To rewrite the provided Arduino code for use on a Raspberry Pi 4 using Python, you'll need to use a Python library for GPIO control and analog input. Raspberry Pi does not natively support analog input, so you will need an external ADC (Analog to Digital Converter) such as the MCP3008 to read the pH sensor. Here's how you can adapt your Arduino …

ph_sensor.py

import time
import spidev
import RPi.GPIO as GPIO

# Set up SPI
spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 1000000

def read_adc(channel):
    """Read a single ADC channel."""
    adc = spi.xfer2([1, (8 + channel) << 4, 0])
    data = ((adc[1] & 3) << 8) + adc[2]
    return data

def setup():
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(13, GPIO.OUT)
    print("Ready")

def loop():
    values = []
    for _ in range(10):
        values.append(read_adc(0))
        time.sleep(0.01)

    values.sort()
    avgValue = sum(values[2:8])
    phValue = (avgValue / 6.0) * (5.0 / 1024)
    phValue *= 3.5

    print(f"    pH: {phValue:.2f} ")
    GPIO.output(13, GPIO.HIGH)
    time.sleep(0.8)
    GPIO.output(13, GPIO.LOW)

if __name__ == "__main__":
    setup()
    while True:
        loop()

Key Changes:

• GPIO and SPI Setup: Uses RPi.GPIO for GPIO and spidev for SPI communication.
• Analog Input: Incorporates the use of an ADC like MCP3008 to read analog values.
• Continuous Loop: The main part of the script that mimics the Arduino's loop() function.

Additional Setup:

Ensure you have the RPi.GPIO and spidev libraries installed on your Raspberry Pi. You can install them using pip if necessary:

pip install RPi.GPIO spidev

Wiring:

• Connect your pH sensor to the MCP3008 ADC.
• Connect the MCP3008 to the SPI pins on your Raspberry Pi (MOSI, MISO, SCK, and CS/CE0).

This setup assumes you're using channel 0 of the MCP3008 for the pH sensor. Adjust the channel in the read_adc function if you use a different channel.