This doesn't implement start or stop bits, or any parity or flow control. It also doesn't implement default high, but default low as a replacement.
This is to test how varying line capacitance, and varying line termination (or pullup), makes the overall serialized system respond, being more or less prone to error.
To test, adjust the capacitance of the capacitor, and the resistance of the first resistor, and the resistance of the second resistor. Then inject noise, and see if that has an effect on what the 7 segment display shows on the right hand side relative to the left hand side.
