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Hybrid I/O – Pulses

Hybrid I/O – Pulses. Digital or Analog?. +5 V. 0 V. It depends on how data is encoded . Analog Signals that Look Awfully Digital…. Pulse Generation Pulse-Width Modulation (PWM) Pulse-Width Measurement (PWM) Event counting Period Measurement Input capture Output compare

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Hybrid I/O – Pulses

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  1. Hybrid I/O – Pulses

  2. Digital or Analog? +5 V 0 V It depends on how data is encoded.

  3. Analog Signals that Look Awfully Digital… • Pulse Generation • Pulse-Width Modulation (PWM) • Pulse-Width Measurement (PWM) • Event counting • Period Measurement • Input capture • Output compare For a microcontroller – all involve creative use of clocks and counters

  4. Applications of These Signals Applications: • Pulse Generation (sensors, motors, general control) • Pulse-Width Modulation (PWM) (DC Motors) • Pulse-Width Measurement (PWM) (sensors) • Event counting • Period Measurement (frequency measurement/modulation) • Input capture (pattern recognition) • Output compare (timed patterns)

  5. Magnetic Fields Direction of Field: North  South

  6. Right Hand Rule Electric Currents  Magnetism!

  7. Right Hand Rule Electric Currents  Magnetism!

  8. Electromagnet North/South Pole?

  9. Stepper Motor

  10. Stepper Motor

  11. Stepper Manipulation • Controlling a stepper involves turning these electromagnets on and off • This must be done in order to create rotation. • i.e. can’t go from top one high to bottom one high • Microcontroller will want to set up its outputs to go through these steps in order by generating pulses on multiple pins • Number of steps (resolution) can actually be doubled with creative pulsing • i.e. top and right on give you a position going “NE”

  12. Right Hand Rule # 2 Electric Currents & Magnetism  Force Force Current Magnetic Field

  13. Force in a Conductor

  14. Force in a Conductor

  15. Diagram of a Simple DC Motor

  16. Commutator

  17. DC Motor Velocity • The velocity of the motor is (roughly) proportional to the force exerted • The power of the force acting on the motor is directly proportional to the magnetic field that is causing the force • The magnetic field intensity is directly proportional to the current that creates it (from running through the wires) • The current is directly proportional to the Voltage across the lines (V = IR) Therefore: The speed of the motor is directly proportional to the Voltage How do I output a voltage?!?

  18. Pulse Width Modulation (PWM) Effective Voltage = Duty Cycle x Supply Voltage

  19. Single Pulse Applications • Sensors: • Ultrasonic range-finders require a pulse to start ranging, and report results based on a pulse length • Servo Motors: • Pulse width describes position

  20. Generating Pulsed I/O on the MPC555 • “Obvious” answer is to use straight GPIO (digital I/O), like the port we used in the QADC, then use the PIT to do timings • While possible, to do a continuous pulse we have to interrupt the processor every ½ period! • Timing is also slightly less accurate (going to an ISR takes time) • The MPC555 has a “MIOS” unit (Modular Input/Output System) • Combines counters and clocks to generate a wide range of pulse widths and periods. • Does so without the need for interrupts

  21. MDASM Modes • Disable mode • Pulse width measurement • Period measurement • Input capture mode • Single pulse generation • Continuous pulse generation

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