Formula Embedded Wiki

Here: Github Repo

Our objective was to build a Data Acquisition System (DAQ) capable of collecting, storing, and transmitting validated data from all on-board equipment to the cloud in real time utilizing a 4G/LTE network. In doing so, current and future CSUN FSAE teams will hold the capability to monitor and benchmark the performance of their vehicle design iterations.

This software is based around ROS and, is meant to run on an Nvidia Jetson Tx2. In addition to this SOC there are other sensors and boards necessary to communicate with other parts of the system. For a full parts list refer to the internal documention found on the Google Drive. If you happen to be visiting take a look below to get an idea of what hardware was used to create this project.

We keep a few things in mind when designing and implementing new features.

1. How maintainable each node will be in the future.
2. How reusable each node will be in the future.

Understanding how ROS messages and processes function is essential in making wise design decisions. Most people are quick to think that by eliminating ROS Nodes the system will become more efficent however this isn't always the case. Additionally it's important to keep in mind that a monolithic system makes each node more difficult to maintain and reduces the reusebility of the software. Therefore when looking to improve the system by either adding additional functionality or making improvements to performance it's important to make sure that each node performs only a single function (e.g. getting data from a single device and publishing its data).

The rest of the sections of the wiki will not necessarily describe individual ROS nodes but instead describe parts of the system refrencing ROS nodes along the way that handle that part of the system. NOTE to maintainers: Update the ROS diagram you wont be the only person developing this so keep the next person informed.

This part of the wiki will assume you have a working OS running with all of the necessary kernel modules enabled in order to interface with the appropriate hardware. For a guide on this sort of stuff look at the "Helpful Links" part of the wiki. Additionally at the time of writing editing this wiki 26 January 2019 21 April 2019 all of our nodes, services, etc. are based off of the ROS Kinetic release.

This is our embedded linux platform where all of our embedded code lives and is responsible for two way telemetery and real time data acquisition. Additional Kernel modules have been compiled in order to support devices such as CAN transcievers. In addition several other dependencies have been installed (if you're new to the project refer to the google drive)

• These transceivers are connected to the Jetson Tx2 using the J26 header.
• See J21/J26 Pinout section for pinout images

The software used to interact with the MCU is held in the ROS node titled CAN_BUS. This node is responsible from sending and receiving messages from the MCU (Motor Control Unit) as well as the BMS (Battery Management System) via the 5 pin Can Bus port on the Unitek motor controller. This Node receives messages from the web based node and publishes data to the web node responsible from telemetry and sends messages out to the rest of the ECU's mentioned above.

• See J21/J26 Pinout section for pinout images

The software to support this device is actually split up into two ROS nodes. The first is located in INERTIAL_MEASUREMENT_UNIT and the other is in BAROMETRIC_PRESSURE_SENSOR. This Waveshare device is actually composed to two separate devices the MPU-9255 and the BMP280 which have two separate addresses on the I2C bus. The MPU-9255 is composed of a gyroscope, accelerometer, and compass. The BMP280 is a pressure/temperature sensor.

• See J21/J26 Pinout section for pinout images

The ROS node for the analog to digital converter is named ANALOG_TO_DIGITAL_CONVERTER its main responsiblity is to make requests to each of the ADS7828 Texas Instrument chips on the ADC board shown above. These requests are sent through write commands and consist of a stream of bits outlined in the data sheet. Becuase each of these ADCs multiplixes between each of the eight channels it has it must be sent a command to read off the right channel.

An arduino uno with an I2C shield was used to interface with the digital sensors. As of the time of writing this its performance is lack luster when calcualting speed. This may be due to its ability to handle the amount of interrupts it's sent while the vehicle is running and may be switched out if it's a hardware limitation.

The software for this part of the system is located in the ROS node titled SPEEDOMOTER. It was decided that the only digital sensors on the car would be for calcualting the speed at which the car was moving therefore a microcontroller was chosen to calculate that for us and then setup the I2C line. Similar to how the Analog to Digital converter works requests for data are made to this device over the bus and the speed in MPH is returned to the Jetson Tx2.

Although this piece of data functions as our method of communication to the outside world (Our Web Server) it also give us a few data points such as Altitude, GPS, and Satalite Data. The communication protocol used for interfacing with this is Serial off of character driver. In order to setup what data is being sent the minicom utility must be used ahead of time before simply reading data off of /dev/tty*USB*. The code can be found in the ROS node labled GPS.