How can I get a Raspberry Pi pico to communicate with a PC / external devices?

For example when I give 5 to the code, I want to turn on the LED in our RPi pico (connected to a PC via a cable).

#This code will run in my computer (test.py)

x=int(input("Number?"))
if (x==5):
    #turn on raspberry pi pico led

The code of the RPi pico:

#This code will run in my rpi pico (pico.py)

from machine import Pin
led = Pin(25, Pin.OUT)

led.value(1)

Or vice versa (doing something in the code on the computer with the code in the RPi pico).

How can I call/get a variable in the PC to the RPi pico?

Note: I am writing code with OpenCV Python and I want to process the data from my computer's camera on my computer. I want the RPi pico to react according to the processed data.

Solution

A simple method of communicating between the host and the Pico is to use the serial port. I have a rp2040-zero, which presents itself to the host as /dev/ttyACM0. If I use code like this on the rp2040:

import sys
import machine

led = machine.Pin(24, machine.Pin.OUT)

def led_on():
    led(1)

def led_off():
    led(0)


while True:
    # read a command from the host
    v = sys.stdin.readline().strip()

    # perform the requested action
    if v.lower() == "on":
        led_on()
    elif v.lower() == "off":
        led_off()

Then I can run this on the host to blink the LED:

import serial
import time

# open a serial connection
s = serial.Serial("/dev/ttyACM0", 115200)

# blink the led
while True:
    s.write(b"on\n")
    time.sleep(1)
    s.write(b"off\n")
    time.sleep(1)

This is obviously just one-way communication, but you could of course implement a mechanism for passing information back to the host.