Urbanite: Parking aid system
Urbanite Project

This project demonstrates how the project Urbanite works using an ultrasound transceiver to measure the distance to an object in a parking aid system mounted on a car. It uses a finite state machine (FSM) to control the ultrasound sensor, a display (RGB LED) to show the distance, and a button to interact with the system.

This project is intended to be used with the MatrixMCU toolkit. The toolkit is available at GitHub: MatrixMCU.

Click on the image to see the video showing the Urbanite demo for Nucleo STM32:

Urbanite Demo

Version 1

In Version 1, the system works with the user button only. The user button is connected to the pin PC13. The code uses the EXTI13 interrupt to detect the button press.

Parameter Value
Pin PC13
Mode Input
Pull up/ down No push no pull
EXTI EXTI13
ISR EXTI15_10_IRQHandler
Priority 1
Subpriority 0
Debounce time 100-200 ms

You can start from the HW dependent part of Version 1.

This is the FSM of the button:

FSM of the button

Version 2

In Version 2, the system adds the ultrasonic transceiver to measure the distance to an object. The trigger pin is connected to the pin PB0, and the echo pin is connected to the pin PA1. The code uses the TIM2, TIM3 and TIM5 timers to control the ultrasonic transceiver.

To measure the distance in centimeters with a timer resolution of 1 microseconds, we can say that 1 cm is equivalent to 58.3 microseconds. The speed of sound is 343 m/s at 20ºC. The ultrasonic transceiver is the HC-SR04.

The characteristics and connections of the ultrasonic transceiver HC-SR04 are shown in the table below:

Parameter Value
Power supply 5 V
Current 15 mA
Angle of aperture 15º
Frequency 40 kHz
Measurement range 2 cm to 400 cm
Pins PB0 (Trigger) and PA1 (Echo)
Mode Output (Trigger) and alternative (Echo)
Pull up/ down No pull
Timer TIM3 (Trigger) and TIM2 (Echo)
Channel (see the Alternate Function table in the datasheet)

The system uses 3 timers: (i) one to control the duration of the trigger signal, (ii) another to measure the echo time, and (iii) another to measure the timeout between consecutive measurements that we want to make. The timing diagram of the measurements is shown in the figure below.

To generate the trigger signal, we will activate (1 logical) the trigger pin for at least 10 microseconds. To control the duration of this signal, we will configure the timer TIM3 as shown in the table below.

Parameter Value
Timer TIM3
Prescaler (to be calculated for PORT_PARKING_SENSOR_TRIGGER_UP_US)
Period (to be calculated for PORT_PARKING_SENSOR_TRIGGER_UP_US)
ISR TIM3_IRQHandler()
Priority 4
Subpriority 0

To measure the echo time, we will configure the timer TIM2 in input capture mode, which will capture the value of the counter at the moment the echo signal is activated and deactivated.

Parameter Value
Timer TIM2
Prescaler (to be calculated for 1 microseconds)
Period (to be calculated for 1 microseconds)
ISR TIM2_IRQHandler()
Priority 3
Subpriority 0

The timer that controls the timeout between consecutive measurements is TIM5. The characteristics of this timer are shown in the table below. The FSM will give a value every PORT_PARKING_SENSOR_TIMEOUT_MS milliseconds.

Parameter Value
Timer TIM5
Prescaler (to be calculated for PORT_PARKING_SENSOR_TIMEOUT_MS)
Period (to be calculated for PORT_PARKING_SENSOR_TIMEOUT_MS)
ISR TIM5_IRQHandler()
Priority 5
Subpriority 0

You can start from the HW dependent part of Version 2.

This is the FSM of the ultrasonic transceiver:

FSM of the ultrasonic transceiver

Version 3

In Version 3, the system adds the display, which is an RGB LED. The RGB LED is connected to the pins PB6 (red), PB8 (green), and PB9 (blue). The code uses the TIM4 timer to control the frequency of the PWM signal for each color. The RGB LED will show the distance to the object detected. The characteristics of the display are shown in the table below.

Parameter Value
Pin LED red PB6
Pin LED green PB8
Pin LED blue PB9
Mode Alternative
Pull up/ down No pull
Timer TIM4
Channel LED red (see the Alternate Function table in the datasheet)
Channel LED green (see the Alternate Function table in the datasheet)
Channel LED blue (see the Alternate Function table in the datasheet)
PWM mode PWM mode 1
Prescaler (to be calculated for a frequency of 50 Hz)
Period (to be calculated for a frequency of 50 Hz)
Duty cycle LED red (variable, depends on the color to show)
Duty cycle LED green (variable, depends on the color to show)
Duty cycle LED blue (variable, depends on the color to show)

You have a list full of colors in www.downtownuplighting.com although not all can be shown on an RGB LED.

The following table shows the duty cycle values for each color in function of the distance. Be careful, these values are not the ones that you put in the **CCRx register!** They depend on the PORT_DISPLAY_RGB_MAX_VALUE. The values are shown in the table below.

Distance Color LED red LED green LED blue
$[0-25]$ cm Red (danger) 100% 0% 0%
$(25-50]$ cm Yellow (warning) 37% 37% 0%
$(50-150]$ cm Green (no~problem) 0% 100% 0%
$(150-175]$ cm Turquoise (info) 10% 35% 32%
$(175-200]$ cm Blue (OK) 0% 0% 100%
Other distances Off (inactive) 0% 0% 0%

You can start from the HW dependent part of Version 3.

  • Here you can find the files needed for the control of the display: Display.
  • Here you can find the test files for Version 3: V3 test files

This is the FSM of the display:

FSM of the display

Version 4

In Version 4 the system completes its FSM to interact with the user button, the ultrasonic transceiver, and the display. The system will show the distance to the object detected in the display.

There are no files for Version 4, and you have to create them from scratch. You can use the files of the previous versions as a reference.

Check the HW dependent part of Version 4.

This is the FSM of the system:

FSM of the system

Version 5

In Version 5 the user adds its own functions to the system. Check the manual of the system to know how to add your own functions.

Getting Started

Download this project and place it in the projects folder of the MatrixMCU toolkit.

Prerequisites

Be sure that you fulfill the prerequisites of the MatrixMCU toolkit and it is up to date.

Document your code

Watch this video to better understand how to document your code with Doxygen:

Link to Doxygen tutorial

Authors

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

  • Iván Ferández Martín, Sergio Esteban Romero, and all professors of the SDG2 subject.

References