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Blink LED

Check out the Wokwi Prototype.

Don't forget to check the Pi Pico Diagram as you go:

Blink the onboard LED

from machine import Pin
from time import sleep

# Wait for USB to become ready
sleep(0.1)

#store desired output pin in a variable
led_pin = 25

#configure GPIO Pin as an output pin and create and led object for Pin 
led = Pin(led_pin, Pin.OUT)

while True:
   led.value(True)  #turn on the LED
   sleep(1)   #wait for one second
   led.value(False)  #turn off the LED
   sleep(1)   #wait for one second

Note

The Onboard LED is connected to GPIO Pin 25 and useful for debugging events.

Unit Testing

  1. The onboard LED next to the USB connection should toggle on/off every second.

Connect and blink an external LED

LED pin Pi Pico pin
Long (anode) GP15 (20)
Short (cathode) Ground (GND)

Note

Students can build using physical components or prototype using this Template Wokwi Project.

from machine import Pin
from time import sleep

# Wait for USB to become ready
sleep(0.1)

#store desired output pin in a variable
led_pin = 25
led2_pin = 15

#configure GPIO Pin as an output pin and create and led object for Pin 
led = Pin(led_pin, Pin.OUT)
led2 = Pin(led2_pin, Pin.OUT)

while True:
   led.value(True)  #turn on the LED
   led2.value(False)  #turn off the LED2
   sleep(1)   #wait for one second
   led.value(False)  #turn off the LED
   led2.value(True)  #turn on the LED2
   sleep(1)   #wait for one second

Unit Testing

  1. The onboard LED and external LED next to the USB connection should alternatively toggle on/off every second.

How to calculate resistance

A resistor is required to protect the LED from over current. To calculate the resistor value for an LED connected to a 3.3V source, you need to use Ohm's Law $(V = IR)$, but first, determine the LED's forward voltage and desired forward current. The formula is R = (V_source - V_forward) / I_forward.

Here's how to do it:

  1. Find the LED's forward voltage (V_forward): This is the voltage drop across the LED when it's turned on. Typical values are around 2V for red/green LEDs and 3V for blue/white LEDs. If you don't know the exact forward voltage, check the LED's datasheet or consult a reference chart.
  2. Determine the desired forward current (I_forward): This is the current you want the LED to draw. A common range is 5mA to 20mA. You can find this information in the LED's datasheet or use a typical value.
  3. Calculate the resistance (R): Plug the values into the formula: R = (V_source - V_forward) / I_forward Example: Let's assume you have a 3.3V source, an LED with a forward voltage of 2V, and you want a forward current of 10mA (0.01A).
R = (3.3V - 2V) / 0.01A
R = 1.3V / 0.01A
R = 130 Ohms

You would then choose a resistor with a value close to 130 Ohms.