PFR - Aerospace Engineering Sciences Senior Design Projects ...

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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects The board features a PIC18F2553 microcontroller, which has one compare, capture, and PWM (CCP) pin. The CCP pin is used to read in the PWM signal from the receiver. Due to the fact that the board only had one CCP pin, only one signal could be read from the transmitter, thus the board was used for proof-of concept. In order to read all of the required incoming signals, a multiplexer chip was implemented. On the board there are digital input/output pins that can be set high or low in software and the state of these pins can be read into the multiplexer chip with the corresponding signal from the transmitter. In other words, each signal (rudder, elevator, aileron, and switch) will be one of the inputs into the multiplexer and the digital I/O pins will be the other input. The output of the multiplexing chip is then connected to the CCP pin and depending what the PWM signal is the desired servo will be controlled. Table 22 illustrates how the output of the multiplexer is determined and Figure 83 illustrates how everything is wired. Table 22: Determination of output from multiplexer A (I/O Pin) B (I/O Pin) Switch Aileron Elevator Rudder Output L L L X X X L L L H X X X H L H X L X X L L H X H X X H H L X X L X L H L X X H X H H H X X X L L H H X X X H H Figure 83: Wiring Diagram The power distribution board on the diagram illustrates that the PWM signal outputted by the microcontroller cannot power the servos; a 5 V battery must be used to provide power to the 106
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects servos. Also it is important that the electrical devices are properly grounded, to prevent the devices from blowing up. With the assistance from one of our graduate advisors, Josh Fromm, the team was able to design a fully functioning circuit board. The completed circuit board is shown in Figure 84. The circuit board layout can be observed in Figure 85. Figure 84: Completed Circuit Board Figure 85: Circuit Board Schematic 107
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University of Colorado Design/Build
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PFR - Aerospace Engineering Sciences Senior Design Projects ...

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