from machine import ADC, I2C, Pin
from machine_i2c_lcd import I2cLcd
import time

#lcd setup 
i2c = I2C(0, sda=Pin(4), scl=Pin(5), freq=400000)
lcd = I2cLcd(i2c, 0x27, 2, 16)
adc = ADC(26)

# PULL_DOWN: pin reads 0 normally, goes to 1 when button is pressed
btn_left  = Pin(10, Pin.IN, Pin.PULL_DOWN)
btn_right = Pin(11, Pin.IN, Pin.PULL_DOWN)

# Modes for menu 
modes = ["Voltage", "Current", "Resistance", "Capacitance"]
current_mode = 0

# screen intro
lcd.clear()
lcd.putstr("  Multimeter  ")
time.sleep(2)

# main loop
while True:

    # left button - reads 1 when pressed
    if btn_left.value() == 1:
        if current_mode > 0:
            current_mode = current_mode - 1
        time.sleep(0.3)  # debounce

    # right button - reads 1 when pressed
    if btn_right.value() == 1:
        if current_mode < len(modes) - 1:
            current_mode = current_mode + 1
        time.sleep(0.3)  # debounce

    # Read the potentiometer
    raw   = adc.read_u16()        # gives a number from 0 to 65535
    volts = raw * 3.3 / 65535     # convert to volts (0.0 to 3.3)

    # Work out what to display based on the selected mode
    if modes[current_mode] == "Voltage":
        reading = str(round(volts, 2)) + " V"

    elif modes[current_mode] == "Current":
        # Simulated: using 100 ohm, formula used is I = V / R
        amps = volts / 100
        reading = str(round(amps * 1000, 2)) + " mA"

    elif modes[current_mode] == "Resistance":
        # Voltage divider with known 1k resistor: R = R_known * V / (Vcc - V)
        if volts >= 3.28:
            reading = "Overload"
        else:
            ohms = 1000 * volts / (3.3 - volts)
            reading = str(round(ohms, 1)) + " Ohm"

    elif modes[current_mode] == "Capacitance":
        # RC time constant formula: C = t / R
        # The pot voltage (0 to 3.3V) maps to a simulated charge time (0 to 0.033 seconds)
        # Fixed known resistor R = 10,000 ohms (10k)
        # So C = t / R gives a range of 0 to 3.3 uF
        R = 10000
        t = (volts / 3.3) * 0.033   # simulated time in seconds (0 to 33ms)
        C = t / R                    # capacitance in Farads
        C_uf = C * 1000000           # convert to microfarads
        reading = str(round(C_uf, 2)) + " uF"

    #below is what is outputted on lcd
    lcd.clear()
    lcd.putstr(modes[current_mode])
    lcd.move_to(0, 1)
    lcd.putstr(reading)

    time.sleep(0.3)