System Design Documentation

[NicoSeia]

Milestone Description:

• Objective: Outline the design of the embedded system to ensure that all team members understand the structure and functionality.
• Deliverables:
  • Block diagrams or flowcharts representing the system architecture.
  • State diagrams or flow diagrams for critical functions or states.
  • Define the main modules, their purpose, and how they interact.
  • Describe the communication between different components, especially if peripherals like ADC, DAC, GPIO, or other sensors are used.

In this issue:

• We will describe our system, its modules and how the communication between the different components is handled through software.
• Everything should be explained in a user-friendly way.

[NicoSeia]

Our Modules:

Main Program

It controls the overall flow of the processes done by the embedded system we are using, the stm32f103T8c, and acts as the entry point of the system.

• Configures and initializes the microcontroller.
• Initializes the 16x2 LCD display, the HCSR04 ultrasonic sensor, the Motor motor control and the Speedometer.
• Obtains and displays the distance measured by the sensor on the LCD display.
• It calls the functions of the other modules to receive data from the sensors and display information on the screen.
• Acts as the mediator that receives data from the ultrasonic sensor and sends it to the LCD module for display.
• Best case scenario: the system manages module communication through a tasks implemented in a FreeRTOS enviroment.
  • Minimum Viable Product: the system does this through interruptions.

---

lcd.c

Controls the LCD display via I2C using a PCF8574 pin expander using these functions:

• lcd_init: Initialises the display in 4-bit mode and configures the I2C protocol.
• lcd_print_string: Displays a string on the screen, useful for displaying distance information or status messages.
• lcd_clear: Clears the contents of the display and repositions the cursor in the upper left corner.
• lcd_set_cursor: Controls the position on the screen for writing content at specific locations.

We use I2C to communicate with the PCF8574 I2C I/O Expander, which in turn controls the LCD. This module receives the data to be displayed from the main.

---

hc_sr04

Drives the HC-SR04 ultrasonic sensor to measure distances.

• hcsr04_init: Configures the trigger (TRIG_PIN) and echo (ECHO_PIN) pins, and sets the timers needed to measure the time of flight of the ultrasonic pulse.
• hcsr04_trigger: Sends a 10-microsecond pulse to the TRIG_PIN, which initiates the measurement on the sensor.
• hcsr04_get_distance: Measures the time it takes to receive the return pulse at the ECHO_PIN, and calculates the distance based on that time.

Uses GPIO and timers to control the TRIG and ECHO pins and measure the flight time. The hcsr04_get_distance function returns the calculated distance to main.

---

Motor Control

Control the motor using PWM. This module allows you to initialise the GPIO and timer to generate a PWM signal, adjust the motor power by varying the PWM duty cycle, and enable/disable the motor output.

• motor_init(): Initialises the GPIO and timer for the PWM.
• motor_set_power(uint8_t percentage): Sets the motor power to the specified percentage.
• motor_enable() and motor_disable(): Enables or disables the motor.

---

PID Controller

Implement a PID controller to adjust the motor power based on a measured value (such as speed or position) and a reference value.

• pid_init(PID_Controller *pid): Initialises the PID structure with the desired gains and reference.
• pid_update(PID_Controller *pid, float measured_value): Calculates the PID output value, adjusting the motor power.
• pid_setpoint(PID_Controller *pid, float setpoint): Sets the reference value for the controller.

---

Speedometer

Measure the motor speed in RPM using a sensor or pulse counter.

• speedometer_init(): Initialises the speed sensor.
• speedometer_getRPM(): Calculates and returns the current motor speed in RPM.

---

Setpoint

Module in charge of reading the value of a potentiometer through the ADC and DMA in the microcontroller.

• It allows to obtain the potentiometer value (pot_get_value) to use it in control settings, such as setpoint or PID gain adjustment.

---

Button

This module manages the button inputs (START/STOP) to control the activation and deactivation of the motor, as well as object detection

• It configures GPIO pins for the STOP_BUTTON and CONTROL_BUTTON buttons and enables interrupts (EXTI10 and EXTI11) with debounce functions. The interrupts set flags (object_flag and stop_flag) that other parts of the system check to respond to button events.
• Communicates button events to the host system via object_flag and stop_flag. The exti15_10_isr function disables the engine and displays ‘STOPPED!’ on the screen when stop_flag is triggered.

---

Update

It controls the periodic update logic for the system, including PID control, measurement acquisition, and LCD data display.

• The sys_tick_handler function is the SysTick interrupt handler, which performs periodic system operations such as PID tuning, distance measurement collection, and on-screen display control. It controls the frequency of these operations with various response counters (response__pid_count, response__measurement_count, etc.).
• Calls functions to handle motor speed update (via the PID module) and display of speed or height as a function of object_flag and stop_flag.

[iledesma08]

Communication between different components

Each module in the system has its own communication with the peripherals and sensors of the STM32 microcontroller, optimising the use of resources through I2C, GPIOs, timers, and ADCs. Each of these communications and how they interact with each other is detailed below:

Communication with the LCD via I2C:

• The lcd.c module uses the I2C protocol to send data to the PCF8574 pin expander, which then controls the LCD display. The PCF8574 allows commands and data to be sent to the LCD using only two pins (SDA and SCL), which saves GPIOs on the STM32.

---

Distance measurement with the HC-SR04 using GPIOs and timers

• The HC-SR04 ultrasonic sensor measures distance by detecting echoes. It uses two digital pins (TRIG_PIN and ECHO_PIN) connected to GPIOs on the STM32.
• The STM32 sends a trigger pulse to TRIG_PIN.
• When the sensor detects an object, it sends a pulse to ECHO_PIN, the duration of which is measured using a timer.

---

Motor control by PWM and setpoint reading with ADC:

Motor Control using PWM

• The motor control uses PWM to adjust the speed by duty cycle, which determines the power the motor receives.
• The motor_control module uses a timer configured in PWM mode to control the duty cycle and thus the speed of the motor.
• The PID controller adjusts the duty cycle according to the calculated error between the desired speed (setpoint) and the actual speed (encoder feedback).

Setpoint reading by the ADC

• The ADC (Analogue to Digital Converter) reads the value of the potentiometer that the user uses to set the desired speed or setpoint.
• The analogue signal from the potentiometer is converted into a digital value, which the pot module uses to define the setpoint.
• The potentiometer value becomes the setpoint for the PID, which adjusts the motor control in real time based on this reference.

---

Encoder Feedback for Speed Measurement

• Optionally, the system can include an encoder to provide feedback on motor speed.
• The encoder generates pulses that are read by a timer configured to count pulses, allowing the speed to be calculated in revolutions per minute (RPM) or radians per second (rad/s).
• The speed measured with the encoder is used in the PID calculation, providing feedback data to reduce error and make more precise adjustments to the motor control.