def string_split(input_string):
    """Split a string based on the presence of commas

    Each line of the file is read in as a single string, so it is necessary
    to separate this string into two categories: time and voltage. Given that
    the file is comma separated, this function is used to split each string
    into the two categories mentioned above. The input_string will have the
    following format:
    input_string = "0.#####,1.#####"
    Once the string is split, the function returns a list, where the
    first element in the list is the time, and the second element
    in the list is the voltage. This output list has the following format:
    output = ["0.#####". "1.#####"]

    Parameters
    ----------
    input_string : string
        Contains the time and voltage combined as a single string

    Returns
    -------
    list
        List containing two strings
    """
    output = input_string.split(",")
    return output