4.1: Sensors Introduction

Goals:

By the end of this lesson, I will be able to:

1. Identify the importance of sensors to drone flight
2. Identify different types of sensors and their uses
3. Explain why calibration of sensors is important
4. Describe the types of functions that sensors use
5. Explain why we use objects in programs to represent sensors
6. Identify different measurements that sensor will take based on the sensor type
7. Write a program to do a pre-flight check of all sensors prior to takeoff
8. Identify sensors used on drones and robots in industry and their purpose
9. Explain what an object is in programming and why they are useful

Steps to Success:

1. What is a Sensor?
2. Sensor Values
3. Sensors as Objects
4. Pre-Flight Sensor Check
5. Challenge: Sensor Research

Sensors are electronic devices that turn information about their environment into a value that can be used in a program. Like many other input devices, sensors send digital signals to a computer which it can then use to make decisions. They are often used in electronic devices to make sense of the outside world because they are very good at turning Analog information into Digital information. Analog information or data is simply data that has constantly change values.

Take a moment and think about a cell phone. In what ways do you interact with it? What tools or apps make it useful to you? Based on your responses, make a list of the types of sensors your phone may have.

Once you have completed your list, see if you have any of the following listed:

• GPS
• Gyroscope (for screen rotation and phone movement)
• Light Sensor
• Camera
• Microphone
• Touch Screen

These sensors make our phones valuable to their users because they become more interactive and intuitive (they understand their environment). As we write programs with our CoDrone Mini to make it more interactive with its environment, there are generally four steps that we will use:

1. The sensor will gather environmental data (often analog)
2. The sensor will convert that data into a digital value or signal
3. We will store the value in a variable
4. We will implement the variable into our program

To explore this concept a little further, let’s take a look at an example of how GPS works in cell phones:

As we mentioned, there are a wide variety of sensors that are used in devices. However, they all send different values based on what they are measuring. Look at the list below and try to think of what values these sensors might give you:

1. Temperature Sensor – Answer: Degrees in Fahrenheit
2. Microphone
3. Camera
4. Touch Screen
5. Gyroscope
6. Battery indicator
7. Barometer
8. Light Sensor

Since most sensors are simply reporting values, we typically see that the commands to get these values use the word get.

Objects  are an abstraction tool used in many programming languages to group functions or components together. This can allow us to represent physical objects like a sensor in a digital program.

Objects have functions and properties:

Getter: retrieves a value stored in the object. Sensors use getter functions to report the values they are reading. The sensor stores and then reports a value when its getter function(s) are called.

Setter: changes something about the object. Sensors typically use setter functions to reset or calibrate the sensor.

Properties: These are not a function, but are values that describe the object, such as the type of sensor or its current state.

One of the great benefits of objects is that they can be replicated multiple times, each with its own unique properties. This is one of the reasons we like to represent objects as sensors. If you image a very complex drone, it may have multiple sensors of the same type which help it navigate. For example, it might have 6 ultrasonic (distance-detecting) sensors that are all the same type that help it navigate an environment without running into things. How then, do we differentiate between the different sensors? Objects! Because objects can be replicated and still keep the same functions, we could create 6 different ultrasonic sensor objects and use the same functions to read their values, change their settings, etc…

Often times, our drone may crash, have low battery, or our program may cause issues with a sensor. When a sensor is not reporting correct values, we say that it is out of calibration. Most sensors have the ability to calibrate, or adjust, its values to more closely represent reality. We have already calibrated the drone in the past when we learned how to use the trim() function. Luckily for us, the CoDrone mini self-calibrates before each launch.

Now that we know our sensors are calibrated, let’s do a pre-flight systems check. Commercial pilots will often check their various sensors to make sure they are reading correct values before taking off. Put your drone on a flat table and create the following code:

import CoDrone_mini

drone = CoDrone_mini.CoDrone()
drone.pair()

print("Temperature is: " + drone.get_drone_temp)
print("Pressure is: " + drone.get_pressure)
print("Battery is: " + drone.get_battery_percentage)
print("Angle is: " + drone.get_angle)

drone.close()

Once you have run the code, what values did you get?

To figure out what each of these values means, do the following and then run the code above again:

1. Have the drone takeoff and then land.
2. Turn the drone on its side.
3. Put the drone on the floor.
4. Have the drone takeoff, hover for 5 seconds, and then land.

As we move through the lessons in this module, you will learn what each of these values means to our drone and how to use these sensors to make more advanced programs.

For this challenge, identify at least 3 sensors used in robotics and drones. For each, explain the following:

• What type of value the sensor reports
• How this value is manipulated or converted
• How the sensor can be used to impact the robot or drone’s flight movements

You are not allowed to use the CoDrone Mini as an example, you must locate other drones and robots used in a professional environment.