Excel to work better, faster, and with fewer errors

The program that records the readings

Python reads the Arduino's serial port and writes a CSV file that Excel opens with a double-click. You need Python 3 and the pyserial library.

import csv, time
import serial

# The Arduino sends each reading like this:  24.1,61   (temperature,humidity)
with serial.Serial("COM3", 9600, timeout=2) as arduino, \
     open("readings.csv", "w", newline="") as f:
    out = csv.writer(f)
    out.writerow(["time", "temperature_C", "humidity_%"])
    while True:  # stop with Ctrl+C
        line = arduino.readline().decode().strip()
        if line.count(",") == 1:
            temp, hum = line.split(",")
            out.writerow([time.strftime("%H:%M:%S"), temp, hum])
            f.flush()  # save each reading right away