Python • Re: Using a 4-20 mA Transmitter with a Raspberry Pi

Code:

import timefrom smbus2 import SMBusDAC_ADDRESS = 0x60class CurrentLoopTransmitter:    """    NCD 1-Channel 4-20mA Current Loop Transmitter    MCP4725 DAC + XTR115    """    SET_VOLTAGE = 0x40   # Write DAC register (normal mode)    LOWER_LIMIT = 670    UPPER_LIMIT = 3460    MAX_LOOP_VOLTAGE = 36    def __init__(self, bus, address=DAC_ADDRESS, resistor=None):        self.bus = bus        self.address = address        self.resistor = resistor        if resistor is not None:            self.max_voltage = resistor * 20e-3            self.min_voltage = resistor * 4e-3    def set_current(self, current_mA: float):        if not 4 <= current_mA <= 20:            raise ValueError("Current must be between 4 and 20 mA")        raw_value = round(            (current_mA - 4) / 16 * (self.UPPER_LIMIT - self.LOWER_LIMIT) + self.LOWER_LIMIT        )        msb = (raw_value >> 4) & 0xFF        lsb = (raw_value & 0x0F) << 4        try:            self.bus.write_i2c_block_data(self.address, self.SET_VOLTAGE, [msb, lsb])        except OSError as e:            print(f"I²C Error while writing DAC value: {e}")            raise    def set_voltage(self, voltage: float):        if self.resistor is None:            raise RuntimeError("Resistor must be specified for voltage mode")        if voltage > self.MAX_LOOP_VOLTAGE:            raise ValueError(f"Max loop voltage is {self.MAX_LOOP_VOLTAGE} V")        if not self.min_voltage <= voltage <= self.max_voltage:            raise ValueError(                f"Voltage {voltage:.2f} V out of range ({self.min_voltage:.2f}–{self.max_voltage:.2f} V)"            )        current_mA = voltage / self.resistor * 1000        print(f"Voltage: {voltage:5.2f} V | Current: {current_mA:5.2f} mA")        self.set_current(current_mA)def sweep_values(start, stop, steps, duration):    """    Sweep linearly between start and stop and back.    Total duration ≈ duration seconds.    """    delta = (stop - start) / steps    delay = duration / (steps * 2)    for step in range(steps + 1):        yield start + delta * step        time.sleep(delay)    for step in reversed(range(steps)):        yield start + delta * step        time.sleep(delay)                        cl1 = CurrentLoopTransmitter(SMBus(1), resistor=500)cl1.set_voltage(10)cl1.set_voltage(9.4)cl1.set_voltage(2)cl1.set_current(20)try:    cl1.set_voltage(1)except ValueError:    print("CurrentLoopTransmitter has thrown ValueError.")    print(f"The lower limit is currently {cl1.min_voltage}V with a {cl1.resistor}Ω  Resistor.")    print(f"The upper limit is currently {cl1.max_voltage}V.")for voltage in sweep_values(2, 10, 10, 1):    print(f"Setting voltage to {voltage:5.2f}V")    cl1.set_voltage(voltage)