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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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digital or analog
Digital or Analog?

+5 V

0 V

It depends on how data is encoded.

analog signals that look awfully digital
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

applications of these signals
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)
magnetic fields
Magnetic Fields

Direction of Field: North  South

right hand rule
Right Hand Rule

Electric Currents  Magnetism!

right hand rule1
Right Hand Rule

Electric Currents  Magnetism!

electromagnet
Electromagnet

North/South Pole?

stepper manipulation
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”
right hand rule 2
Right Hand Rule # 2

Electric Currents & Magnetism  Force

Force

Current

Magnetic Field

dc motor velocity
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?!?

slide18

Pulse Width Modulation (PWM)

Effective Voltage = Duty Cycle x Supply Voltage

single pulse applications
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
generating pulsed i o on the mpc555
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
mdasm modes
MDASM Modes
  • Disable mode
  • Pulse width measurement
  • Period measurement
  • Input capture mode
  • Single pulse generation
  • Continuous pulse generation