RC Car
This build primarily focuses on multiple software and electrical design skills. Consisting of FreeRTOS, Bluetooth, and Flutter app design, I hope to make an immersive device that is capable of functioning seamlessly
FreeRTOS - Tasks
Motor Control
This task is being developed to perform the following functions:
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Handles movement of the car based on updated values.
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Takes received values from Bluetooth Communications task
Priority: Medium ​
Debugging
This task is being developed to perform the following functions:
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This task will be used for the main priority of updating debug logs and keeping information in case of any issue
Priority: Low​
App Updating
This task is being developed to perform the following functions:
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When free space is available, this task will send updated values to the Bluetooth comm task for the purpose of updating the smartphone app
Priority: Low​
Bluetooth Communication
This Task is being developed to perform the following functions:
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Manages input and output from Bluetooth module.
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It will listen for incoming commands and will update other tasks
Priority: Medium​
Sensor Reading
This Task is being developed to perform the following functions:
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Will read sensors within the car and update global variables
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Will send updates to the motor control, app updating and safety tasks
Priority: Medium - Low​
Safety Task
This Task is being developed to perform the following functions:
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This task will be on standby reading sensor data. In the case of an emergency, the safety task will deal with it accordingly.
Priority: Highest​
Task Management
Semaphores
The Semaphore is a synchronization mechanism built into FreeRTOS that will allow for the management of shared resources between multiple tasks. I plan to use a semaphore between different tasks such as the sensor reading task and the UI updating task so that measured values will be displayed on the app interface.
Queue
The Queue is great for constant inter-task communication. They allow for a safe, synchronized messaging system which would great for tasks on the same priority level. In our case, it would be great for communication between the Bluetooth communications task and the motor control task as this would allow for constant data transfer as seen between the app and the Bluetooth module.
Mutexes
The Mutex in FreeRTOS is great for situations where multiple tasks can access the same global variable. This will protect the variable while one task is accessing it and will schedule others to access it later.
Event Group
The event group is a synchronization mechanism that makes tasks wait for a specific situation or set of events to occur before being set into motion. In our context, this would be useful for the safety task as it will wait for a situation of emergency before setting task into play.
Electrical Components
HC-05 Bluetooth Module
The HC-05 is a 6-pin Master/Slave Classical Bluetooth Module that enables full duplex wireless communication. It follows the Serial UART communication interface which allows it to connect to the TX/RX pins on the Arduino Uno. Its communication range of 10 Meters made it great for my RC car as I did not require extreme range as I expected to be near the car at all times. This module operates on a 3.3V supply voltage, whereas the Arduino operates on a 5V supply. This meant that a voltage conversion circuit was required to step down the TX signals from the Arduino.
L298P Motor Controller
The Keyestudio Motor controller is an Arduino Shield that takes advantage of the L298P H-Bridge IC to provide bi-directional motor control for up to 2 motors. The Shield has 2 Direction pins(12, 13), and 2 PWM pins(3, 11), which are directly interfaced with their corresponding Arduino Pins. The shield has a direct voltage source that can handle up to 46V and 2A per motor channel. In our context, this shield will be used to control the speed and direction of the two rear motors.
Arduino Uno
The Arduino Uno is a development board that employs the ATmega328P Microcontroller. It features, 32KB of flash memory, 2KB of SRAM and 1KB of EEPROM data storage. It has 6 Analog input pins making it capable of handling multiple external sensors and 12 digital input/output pins. with a select few capable of Pulse Width Modulation. The board also has built-in UART communication allowing it to communicate with alternative boards such as the HC-05. The board functions with a 5V supply voltage which allows for the board to directly power many external circuits.
MPU-6050
The MPU-6050 is an IC that combines an Accelerometer and a Gyroscope. The Gyroscope is a 3-axis and it can measure angular velocity on the X, Y and Z axes. The Accelerometer is capable of measuring acceleration on all 3 Axes which allows for measuring changes in linear motion and orientation.
Preliminary Design Decisions
Decision 1
This design is the base design that I developed for the car prior to getting the motor controller shield. I decided to go with the L293D H-Bridge as seen in the second board below. However as it required 4 separate PWM pins to allow for fine motor control, I decided to opt for an alternative.
Decision 2
Prior to the HC-05 Bluetooth Module, I opted for an IR control. However, this option was removed as it did not provide enough range and obstructions would cause signal issues. On the other hand, while Bluetooth doesn't have the greatest range either, it does however work in any direction and does not require unobstructed view of the reciever.