Interesting Basic Experiments with Raspberry Pi Pico

Last week we gave away Raspberry Pi Pico, and today we have prepared some experimental routines for everyone. This includes several basic experiments with code and results.

▌01 PI Pico Experiment Board

The Raspberry Pi Pico Development Board Basic Test^[1] provides the basic setup for the PI Pico development board. By installing the Thonny development environment^[2], it is convenient to perform initial development on the Pi Pico.

Interesting Basic Experiments with Raspberry Pi Pico — ▲ Front and back of the Pi Pico circuit board

Below, based on the Raspberry Pi Pico Python SDK^[3], we will test some basic modules of the PI Pico.

For the pin configuration of Pi Pico, please refer to the Pi Pico datasheet^[4] for the pin diagram definition:

▌02 Basic Tests

1. Flash LED on Board

from machine                import Pin,Timer
from time                   import sleep_us

led = Pin(25, Pin.OUT)
tim = Timer()

print("Flash LED.")

def tick(timer):
    global led
    led.toggle()

tim.init(freq=2, mode=Timer.PERIODIC, callback=tick)

▲ Experimental circuit board

2. UART

(1) Test Program

from machine                import UART,Pin,Timer
from time                   import sleep_us

uart = UART(0, baudrate=115200, tx=Pin(0), rx=Pin(1), bits=8, parity=None, stop=1)
led = Pin(25, Pin.OUT)

tim = Timer()

print("Send UART.")

def tick(timer):
    global uart, led

    led.toggle()
    uart.write(b'\x55')

tim.init(freq=10, mode=Timer.PERIODIC, callback=tick)

3. ADC

Read the internal temperature of the chip through ADC channel 4. During this process, use your hand to touch the surface of the Pi Pico to heat it, or use alcohol to spray the surface of the chip for cooling.

import machine
import utime

sensor_temp = machine.ADC(4)
conversion_factor = 3.3/(65535)

while True:
    read = sensor_temp.read_u16() * conversion_factor

    temperature = 27 - (read - 0.706) / 0.001721
    print(temperature)
    utime.sleep(2)

4. PWM

(1) PWM Driving LED

The waveform controlling the onboard LED operates on PWM.

from machine                import Pin,PWM
import time

pwm = PWM(Pin(25))

pwm.freq(1000)

duty = 0
direction = 1

for _ in range(16*255):
    duty += direction

    if duty > 255:
        duty = 255
        direction = -1
    elif duty < 0:
        duty = 0
        direction = 1

    pwm.duty_u16(duty*duty)
    time.sleep(0.001)

PWM is software PWM, and it can be set on any pin. Preliminary tests have been conducted on Pin0, 15, 16, etc. All have similar waveforms.

(2) PWM Driving Servo

The servo uses a frequency of 50Hz, with a pulse width of 1.0 ~ 2.0ms as the control signal. Below is the output control pulse generated for the basic middle position of the servo.

from machine                import Pin,PWM
import time

pwm = PWM(Pin(15))

pwm.freq(50)
pwm.duty_u16(4915)

The servo has three wires:

Brown: GND
Red: +4.5 ~ +6V
Yellow: Command pulse signal

Calculate the Duty_16 formula as follows:

The relationship between the corresponding pulse width and duty_u16:

from machine                import Pin,PWM
import time

pwm = PWM(Pin(16))

pwm.freq(50)

for _ in range(100):
    pwm.duty_u16(3276)
    print("Out pulse width : 1ms")
    time.sleep(1)

    print("Out pulse with : 2ms.")
    pwm.duty_u16(6553)
    time.sleep(1)

(3) PWM+ADC Experiment

Using a potentiometer to introduce a changing voltage into ADC(0), the microcontroller obtains the corresponding ADC value, and changes the PWM output to proportionally vary the output time width from 1ms to 2ms.

You can see that the servo’s output angle changes with the potentiometer.

from machine                import Pin,PWM
import time

pwm = PWM(Pin(16))

pwm.freq(50)

control = machine.ADC(0)

for _ in range(1000):
    adc = control.read_u16()
    duty = int(adc * (6553-3276)/0xffff) + 3276
    pwm.duty_u16(duty)
    time.sleep(0.1)

5. Interrupt IRQ

Using the falling edge of pin PIN2 to generate an interrupt. The example program is as follows:

from machine                import Pin

p2 = Pin(2, Pin.IN, Pin.PULL_UP)

p2.irq(lambda pin:print("IRQ with flag:",
        pin.irq().flags()),
        Pin.IRQ_FALLING)

Using a jumper to ground PIN2. Each time it is grounded, an interrupt is triggered.

03▌Conclusion

Through several basic Pi Pico experiments, preliminary application examples of this module have been provided.

Last week’s event, we gave away some Raspberry Pi Pico, come and see the lucky draw!

References

[1] Raspberry Pi Pico Development Board Basic Test:

https://zhuoqing.blog.csdn.net/article/details/114037888

[2] Installing Thonny Development Environment:

https://zhuoqing.blog.csdn.net/article/details/114064833[3] Raspberry Pi Pico Python SDK:

https://datasheets.raspberrypi.org/pico/raspberry-pi-pico-python-sdk.pdf[4] Pi Pico Datasheet:

https://datasheets.raspberrypi.org/pico/pico-datasheet.pdf[5] Pi Pico Official Website:

https://www.raspberrypi.org/documentation/rp2040/getting-started/

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