with Channel A=pin 2, Channel B=pin 8, and Channel Z=pin 9 (set channel Z to “0” if not wired). (Requires killing arduino_daq to launch it again with these parameters).

    rosrun arduino_daq arduino_daq_node _SERIAL_PORT:=/dev/ttyUSB0 _ENC0_PIN_A:=2 _ENC0_PIN_B:=8 _ENC0_PIN_Z:=9
  

• Example use of a EMS22A absolute encoder: “, pin_cs);

    rosrun arduino_daq arduino_daq_node _SERIAL_PORT:=/dev/ttyUSB0 _ENCABS0_PIN_CS:=1  _ENCABS0_PIN_CLK:=2  _ENCABS0_PIN_DO:=2 _ENCABS_MEASURE_PERIOD_MS:=100
  

ROS graph

Source code directories

• arduino_firmware: Contains an AtmelStudio project for the firmware. Written in C++ using the Arduino library.
• include and libarduinodaq: Standalone C++ library.
• src: ROS node

Frame format

Communication PC <-> arduino happens based on data frames as follow:

     START_FLAG   |  OPCODE  |  DATA_LEN   |   DATA      |    CHECKSUM    | END_FLAG |
       0x69          1 byte      1 byte       N bytes       =sum(data)       0x96

The complete list of OPCODES and associated payload DATA fields are defined in the C++ header file arduinodaq2pc-structs.h, which is #included in both, host C++ libraries and the embedded firmware.

Programming the microcontroller

For an Atmega328p (“Arduino Mini Pro”), use this command line from the root directory of this repository:

    avrdude -p atmega328p -c arduino -P /dev/ttyUSB0 -b 57600 -U flash:w:"arduino_firmware/arduino_daq/arduino_daq/Release/arduino_daq.hex":i