PA Designer Learn 2: LED and Loudness Sensor

LEDs only work if electricity passes through them in the correct direction. Insert the LED into the LED board with the positive leg of the LED in the hole marked +.

Let’s plug our loudness sensor and LED into the robot’s controller board using the cables provided. The GoPiGo3 has a number of ports we can use. In this challenge we will use the Analog Digital 1 port (AD1) for the LED and the Analog Digital 2 (AD2) port for the loudness sensor.

We are now ready to create instances of the sensor and LED classes and give them the names loudness and led for ease of reference later on. Type the following code into the code cell labelled Sensor Setup Code in the template notebook you have just uploaded.

Fill the Sensor Setup code cell:

# initialize loudness sensor object (attached to Analog Digital 2)
loudness = assistant.init_loudness_sensor("AD2")

# initialize LED object (attached to Analog Digital 1)
led = assistant.init_led("AD1")

# set the LED’s starting state to OFF
led.light_off()

The EasyGoPiGo3 class library contains init_ functions for many add-ons (e.g. init_led()). These functions create an instance and do a lot of the hard work of initializing important add-on settings for us. All we have to do is say which port we have attached the add-on to.

To test the LED, let’s write some code to flash it on and off a number of times. In the Main Code cell of our notebook, type the following code:

Main Code cell:

for i in range (1,5):
    # turn on LED at maximum brightness
    led.light_max() 
    time.sleep(0.5)

    # set LED to 30% brightness
    led.light_on(30)  
    time.sleep(0.5)

    # turn LED off
    led.light_off() 
    time.sleep(0.5)

Click on Run Selected Cell.

This demonstrates the range of functions that you can use to switch your LED on and off and adjust its brightness in a range from 0 (off) to 100 (maximum brightness). 

You might also recognize the for loop and time.sleep() instruction from Challenge 1.

Did you see the LED flash on and off? 

If not, check all of the following and re-run your code: 

If you still see no flashing LED, you could have a faulty LED. Try swapping your LED for another one.

To test the loudness sensor, let’s write some code to repeatedly take sensor readings for 10 seconds, reporting the values read as we go.

To help with this task, we have provided you with an elapsed_time() function. This measures the time difference, in seconds, between the moment that it is called and a reference time stored in a start_time variable. We need to declare this start_time variable and initialize it when we start our program by assigning the result of a time check to it.

There is an empty function in the Variable Initialization cell, called init(). Except it's not entirely empty! It has the keyword pass, which is just a placeholder for future code. Remove that pass keyword.

Within the now empty init() function , type the following code. We won’t run this code just now. Instead, we will be inserting a call to this function at the start of our Main Code cell to set everything up every time we run that cell.

Variable Initialization cell:

def init():
        # declare global variables that will be used by our program
        global start_time
    
        # perform a time-check at the start of our program
        start_time = time.time()

Now we’re ready to code up the sensor reading loop. We no longer need the code that we wrote to test the LED so

# perform all variable declaration and initialization 
init()
 
# repeat the following instructions for 10 seconds
while elapsed_time() < 10:
    print (f“Loudness = {loudness.read()}”)
    time.sleep(0.02)

Click on Run Selected Cell.

If everything is in order, you should see a stream of loudness readings displayed below the code cell (your numbers will be different):

Loudness = 171
Loudness = 126
Loudness = 314

If you don’t get any readings, run through the troubleshooting steps, noting that we are using port “AD2” for the loudness sensor, and try again.

1. Have you plugged the Loudness Sensor board into the Analog Digital 2 port?
2. Does your code initialize the Loudness Sensor using port “AD2”?
3. Are both ends of the connector cable fully inserted?

To test the loudness sensor, we repeatedly read our sensor using a WHILE loop.

Where a FOR loop repeats a set of instructions a fixed number of times, a WHILE loop repeats those instructions for as long as a condition remains true.

In the test code above, when the program has been running for 10 seconds the elapsed_time() < 10 condition will no longer be true and we will stop looping.

One line of the code does a lot of the work:

print (f"Loudness = {loudness.read()}")

loudness.read() is a loudness sensor class library function. It gives us a number that represents the loudness of the environment, as measured by the sensor. 

The print() function uses what is known as an f-string (or formatted string) as its argument. An f-string is identifiable by having an f before the quote marks. 

f-strings are different from normal strings in that they can contain variables or the results of function calls. These are marked by curly braces { }. In this case, reading from the loudness sensor {loudness.read()} is inserted directly into the string to be written into the notebook.

You are now ready to move on to the next section. What can we do with those numbers from the loudness sensor?

Find out more in the PA Designer Learn 3: Data Analysis section.

Or you may want to go back to the Personal Designer Assistant main page