Temporary low voltage detection using standard deviation for RPI Pico W & CircuitPython

main.py

import analogio
import board
import math
import time

voltage = analogio.AnalogIn(board.VOLTAGE_MONITOR)
voltage_conversion_factor = 3 * 3.3 / 65535

def calculate_mean(data):
    return sum(data) / len(data)

def calculate_std_dev(data, mean):
    variance = sum((x - mean) ** 2 for x in data) / len(data)
    return math.sqrt(variance)

threshold_outlier = -5
threshold_normal = -10
voltage_history = []
voltage_low = False

while len(voltage_history) < 1000:
    voltage_history.append(voltage.value * voltage_conversion_factor)

while True:
    battery_voltage = voltage.value * voltage_conversion_factor
    voltage_history_copy = voltage_history[:]
    voltage_history_copy.append(battery_voltage)

    voltage_average = calculate_mean(voltage_history_copy)
    voltage_std_dev = calculate_std_dev(voltage_history_copy, voltage_average)
    z_scores = [(x - voltage_average) / voltage_std_dev for x in voltage_history_copy]

    if any(z_score < threshold_outlier for z_score in z_scores):
        if not voltage_low:
            voltage_low = True
            print("Low voltage outlier detected!")
    else:
        voltage_history = voltage_history_copy
        if voltage_low:
            voltage_low = False
            print("Voltage back to normal.")
        
    if len(voltage_history) > 1000:
        voltage_history.pop(0)

    print(f"Voltage: {battery_voltage:0.02f} | Average: {voltage_average:0.02f}")
    time.sleep(0.5)