Arduino code 2020-21

Overview

Low-level software for the Newcastle University ROV 2021. Takes key:value pairs from Raspberry Pi in MsgPack format and acts on them accordingly.

Designed for Arduino Nano 33 BLE but should also be fully functional for Arduino Mega 2560 or similar.

Installation

Software Dependencies

You need to install the following libraries in your IDE:

• ArduinoJson
• Servo

Identification

Arduino A and Arduino B have different pin assignments as shown below. By default, the code assumes it is running on Arduino A. To switch it to Arduino B, connect pin 17 to GND.

Device keys and pin allocation

Thrusters are given an ID which describes their position on the ROV. Motors are named in a similar fashion.

Device Name	Key	Attached to	Pin	Location
Top Forward Port Thruster (front left)	T_VFP	Arduino A	2	Enclosure 1
Top Forward Starboard Thruster (front right)	T_VFS	Arduino A	3	Enclosure 1
Top Aft Port Thruster (back left)	T_VAP	Arduino A	4	Enclosure 1
Top Aft Starboard Thruster (back right)	T_VAS	Arduino A	5	Enclosure 1
Forward Port Thruster (front left)	T_HFP	Arduino B	2	Enclosure 2
Forward Starboard Thruster (front right)	T_HFS	Arduino B	3	Enclosure 2
Aft Port Thruster (back left)	T_HAP	Arduino B	4	Enclosure 2
Aft Starboard Thruster (back right)	T_HAS	Arduino B	5	Enclosure 2
Arm Gripper Motor	M_G	Arduino B	6	Enclosure 2
Micro ROV return cord	M_C	Arduino B	7	Enclosure 2
Micro ROV Thruster	T_M	Arduino B	8	Enclosure 2
Arduino A	A_A	Raspberry Pi		Enclosure 1
Arduino B	A_B	Raspberry Pi		Enclosure 2

Arduino A Behaviour

Incoming data from Pi

Key	Min	Max
T_VFP	1100	1900
T_VFS	1100	1900
T_VAP	1100	1900
T_VAS	1100	1900

Outgoing data to Pi

Key	Min	Max
ID	A_A	A_A
S_A	-	-

Arduino B Behaviour

Incoming data from Pi

Key	Min	Max
T_HFP	1100	1900
T_HFS	1100	1900
T_HAP	1100	1900
T_HAS	1100	1900
M_G	1200	1800
M_C	1350	1650
T_M	1100	1900

Outgoing data to Pi

Key	Min	Max
ID	A_B	A_B
S_B	-	-

Status Codes

These will be returned with the S_A or S_B keys.

Status Code	Description
0	No error
1	Outputs halted
2	Left limit hit. Motor stopped
3	Right limit hit. Motor stopped
4	Arduino booting
5	Heartbeat
-1	Received value out of range
-6	This is not an Output Arduino
-7	This is not an Input Arduino
-8	Invalid Output device key
-9	Invalid Input device key
-10	Can't stop outputs on an Input Arduino
-11	Incoming data parsing failed
-12	Arduino ID is not set up
-13	No messages received, outputs halted
-23	Index not valid for setting a sensor parameter

Status LED

The Arduino Nano has an RGB LED which is used for debugging.

Colour	Meaning
🔴Red	Waiting for data from Pi. Outputs disabled for safety.
🟢Green	Everything working as expected
🔵Blue	Unused
🟡Yellow	Waiting for data from Pi
🟣Purple	Loading/processing data
Cyan	Data parsing successful

Development

Overview

The arduino runs arduino-main.ino which imports from the src directory. In terms of structure, the most interesting parts are in the equipment directory. Each device which could be connected has its own class.

• Input devices (i.e. sensors) inherit functionality from the Input class.
• Output devices (i.e. thrusters, motors) inherit functionality from the Output class.
  • Anything which was using the BlueRobotics PWM controlled motors, including all thrusters and arm motors, has been derived from the EscMotor class.

This code is ultimately the third iteration of the 2018-19 Arduino code.

Mapper

A lot of the code is structured around the Mapper class. This class acts in a broadly similar way to a Java Hashmap. It has key:value pairs where the key is a string (the JSON ID of that device) and the value is an object which inherits from either Input or Output.

Project structure

• arduino-main.ino
• src
  • communication
    • communication.h
    • communication.cpp
  • equipment
    • input
      • input.h
      • input.cpp
      • None this year but past sensors can be found in the 2019-20 codebase.
    • output
      • armgripper.h
      • armgripper.cpp
      • armrotation.h
      • armrotation.cpp
      • cord.h
      • cord.cpp
      • genericEscMotor.h
      • genericEscMotor.cpp
      • output.h
      • output.cpp
      • thruster.h
      • thruster.cpp
  • util
    • constants.h
    • constants.cpp
    • id.h
    • id.cpp
    • led.h
    • led.cpp
    • mapper.h
    • mapper.cpp
    • status.h
    • status.cpp

Control of motors

All motors in this implementation are the Blue Robotics T100/T200/M100 which are controlled via PWM. Each of these classes inherits from the EscMotor class, which in turn inherits from Output. You set the speed of the motor using the setValue() method. For these motors it will take values in the range 1100-1900, where 1500 is stopped. Devices are controlled when an associated key:value pair is received from the Pi.

Reading of sensors

Sensors all inherit from the Input base class. You can read the sensor value from the getValue() method, and set any attributes of that sensor with setParam(). Sensors are polled once per loop.