Not using a pull down resistor can cause that the line keeps high for a longer period than the pulselength (RC effect ?) giving you results you would not expect.
No time to dive into it as one of my own experiments is not working now 
Not using a pull down resistor can cause that the line keeps high for a longer period than the pulselength (RC effect ?) giving you results you would not expect.
No time to dive into it as one of my own experiments is not working now