import time, math, machine

# Constants
SEGMENT_START_PIN = 0                # Starting GPIO pin for segment control
ANALOG_IN = 26                       # ADC pin connected to sensor
BUTTON_IN = 16                       # GPIO pin for push button input
DIGITs_COUNTs = 4                    # Number of digits in the 7-segment display
SAMPLE_AVERAGE = 10                  # Number of ADC samples to average
DECIMAL_PLACES = 3                   # Decimal precision for voltage display
ADC_HIGHEST_VALUE = 65535            # Max value from 16-bit ADC reading
pushBUTTON_DEBOUNCE = 50             # Debounce time in milliseconds

# 7-segment encoding for hexadecimal digits 0-F + blank (last entry)
SEGMENT_CODES = [
    0x40, 0x79, 0x24, 0x30, 0x19, 0x12, 
    0x02, 0x78, 0x00, 0x10, 0x08, 0x03,
    0x46, 0x21, 0x06, 0x0E, 0x7F
]

# Global variables
current_display_NO = 0                  # Value currently displayed
previous_V_reading = -1                 # Previous voltage to detect changes
last_button_press = 0                   # Timestamp of last button press
active_digit_place = DIGITs_COUNTs - 1  # Current digit being refreshed
control_pins = []                       # Pins for segments (a-g, dp)
select_pins = []                        # Pins to activate specific digit positions
V_sensor = None                         # ADC object
push_button = None                      # Button input pin object
refresh_timer = None                    # Timer for display multiplexing

# Measures voltage from ADC and triggers display update if it changes
def measure_voltage(adc_pin):
    global current_display_NO, previous_V_reading
    try:
        raw_readings = []
        for _ in range(SAMPLE_AVERAGE):
            raw_readings.append(adc_pin.read_u16())  # Read ADC value
            time.sleep_us(100)
        raw_avg = sum(raw_readings) // len(raw_readings)
        measured_voltage = round((raw_avg / ADC_HIGHEST_VALUE) * 3.3, DECIMAL_PLACES)
        if measured_voltage != previous_V_reading:
            previous_V_reading = measured_voltage
            display_integer = min(int(measured_voltage * 10**DECIMAL_PLACES), 10**DIGITs_COUNTs - 1)
            if current_display_NO != display_integer:
                current_display_NO = display_integer
                reset_display()
            return measured_voltage
    except Exception as e:
        print(f"Error reading voltage: {e}")
        return None

# Updates one digit of the 7-segment display in a multiplexed fashion
def update_display_segments(timer):
    global active_digit_place
    digit_value = int(abs(current_display_NO) // 10**active_digit_place) % 10
    show_decimal = active_digit_place == DECIMAL_PLACES and DECIMAL_PLACES != 0
    illuminate_digit(digit_value, active_digit_place, show_decimal)
    active_digit_place = (active_digit_place - 1) % DIGITs_COUNTs

# Lights up a single digit with given value and optional decimal point
def illuminate_digit(value, position, decimal_point=False):
    if 0 <= value < len(SEGMENT_CODES):
        for pin in select_pins: pin.value(0)  # Turn off all digits
        segment_mask = SEGMENT_CODES[value]   # Get segment pattern
        for segment in range(7):
            control_pins[segment].value((segment_mask >> segment) & 1)  # Set segments a-g
        control_pins[7].value(not decimal_point)  # Decimal point (dp) logic
        if 0 <= position < DIGITs_COUNTs: select_pins[position].value(1)  # Enable one digit

# Resets and restarts display refresh timer
def reset_display():
    global active_digit_place
    refresh_timer.deinit()                   # Stop current timer
    active_digit_place = DIGITs_COUNTs - 1   # Start from rightmost digit
    illuminate_digit(16, -1)                 # Clear display (16 is blank code)
    time.sleep(0.1)
    refresh_timer.init(period=4, mode=machine.Timer.PERIODIC, callback=update_display_segments)

# Initializes pins and timer
def initialize_hardware():
    global control_pins, select_pins, V_sensor, push_button, refresh_timer
    V_sensor = machine.ADC(ANALOG_IN)  # Set up ADC pin
    push_button = machine.Pin(BUTTON_IN, machine.Pin.IN, machine.Pin.PULL_UP)  # Button with pull-up
    select_pins = [machine.Pin(pin_num, machine.Pin.OUT) for pin_num in range(SEGMENT_START_PIN + 8, SEGMENT_START_PIN + 8 + DIGITs_COUNTs)]  # Digit selectors
    control_pins = [machine.Pin(pin_num, machine.Pin.OUT) for pin_num in range(SEGMENT_START_PIN, SEGMENT_START_PIN + 8)]  # Segment controls
    refresh_timer = machine.Timer()  # Timer object
    reset_display()  # Start display refresh

# Main loop
if __name__ == '__main__':
    print("Starting digital voltmeter...")
    time.sleep(2.5)
    print("set the (LDR -or- NTC -or- slide potentiometer) before running the program..")
    time.sleep(2.5)
    print("press the button to see the voltage measurement on the multi 7-segment.... ")
    initialize_hardware()
    while True:
        # Check button press with debounce
        if push_button.value() == 0 and time.ticks_ms() - last_button_press > pushBUTTON_DEBOUNCE:
            last_button_press = time.ticks_ms()
            voltage = measure_voltage(V_sensor)  # Read and display voltage
            if voltage is not None: print(f'Current Voltage: {voltage} V')
        time.sleep(0.1)