import machine
import time

gas_sensor = machine.ADC(26)
buzzer = machine.Pin(15, machine.Pin.OUT)

stepper_1a_plus = machine.Pin(10, machine.Pin.OUT)
stepper_1a_minus = machine.Pin(11, machine.Pin.OUT)
stepper_1b_plus = machine.Pin(12, machine.Pin.OUT)
stepper_1b_minus = machine.Pin(13, machine.Pin.OUT)

led = machine.Pin(25, machine.Pin.OUT)

GAS_THRESHOLD = 20000
SENSOR_READING_INTERVAL = 0.5
STEPPER_STEP_DELAY = 0.002

bipolar_sequence = [
    [1, 0, 1, 0],  # Step 1
    [0, 1, 1, 0],  # Step 2
    [0, 1, 0, 1],  # Step 3
    [1, 0, 0, 1]   # Step 4
]

fan_running = False

buzzer_pwm = machine.PWM(buzzer)
buzzer_pwm.freq(1000)  
buzzer_pwm.duty_u16(0)  

def set_alarm(state):
    """Controls the buzzer."""
    if state:
        buzzer_pwm.duty_u16(32768) 
    else:
        buzzer_pwm.duty_u16(0)  

def control_fan(enable):
    """Starts or stops the stepper motor (fan)."""
    global fan_running
    
    if enable and not fan_running:
        fan_running = True
    elif not enable and fan_running:
        
        stepper_1a_plus.value(0)
        stepper_1a_minus.value(0)
        stepper_1b_plus.value(0)
        stepper_1b_minus.value(0)
        fan_running = False

def step_motor():
    """Runs the stepper motor continuously when fan is ON."""
    for _ in range(200):  
        for step in bipolar_sequence:
            stepper_1a_plus.value(step[0])
            stepper_1a_minus.value(step[1])
            stepper_1b_plus.value(step[2])
            stepper_1b_minus.value(step[3])
            time.sleep(STEPPER_STEP_DELAY)

def read_gas_level():
    """Reads the MQ-2 gas sensor."""
    return gas_sensor.read_u16()

def is_gas_level_critical(gas_level):
    """Checks if gas level exceeds the threshold."""
    return gas_level > GAS_THRESHOLD

print("Gas Detection System Starting...")
print("Warming up MQ2 sensor...")
time.sleep(5)
print("System ready!")

try:
    while True:
        gas_level = read_gas_level()
        print("Gas Level:", gas_level)
        
        if is_gas_level_critical(gas_level):
            led.value(1)  
            set_alarm(1)  
            control_fan(True)  
            
            if fan_running:
                step_motor()
        else:
            led.value(0)  
            set_alarm(0)  
            control_fan(False)  
        
        time.sleep(SENSOR_READING_INTERVAL)
        
except KeyboardInterrupt:
    set_alarm(0)
    control_fan(False)
    led.value(0)
    print("System stopped.")