Change a resistor value with the API, Python

[ElliotG63]

I'm using MultiSim Power Pro Edition, Application Version: 14.3.0 (14.30.49153)

My intent to run multiple simulations under python, I can successfully connect and run the simulator.  I have not been successful in changing a resistor value.  How can I programmatically change a resistor value between runs of DoACSweep()?  

Below I am sharing what I have tried, and a simplified test program.

I have tried using RLCValue(), I can read the resistors value using this call, but I have not been able to set it.

circuit.RLCValue(old_resistor_name, new_value)
# FATAL ERROR: TypeError: RLCValue() takes from 1 to 2 positional arguments but 3 were given

I have also tried to use ReplaceComponent:

circuit.ReplaceComponent(old_resistor_name,  # component name
                         '',  # section name
                         1,  # source database
                         'Basic',  # source group
                         'RESISTOR',  # source family
                         '1k',  # source name
                         '',  # model name
                         )  

# causes a crash with: Process finished with exit code -1073740940 (0xC0000374)

Here is simple example I created to experiment changing a resistor value:

import win32com.client
import os


def replace_resistor(circuit, old_resistor_name, new_value):
    """Replace a resistor with a new resistor of a different value"""
    current_value = circuit.RLCValue(old_resistor_name)  # this works!
    print(f"Current value of {old_resistor_name}: {current_value} ohms")

    # Replace the resistor with a new one of the specified value
    print(f"Replacing resistor...")
    # circuit.ReplaceComponent(old_resistor_name,  # component name
    #                          '',  # section name
    #                          1,  # source database
    #                          'Basic',  # source group
    #                          'RESISTOR',  # source family
    #                          '1k',  # source name
    #                          '',  # model name
    #                          )
    # causes a crash with: Process finished with exit code -1073740940 (0xC0000374)

    circuit.RLCValue(old_resistor_name, new_value)
    # FATAL ERROR: TypeError: RLCValue() takes from 1 to 2 positional arguments but 3 were given

    # Verify the new value
    new_value = circuit.RLCValue(old_resistor_name)
    print(f"New value of {old_resistor_name}: {new_value} ohms")


def main():
    # Create Multisim instance
    multisim = win32com.client.Dispatch("MultisimInterface.MultisimApp")
    multisim.Connect()

    try:
        # Open circuit file
        circuit_path = os.path.abspath("Ibanez_MT10_Mostortion_Schematic.ms14")
        circuit = multisim.OpenFile(circuit_path)
        print("Circuit file opened successfully")

        # Replace the resistor
        replace_resistor(circuit, "GAIN12", 1000.0)

    except Exception as e:
        print(f"Error: {str(e)}")
    finally:
        # Clean up
        multisim.Disconnect()
        print("Disconnected from Multisim")


if __name__ == "__main__":
    main()

Here is the output:

Circuit file opened successfully
Current value of GAIN12: 90000.0 ohms
Replacing resistor...
Error: RLCValue() takes from 1 to 2 positional arguments but 3 were given
Disconnected from Multisim

Thank for any suggestions.  I'm open to taking a different approach. 

[ElliotG63]

I solved my own problem using AI to figure out the low-level COM interface.  If there is a better solution, I would love to know it and get rid of the "magic" solution.  But for now, it works.  This code is a method of a class, self.circuit is the object returned by:

self.circuit = self.multisim.OpenFile(circuit_path)

def set_resistor_value(self, resistor_name, value):
    """Set the value of a resistor in the circuit using direct COM invocation.
    
    Args:
        resistor_name (str): The name of the resistor to set
        value (float): The new resistance value in ohms
    """
    try:
        # Get the _oleobj_ from the circuit object
        oleobj = self.circuit._oleobj_

        # DISPID for RLCValue is 28
        DISPID_RLCVALUE = 28

        # Flags for COM invoke
        DISPATCH_PROPERTYPUT = 0x4

        # print(f"Attempting to set {resistor_name} to {value} ohms...")

        # Make the COM call to set the resistor value
        res = oleobj.InvokeTypes(
            DISPID_RLCVALUE,        # dispid
            0,                      # lcid (locale id)
            DISPATCH_PROPERTYPUT,   # wFlags - PROPERTYPUT for setting a property
            (24, 0),                # retType - VT_VOID
            ((8, 1), (5, 1)),       # argTypes - tuple of tuples: ((type1, flags1), (type2, flags2))
            resistor_name,          # arg1 - resistor name
            value                   # arg2 - new value
        )
        
    except Exception as e:
        print(f"Error setting resistor value: {str(e)}")
        print(f"Last error message: {self.circuit.LastErrorMessage}")
        raise