import time
from machine import SoftI2C, Pin, ADC
from machine_i2c_lcd import I2cLcd

time.sleep(0.1)

# ---------------- LCD ----------------
i2c = SoftI2C(scl=Pin(26), sda=Pin(27), freq=400000)
lcd = I2cLcd(i2c, 0x27, 4, 20)

# ---------------- ADC ----------------
adc = ADC(28)

VREF = 3.3
ADC_MAX = 65535

# ---------------- SWITCHES ----------------
s1 = Pin(16, Pin.IN, Pin.PULL_UP)
s2 = Pin(17, Pin.IN, Pin.PULL_UP)
s3 = Pin(18, Pin.IN, Pin.PULL_UP)
s4 = Pin(19, Pin.IN, Pin.PULL_UP)

# ---------------- RANGE SELECTION ----------------
def get_r_known():
    if not s1.value():
        return "100 Ohms"        # 0–100Ω range
    elif not s2.value():
        return "1k Ohms"       # 100Ω–1kΩ
    elif not s3.value():
        return "10k Ohms"      # 1kΩ–10kΩ
    elif not s4.value():
        return "100k Ohms"     # 10kΩ–100kΩ
    else:
        return None

# ---------------- ADC VOLTAGE ----------------
def read_voltage():
    raw = adc.read_u16()
    return (raw / ADC_MAX) * VREF

# ---------------- RESISTANCE CALC ----------------
def measure_resistance():
    r_known = get_r_known()
    if r_known is None:
        return None, None

    v_out = read_voltage()

    # invalid region checks (avoid divide errors / saturation)
    if v_out <= 0.001 or v_out >= (VREF - 0.001):
        return r_known, None

    r_unknown = r_known * (v_out / (VREF - v_out))
    return r_known, r_unknown

# ---------------- DISPLAY ----------------
def display(r_known, r_unknown):
    lcd.clear()

    # Line 1: Resistance
    lcd.move_to(0, 0)
    if r_unknown is None:
        lcd.putstr("Resistance:")
    else:
        lcd.putstr("Resistance: " + str(int(r_unknown)))

    # Line 2: Range
    lcd.move_to(0, 1)
    if r_known is None:
        lcd.putstr("Range: NONE")
    else:
        lcd.putstr("Range: " + r_known)

# ---------------- MAIN LOOP ----------------
while True:
    r_known, r_unknown = measure_resistance()
    display(r_known, r_unknown)
    time.sleep(3)