Objective:
In this lesson we will use 3 Ultrasonic sensors to detect front obstacles and guide robot car to drive automatically.

Circuit Connection:
Before starting this project, you need complete hardware installation in Lesson 2 . Make sure the Lesson 2 software test is ok which means your motor installation and wiring to Raspberry Pi are all correct.

Now we can add 3 ultrasonic sensors(distance sensor) in front side. The center sensor should face straight ahead, right sensor face a 30 to 45 degree right of straight ahead direction , left sensor should face 30 to 40 degree left of straight ahead direction. Wiring connection should be as per following graph:

Sensor Pin Pi GPIO(BCM)
Right Sensor TRIG 18
Right Sensor ECHO 23
Center Sensor TRIG 24
Center Sensor ECHO 25
Left Sensor TRIG 16
Left Sensor ECHO 20

Software Installation:
1)Use putty (or ssh in Linux/iOS terminal)  to connect your Raspberry Pi and then type following command:

wget  http://osoyoo.com/driver/obstacle.tar.gz

tar -zxvf obstacle.tar.gz

2)Put your robot car onto ground, turn on the car again, now use putty or ssh to connect to Raspberry Pi again. Then type following command in terminal:

cd obstacle

python autodrive.py

You will see your car is automatically moving and avoiding front obstacles. You will see obstacle situation and car action from your Raspberry Pi terminal . The obstacle status is a string. For example 001 means right