PFR - Aerospace Engineering Sciences Senior Design Projects ...

Project Final Report – CUDBF April 30 th , 2009
ASEN 4028: Aerospace Senior Projects
edge of the signal, it stopped the timer. The timer value reflected how many instruction cycles it
took the microcontroller to read the high time of the incoming signal. Knowing that the
microcontroller operated at a frequency of 48 MHz and executed 4 instructions per clock cycle,
the timer value was converted to a time.
Figure 92: Logic to arming microcontroller
Once the microcontroller was armed it then reads the incoming signals, using the CCP pin as
before, from the aileron, elevator, and rudder. To avoid accidental store release, there is a time
delay of three seconds between arming the microcontroller and the microcontroller reading the
incoming signals. The inputs for these control surfaces are similar to how the switch works. On
the transmitter there are two sticks that produce various PWM signals depending on their
position. For instance, moving the left stick to the far left causes the rudder signal to have a high
time of 1.0 ms or duty cycle of 5% and moving it to the far right gives the rudder a signal with a
high time of 2.0 ms or duty cycle of 10%. Based on the signals, the appropriate payload is
released. The flowchart of this process is shown in Figure 93. Every time the microcontroller is
armed it goes through this sequence once and then returns to the arming routine. Code for the
Microcontroller can be observed in Appendix K.
Figure 93: Flowchart for releasing payloads
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