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Network RC Car

Learn how to utilize a microprocessor to modify camera output signals for precise control of an RC car. Explore pulse width modulation, clock frequency adjustments, setting duty cycles, and utilizing capture timers for enhanced control.

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Network RC Car

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Presentation Transcript

  1. Network RC Car Seth Schwiethale James Crosetto James Ellison

  2. Car’s Input • square pulse of 1.0-2.0 ms, repeats every 20 ms • It is the same for both steering and acceleration • width of the pulse determines the direction/speed w/ 1.5 ms as the nominal center • the amplitude of the pulse is from the reference level of the Vcc (5v)

  3. Camera’s Output • 1 “alarm” output • max activation is 100 times/sec (increments of 10 ms)

  4. The Problem • Camera’s output can’t produce a 20ms PWM signal that is highbetween 1-2ms • Car cannot be driven by Camera directly • need something that modifies the output signal of the camera so it can be used by the car

  5. The Solution • Using a microprocessor (MC9S12DP256) • has a clock signal rate of 24MHz • has registers for a Pulse Width Modulator and an Enhanced Capture Timer • Signal from the camera can be varied between 10-110ms for speed and 120-220ms for steering

  6. Pulse Width Modulation camera’s output microprocessor car’s input

  7. Pulse Width Modulator • used to create correct output signal • uses CPU clock signal to generate signal lengths • current signal is 24MHz and we need a 50Hz (20ms) signal (Factor of 480000!)

  8. Determining the Output Signal • Initializing the Pulse Width Modulator

  9. Modifying the Clock Frequency • The pulse width modulator uses registers to decrease the frequency of the clock signal before it is used as an output signal • Two output signals can be generated from the clock signal Allows for finer control of signal

  10. Setting the Period • The periods of both SA and SB need to be 20ms

  11. Setting the Duty Cycle • The duty cycle (the part of the PWM signal that is high) needs to be 1-2ms in length • Initialized to 1.5 ms Notice the difference!

  12. Pulse Width Modulation Code

  13. Enhance Capture Timer • Used to trigger interrupts • Set up to trigger an interrupt every time a signal goes high or low on an input port (TCTL4 and TIE)

  14. Counting • Timer Register (TCNT) is incremented every clock cycle (24MHz clock = 24 million times per second) • Clock slowed to 187.5 KHz • TCNT is 16-bit register (0-65535) • Overflows about every 1/3 second (65535/187500) • Never overflows more than once per input signal from camera

  15. Interrupt

  16. Conclusion

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