{"id":225,"date":"2018-02-07T16:57:14","date_gmt":"2018-02-07T09:57:14","guid":{"rendered":"http:\/\/class.ajarnsunny.com\/?page_id=225"},"modified":"2018-02-08T02:08:18","modified_gmt":"2018-02-07T19:08:18","slug":"exercises-with-gpios-as-outputs","status":"publish","type":"page","link":"http:\/\/class.ajarnsunny.com\/?page_id=225","title":{"rendered":"Exercises with GPIOs as Outputs"},"content":{"rendered":"

Exercises with GPIOs as Outputs<\/span><\/h3>\n

Example 2.1.a<\/strong> <\/span>– using if-elif<\/strong><\/span>
\nMake the following connections (see picture<\/a>):<\/p>\n

Connect PIN 25 (GROUND)<\/strong> of the Raspberry Pi to the GND<\/strong> of the experiment board.
\nConnect PIN 22<\/strong> of the Raspberry Pi to LED 0<\/strong> of the Lower Monitor on the experiment board.<\/p>\n

Then, run the following program (file Example 2.1.A<\/a>):<\/p>\n

import RPi.GPIO as GPIO # Import library for GPIO (pin) access
\nGPIO.setmode(GPIO.BOARD) # Specify that we use the BOARD numbers (pin numbers 1-40 on the connector)
\nGPIO.setwarnings(False) # Disable the warning “This channel is already in use”<\/p>\n

# ******** PIN CONFIGURATION *************************************
\nGPIO.setup(22, GPIO.OUT) # Configure pin 22 as an output (OUT)
\n# ****************************************************************<\/p>\n

GPIO.output(22, 0) # Turn off the LED when the program starts<\/p>\n

# It could be on if a previous program left it on<\/p>\n

while True:<\/p>\n

x = input(“Enter on or off: “)
\nif x == ‘on’:<\/p>\n

GPIO.output(22, 1)<\/p>\n

elif x == ‘off’:<\/p>\n

GPIO.output(22, 0)<\/p>\n

The program asks the user to enter on<\/strong><\/em> or off<\/strong><\/em> and turns the LED on or off consequently (video<\/a>). Observe that if the user enters a string different from “on” or “off” the program does not generate any error message but simply asks the user again to “Enter on or off: “. Instead in the next Example 2.1.b (video<\/a>) the program prints the error message: “You must enter either on or off”<\/span>.<\/p>\n

Example 2.1.b<\/strong><\/span> – using if-elif-else<\/strong><\/span>
\nHere an if-elif-else structure is used (file Example 2.1.B<\/a>):<\/p>\n

import RPi.GPIO as GPIO # Import library for GPIO (pin) access
\nGPIO.setmode(GPIO.BOARD) # Specify that we use the BOARD numbers (pin numbers 1-40 on the connector)
\nGPIO.setwarnings(False) # Disable the warning “This channel is already in use”<\/p>\n

# ******** PIN CONFIGURATION *************************************
\nGPIO.setup(22, GPIO.OUT) # Configure pin 22 as an output (OUT)
\n# ****************************************************************<\/p>\n

GPIO.output(22, 0) # Turn off the LED when the program starts
\n# It could be on if a previous program left it on<\/p>\n

while True:<\/p>\n

x = input(“Enter on or off: “)
\nif x == ‘on’:<\/p>\n

GPIO.output(22, 1)<\/p>\n

elif x == ‘off’:<\/p>\n

GPIO.output(22, 0)<\/p>\n

else:<\/p>\n

print(‘ERROR: You must enter either on or off!<\/span><\/strong>‘)<\/p>\n

The program now generates a message if the user enters a string that is different from “on” or “off” as shown in this video<\/a>.<\/p>\n

Assignment 2.A<\/strong><\/span>
\nConnect LED 2, LED 1 and LED 0 to pins 26, 24 and 22 respectively (picture<\/a>) and connect pin 25 (GROUND) to GND. Write a program that implements the following (video<\/a>):<\/p>\n