Autonomous Mini Robot Car Explorer Project

Project Description

In this project, you will build an autonomous Robot Car that can autonomously explore a track. Our goals in this project are to understand basic microcontroller hardware components, including GPIO, interrupt, analog to digital conversion (ADC), and hardware PWM, and to build an embedded control system that makes use of those components to interface with switches, LEDs, DC motors, and sensors.

The robot car will autonomously explore a track with two walls, starting at the open end, exploring the whole track, and then returning to the open end where it starts. The shape of the track is unknown, but there will be both left turns and right turns, and the track has no branches. In other words, there is only one way to the closed end and one way back to the open end.

Hardware Requirements

1. PLL is required to set the system clock to be 50MHz using an external clock source.
2. Hardware PWM is required to drive the DC motors.
3. Three IR sensors are required for the robot to detect obstacles around it.
4. GPIO assignments:

GPIO Pins	Devices
PE1	Left IR sensor output
PE4	Front sensor output
PE5	Right IR sensor output
PB6	Hardware PWM output for left motor
PA7	Hardware PWM output for right motor
PB45	Direction pins for left motor
PB23	Direction pins for right motor
PF123	Onboard color LEDs
PF0	Onboard switch 2
PF4	Onboard switch 1

5. Onboard LEDs are used to indicate the status of the robot:

Color	Indication
RED	Robot Car is too close to an obstacle: less than 15cm away.
BLUE	Mission accomplished: the car finished exploring the whole track and back to the open end.
GREEN	Robot Car is traveling in a safe area: at least 10cm away from any obstacles.

Project Highlights

• Embedded Systems project
• Developed an autonomous mini car to complete a lap on a track by programming an ARM-based MCU in C, using 3 IR sensors, 2 DC motors, and assembling a power distribution board.
• Formulated an optimal time complexity distance algorithm based on analog IR sensor signals, increasing distance calculation throughput by 50%.
• Configured a hardware-based Pulse Width Modulation (PWM) to evenly distribute power across 2 stepper motors, allowing fine-tuning of the car’s velocity and alignment.
• Soldered, assembled, and designed schematic.

PLL Configuration

Phase Locked Loop (PLL) is utilized to generate a stable output high frequency from a low frequency signal. The PLL allows us to modify the execution speed of the TM4C microcontroller. Initially, we set the clock frequency to 16MHz to fulfill the project. For the chassis extra credit, we set the frequency to 50 MHz. In order to achieve this frequency, the 400 MHz bus frequency was required to be divided by SYSDIV2+1. The value of 7 in the SYSDIV2 outputs the frequency of 50Mhz since 400Mhz/(7+1) = 50Mhz.

Hardware PWM and DC Motors

Hardware PWM was utilized to control the DC Motors of the robot. Hardware PWM is used to control the power delivered to the DC motors, providing an efficient and accurate way to control current delivered to the motors. The Pololu Motor Driver and Power Distribution Board features two DRV8838 motor drivers, one for each of the chassis’s motors, and a powerful switching step-down regulator that can supply a continuous 2.5 A at 5 V or 3.3 V.

GPIO Interrupts

GPIO Interrupts were used in order for the robot to activate and deactivate on the press of the switches. Interrupts were necessary to use because you must wait for an interrupt before the robot could start to move. Once the switch is pressed, it will cause an interrupt, and the robot could begin to read IR sensor values and move accordingly to the steering algorithm.

Analog to Digital Conversion (ADC)

Analog to Digital conversion is required in order to read values from the IR sensors. Analog to Digital conversion is the process of converting an analog signal into a digital signal that can be processed by a digital system such as the TM4C microcontroller. Since we are using IR sensors which are analog components, we must convert the analog signals from the IR sensor’s into a digital signal in order for our IR sensors to read proper values to the microcontroller so that the robot could function as intended.

Parts List

• Breadboard

• Jumper wires

• TM4C123 microcontroller

• USB cable (for programming the microcontroller)

• Power supply (9 volts)

• 3 GP2Y0A21YK0F Sharp analog IR distance sensors

• 2 DC motors

• Pololu - Romi Chassis

• Pololu - Motor Driver and Power Distribution Board for Romi Chassis

• Pololu - Romi Encoder Pair Kit

• KeilUVision5