cca_robotics_2021

Course materials for CCA high-school robotics class, academic year 2021-22.

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Project maintained by buffetboy2001 Hosted on GitHub Pages — Theme by mattgraham

Sense an Obstacle

Module Goal: connect your obstacle sensor and write Python code to use it!

Acknowledgement: images and python code snippets in this module are copied directly from the this excellent PiHut tutorial.

What You Need

• 8 wires (select four unique colors, if possible)
• the obstacle sensor
• two resistors (ask Mr. Bowman)
• the breadboard

Assembly

Examine the obstacle sensor’s four connections. It looks like this:

Connect these wires:

• Connect the VCC wire to pin 2 on the Raspberry Pi
• Connect the TRIG wire to pin 23 on the Raspberry Pi

Now for the breadboard connections. First, add your resistors like this:

Next:

• Connect the GND wire to any GND on the Raspberry Pi
  • connect the other end to the breadboared like in the picture
• Connect the ECHO wire to pin 24 on the Raspberry Pi
  • connect the other end to the breadboard like in the picture

This sensor can only work with some code to interpret the signals.

Python Code

import RPi.GPIO as GPIO
import time
 
#GPIO Mode (BOARD / BCM)
GPIO.setmode(GPIO.BCM)
 
#set GPIO Pins
GPIO_TRIGGER = 23
GPIO_ECHO = 24
 
#set GPIO direction (IN / OUT)
GPIO.setup(GPIO_TRIGGER, GPIO.OUT)
GPIO.setup(GPIO_ECHO, GPIO.IN)
 
def distance():
    # set Trigger to LOW, then HIGH
    GPIO.output(GPIO_TRIGGER, False)
    time.sleep(1)
    GPIO.output(GPIO_TRIGGER, True)
 
    # set Trigger after 0.01ms to LOW
    time.sleep(0.00001)
    GPIO.output(GPIO_TRIGGER, False)
 
    StartTime = time.time()
    print(f'StartTime:{StartTime}')
    StopTime = time.time()
    print(f'StopTime:{StopTime}')
 
    # save StartTime
    while GPIO.input(GPIO_ECHO) == 0:
        pass
    StartTime = time.time()
 
    # save time of arrival
    print('looking for low while high')
    while GPIO.input(GPIO_ECHO) == 1:
        pass
    StopTime = time.time()
    print('echo went low and exited')
 
    # time difference between start and arrival
    TimeElapsed = StopTime - StartTime
    # multiply with the sonic speed (34300 cm/s)
    # and divide by 2, because there and back
    distance = (TimeElapsed * 34300) / 2
 
    return distance
 
if __name__ == '__main__':
    try:
        while True:
            dist = distance()
            print ("Measured Distance = %.1f cm" % dist)
            time.sleep(1)
 
        # Reset by pressing CTRL + C
    except KeyboardInterrupt:
        print("Measurement stopped by User")
        GPIO.cleanup()

Try It Out

Place your sensor directly in front of a solid object that is close-by (1 foot away). Run the script and observe the output.

Hopefully, you’ve got sensor readings telling you how far away (approximately) the object is.

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Module Complete