Welcome to Raspbot repository

1. Learning target

In this course, we will learn how to use ultrasonic module and infrared obstacle avoidance sensor completes obstacle avoidance experiment.

2. Principle of experimental

About ultrasonic module:

The ultrasonic module is a sensor that uses ultrasonic characteristics to detect the distance. It has two ultrasonic probes for transmitting and receiving ultrasonic waves. The range of measurement is 3-450 cm.

(1) You need to input a high level signal of at least 10us to the Trig pin to trigger the ranging function of the ultrasonic module.                     

(2) After the ranging function is triggered, the module will automatically send out 8 ultrasonic pulses with 40 kHz and automatically detect whether there is a signal return. This step is done internally by the module.

(3)  When the module detects an echo signal, the ECHO pin will output a high level. The high level duration is the time from when the ultrasonic wave is sent to when it returns. You can calculate the distance by using the time function to calculate the high level duration. 

Formula: Distance = High level duration * Speed of sound(340M/S)/2.

About Infrared obstacle avoidance sensor:

There are two sets of infrared obstacle avoidance sensors on both sides of the trolley.

Their transmitting tube emits infrared light from the luminous tube, and the receiving tube receives the infrared light reflected by objects in front of them to determine whether there are obstacles in front.

When there is an obstacle in front, the infrared sensor pin is low and the indicator light is on;

When there are five obstacles in the front, the infrared sensor pin is high and the indicator light is off;

Because the infrared pair tube is turned on for a long time, it will heat up and shorten its service life, so we specially designed a switch for it, which needs to be turned on before using infrared obstacle avoidance.

For the Raspbot car, we use 4 TT DC gear motors. They are driven by the AT8236 chip. The driver chip is not directly connected to the Raspberry Pi pins.

Raspberry Pi communicates with STM8 MUC through IIC, and then STM8 MCU drives AT8236 chip to drive the motor.

3. Coding method

In this course, we use BOARD coding method.

According to the hardware interface manual, we see that the ultrasonic Echo and Trig pins are connected to the 18 and 16 pin of the Raspberry Pi board. 

The left and right infrared obstacle avoidance sensors and switches are respectively connected to pins 21, 19, and 22 of the Raspberry Pi board.

STM8 is connected to SDA.1, SCL.1 on the Raspberry Pi board.

We have provided a library text dedicated to driving motors and servos --YB_Pcb_Car.py.

It is located in the same directory as the motor driver.

The pin comparison table of Raspberry Pi as shown below.

4. About code

Path: /home/pi/Yahboom_project/Raspbot/2.Hardware Control course/6.Ultrasonic+IR avoid/Ultrasonic+IR avoid.ipynb

1) Import time, GPIO and YB_Pcb_Car library

2)Set the GPIO code and the mode of the ultrasonic pin, and define the car class is used to drive motors or servos.

Set the infrared sensor switch pin is high level to enable infrared obstacle avoidance function.

3) Define the ultrasonic ranging function

We need to set a high level signal of at least 10us to the TRIG pin of the ultrasonic module to trigger the module's ranging function.

4) Define the ultrasonic ranging optimization program to optimize the test results.

5)Define the avoid function to complete the ultrasonic +IR obstacle avoidance function of the car.

6) Call the obstacle avoidance function in loop to complete the obstacle avoidance experiment.

When we click the stop button, we exit the loop, stop the car, and clear the car class and GPIO.

5. Running code

Click the button shown in the figure below to run the program on the Jupyter Lab interface

6. Experimental phenomenon

After the program runs, we can see that the car will move forward, and it will avoid obstacles when it encounters obstacles in front of it.