BLDC Motor Speed control with Hobbyking ESC

I am using an STM32F3 Discovery board to generate a control signal for the Hobbyking ESC. I manipulate the control signal using a Python script that communicates with my STM board via a COM port on Catrinas computer. The signal frequency is set at 66HZ. The Python script uses a slider from the TKinter library to let me quickly select a value between 4 and 16 which represent a duty cycle percentage. The low end 4% gives me a pulse width of about 1ms at 66HZ while the 16% duty cycle gives me an output pulse of about 2ms.These are the bounds within which the pulse must be varied to achieve the minimum and maximum throttle signal for the ESC.
The bigger board is the flight controller and has a switching 5v regulator. The smaller board has a DB9 connector to interface with my USB/serial converter as well as a 232/UART level shifter.