1.9: IR Sensors

Step 1

IR Sensors

Infrared (IR for short) is a form of electromagnetic radiation that is not visible with the human eye. It’s also a form of energy. However, as scary as the name sounds, not all electromagnetic radiation is dangerous. There is a small portion of it that we can see, meaning this is visible light! The different colors that we see depend on the various wavelengths. As the wavelengths get longer, the colors become less visible to humans. However, special sensors can detect these waves. You will use the IR sensors on Zumi to detect objects that are covering the sensors.

Step 2

Zumi IR sensors

Zumi is equipped with 6 IR sensors: two in the front, two in the back, and two on the bottom. They all have an index so that it’s easier to read their data:

IR 0 = front right
IR 1 = bottom right
IR 2 = back right
IR 3 = bottom left
IR 4 = back left
IR 5 = front left

Step 3

Display IR data on the screen

You are going to display the IR data on Zumi’s screen. To get IR data you’ll need a Zumi object, and to display on the screen you need to create a Screen object.

Import libraries

In [ ]:

from zumi.zumi import Zumi
from zumi.util.screen import Screen
import time

zumi = Zumi()
screen = Screen()

What does the data mean?

IR sensors work by emitting an infrared pulse and measuring the infrared light that returns after it bounces off an object. This number will be between 0 and 255. A lower number indicates that something in the vicinity is reflecting the IR light back to the sensor.

Run each cell and watch the numbers on the screen change as you cover the sensors. The code will use a for loop to take 50 readings.

Front IR sensors

In [ ]:

for i in range(0,50):
    ir_readings = zumi.get_all_IR_data()
    front_right_ir = ir_readings[0]
    front_left_ir = ir_readings[5]
    
    message = "    IR readings        "
    message = message + str(front_right_ir) + ", " + str(front_left_ir)
    screen.draw_text(message)
    time.sleep(0.1)
screen.draw_text_center("Done!")

Back IR sensors

In [ ]:

for i in range(0,50):
    ir_readings = zumi.get_all_IR_data()
    back_right_ir = ir_readings[2]
    back_left_ir = ir_readings[4]
    
    message = "    IR readings        "
    message = message + str(back_right_ir) + ", " + str(back_left_ir)
    screen.draw_text(message)
    time.sleep(0.1)
screen.draw_text_center("Done!")

Bottom IR sensors

Bottom IR sensors are great for line following or detection. Use the Bottom IR worksheet to test values between light and dark.

In [ ]:

for i in range(0,50):
    ir_readings = zumi.get_all_IR_data()
    bottom_right_ir = ir_readings[1]
    bottom_left_ir = ir_readings[3]
    
    message = "    IR readings        "
    message = message + str(bottom_right_ir) + ", " + str(bottom_left_ir)
    screen.draw_text(message)
    time.sleep(0.1)
screen.draw_text_center("Done!")

Step 4

Lists

You may notice something about the IR data that you haven’t seen yet. In all of the examples, we use a function called get_all_IR_data(). However, there are six IR sensors that each have a value. How can they all be in the same variable? All this data is actually stored in a list. In Python, lists can be used to store and organize data of the same type without creating multiple variables.

Accessing values

When you call zumi.get_all_IR_data(), the program requests all the sensor data and saves them in a list with, you guessed it, six items. In this example, the list name is ir_readings. Unlike a shopping list that is usually vertical, a list in Python is written horizontally and enclosed in [brackets]. The next cell will take a reading and print out the values.

In [ ]:

ir_readings = zumi.get_all_IR_data()
print(ir_readings)

Printing the list name will print all of the values, but what if you just want to check one or two values? You can access the data, or each element, by its index. The index is like the home address of where it lives in the list. As with for loops, Python lists start at 0. Take this list for example. What is value of the first element? What about the last?

Below is an example of accessing the first element at index 0. Practice printing all of the values. Make sure you save the IR values in a variable with a descriptive name! When your programs start getting more complicated, you don’t want to forget which value corresponds to what sensor.

In [ ]:

ir_readings = zumi.get_all_IR_data()
front_right_ir = ir_readings[0]
print(front_right_ir)

This lesson uses:

Grade level:

Approx. time required:

IR Sensors

Zumi IR sensors

Display IR data on the screen

Import libraries

What does the data mean?

Front IR sensors

Back IR sensors

Bottom IR sensors

Lists

Accessing values