I need help understanding this Python program for reading TDS and pH sensors on a Raspberry Pi 4B

Question

I have a Python program for reading both TDS and pH sensors on a Raspberry Pi 4 and sending the data to the Blynk app.

I have a question about the code:

import RPi.GPIO as GPIO
import board
import busio
import time
import sys
import adafruit_ads1x15.ads1115 as ADS
from adafruit_ads1x15.analog_in import AnalogIn
import requests

GPIO.setmode(GPIO.BCM)
GPIO.setup(20, GPIO.OUT)
GPIO.setup(21, GPIO.OUT)
GPIO.output(20, GPIO.HIGH)
GPIO.output(21, GPIO.HIGH)
token="##"

# Setup
i2c = busio.I2C(board.SCL, board.SDA)
ads = ADS.ADS1115(i2c)

def ph_sensor():
    pH = 20
    GPIO.setup(pH, GPIO.OUT)
    GPIO.output(pH, GPIO.LOW)
    channel = AnalogIn(ads, ADS.P0)
    buf = list()
    for i in range(20): # Take 10 samples
        buf.append(channel.voltage)
    buf.sort() # Sort samples and discard highest and lowest
    buf = buf[4:-4]
    avg = (sum(map(float,buf))/12) # Get average value from remaining 6
    ph = round(avg/0.34286,2)
    time.sleep(10)
    GPIO.output(pH, GPIO.HIGH)
    return ph

def ppm():
    TDS = 21
    GPIO.setup(TDS, GPIO.OUT)
    GPIO.output(TDS, GPIO.LOW)
    channel = AnalogIn(ads, ADS.P1)
    buf = list()
    for i in range(20): # Take 10 samples
        buf.append(channel.voltage)#-0.373212)
    buf.sort() # Sort samples and discard highest and lowest
    buf = buf[4:-4]
    avg = (sum(map(float,buf))/6) # Get average value from remaining 6
    ppm = abs(round(((avg*1000)/2.3),2))
    time.sleep(10)
    GPIO.output(TDS, GPIO.HIGH)
    return ppm

def write(token,pin,value):
    api_url = "https://blynk.cloud/external/api/update?token="+token+"&"+pin+"="+value
    response = requests.get(api_url)
    write(token,"v2",str(ppm()))
    time.sleep(5)
    write(token,"v3",str(ph_sensor()))

• In this line of code ph = round(avg/0.34286,2), why do we divide by 0.34286? What does this number even mean?
• In this line of code ppm = abs(round(((avg*1000)/2.3),2)) why do we multiply by 1000 and then divide by 2.3? Can anyone explain?

Answer 1

You have to look at the scaling between the particular sensor that this software was written for and the engineering units that are produced.

For example, I might imagine that the pH sensor produces +2.4V for pH of +7 so by dividing by 0.34286 you get 7.00. Invoking this kind of 'magic number' without comments is a nasty coding style.

The comments are misleading, by the way (eg. 20 samples are taken not 10). And the Python indent formatting (which is part of the syntax) has been destroyed.