Week11. Output Devices#

  • Author : jun kawahara (Fablab Kamakura)
  • Date created : 03/01/2019
  • modified: 04/18/2020 (Kai Naito)
  • modified: 04/20/2021 (Rico Kanthatham)
  • modified: 15/02/2022 (Jun Kawahara)
    • Updated for 2022 evaluation standards

This is the fourth week of five electronics-related assignments.

  • Electronics Production: You will learn how to make circuits
  • Electronics Design: You will learn how to design them
  • Embedded Programming: You will learn how to program them
  • Output Devices: You will learn how to bring output out of them
  • Input Devices: You will learn how to bring input into them


from Assessment - Onput Devices

  • Group assignment:

    • Measure the power consumption of an output device
    • Document your work to the group work page and reflect on your individual page what you learned
  • Individual assignment:

    • Add an output device to a microcontroller board you’ve designed and program it to do something
  • Learning outcomes

    • Demonstrate workflows used in controlling an output device(s) with MCU board you have designed
    • Have you answered these questions?
    • Linked to the group assignment page
    • Documented how you determined power consumption of an output device with your group
    • Documented what you learned from interfacing output device(s) to microcontroller and controlling the device(s)
    • Described your design and fabrication process or linked to previous examples.
    • Explained the programming process/es you used.
    • Outlined problems and how you fixed them
    • Included original design files and code
    • Included a ‘hero shot/video’ of your board
  • FAQ

    • What is the point of the group excercise?
      Answer: Different output devices need different amounts of energy to function. You need to be able to choose suitable power source for your projects.
    • Is it ok to use the LED in the hello board as an output device for this assignment?
      Answer: No, you need to do more.

Class review#

Random Notes from Neil’s Lecture

Electrical safety#

  • 9V under the skin can kill you
  • Capacitors store charge for a long time and be dangerous…be careful not to touch
  • Coils have snapback voltage risk…hurts you, fry electronics…use protective diodes
  • Higher voltages and currents are dangerous…take good care like CNC machine
  • Output device list arranged from low to high current components
  • Use power supply to power system…not disposable batteries
  • 4-ways to measure power consumption
    1) regulated supply…device measures for your
    2) 1 ohm resistor at ground return…voltage drop/resistance
    3)Hall sensor …measure mag field around it

Different Power Supplies#

  • Switching (efficient, cheap, noisy)
  • Linear (inefficient, expensive, clean)
  • Regulated (AC>DC, constant output, controllable output voltage)
  • Battery (LiPo, special charger, safety concerns, fireproof storage)

Current Measurement#

  • supply regulation
  • sense resistor
  • magnetic field
  • inductance

output devices#

There are many output options…lights, sounds, motion, etc…that can be controlled by the MCU. Each output device has unique…power, signal, circuitry, communication requirements

  • RGB LEDs

    • requires current limiting resistor…different size for different colors
    • PWM to control brightness
  • LEDs

    • A diode (polarized…orientation matters!)…pair with a current limiting resistor
    • Neil’s super bright LEDs will require eye protection!!!
  • LED Array

    • Charlieplexing…tri-state logic by microcontrollers to gain efficiency over traditional multiplexing.
      • n MCU pins can drive…n-squared minus n LEDs
  • Displays

    • LCD…arduino LiquidCrystal library. PCF8574 is 2-line liquid crystal display, i2C connection (2 pins only!!), LiquidCrystal for i2c library.
      • 1602: 16 characters in 2-line
      • 4004: 40 characters in 4-line
    • OLED…Adafruit_SSD1306 library for SSD1306 drivers…i2C or SPI to communicate, 2 to 5 pins required
    • TFT…library
  • Solenoid

    • Magnetic field control with coiled copper wire…to move a metal shaft (quickly over a short distance)
    • Push-Pull type or Pull type
    • turning on an electromagnetic field moves the shaft (switch actuation)
    • recommend using a MOSFET (rated for the solenoid’s current draw, controlled by microcontroller) as actuating switch for the solenoid
    • reversing the polarity of the coil changes the direction the central shaft moves
    • draws a lot of current relative to other output devices…~2A
    • an inductive load device…use a diode to control ‘flyback’ voltage
    • should not be used continuously…needs cooling…25% duty cycle, typical (25% time on, 75% time off)
    • Control a Solenoid with an Arduino
  • Sound

    • MCU sends PWM signals to the speaker to generate sound
    • Transistor for amplification
    • Speaker’s resistance value should be noted…Arduino can supply 5V at max 40mA >> 5/0.4 = 120 ohms
    • recommended capacitor put in series (high pass filter) with speaker to remove DC component of PWM signal…allow speaker to move in and out with positive and negative voltages…1000uF for low audio frequencies of 4 or 8 ohms…lower for higher audio frequencies
    • Electronic sounds via Arduino sound libraries
    • use PCM to playback MP3 audio files from a PC by uploading it to the Arduino (file size must be reduced to about 15kb…reduce sampling bit-rate and project rate Hz)
    • How to play Audio with Arduino
  • Peltier

    • Temperature control by the Peltier Effect
    • Peltier Effect…current flow between two junctions (of different conductive material…copper/bismuth) causes heating (copper>bismuth) or cooling (bismuth>copper)
    • Modern Peltier devices built using semiconductors…alternate P and N type semiconductors arranged in a matrix…sandwiched between conductive sheets (positive on top, negative on bottom)…and outside layers of ceramic thermal conductive plates
    • TEC1-12706 Device
      • TE = Thermoelectric
      • C = Standard Size (S = small)
      • 1 = Layers (most have only 1)
      • 127 = number of P-N semiconductor junctions
      • 06 = max current rating in amperes
    • One side of device gets cold…the other gets cold. Reversing the polarity changes which side gets hot or cold
    • Heat sink recommended on the hot side
    • Peltier device can be use to generate electricity!! (…by heating or cooling one side)
    • Peltier Effect Cooling
  • Stepper Motor

    • Precise angular position of motor rotor without feedback loop…an accurate open-loop system
    • Unipolar or Bipolar stepper motor types
    • NEMA = National Electrical Manufacturers Association
      • 17 or 23 (or other) = distance between mounting holes in inches * 10
    • Step size (step angle)…measured in degrees
    • Steps = 360 degree / step angle
    • Rotor motion by energizing different coil pairs
    • Rated Voltage and Current = the maximum voltage and current draw for the stepper motor to operate at max efficiency and long life; higher voltages means more current draw but excessive heat generated.
    • Stepper motor coils are connected in groups called ‘Phases’
    • phase excitation
      • 1 phase(wave mode): full step, not for practical use
      • 2 phase: full step, commonly used
      • 1-2 phase: half step, a combination of 1 phase + 2 phase.
      • Microstepping = dividing the step angle into smaller steps (up to 256 times)…via PWM voltages to control current to coils…gradually decreasing from one coil pair to the next coil pair; microstepping generates smoother motion and more consistent torque…but lower torque than full-step
    • Stepper Motor Driver = current regulator (and microstep resolution adjuster) using high frequency pulses to limit the average current
      • energizes the phases in a timely sequence to make the motor turn accurately
      • usually requires a heat sink on the chip
      • should match current rating of driver to motor
      • don’t disconnect stepper motor driver wire from a driver while powered or cause permanent damage
      • Interface
        • Step/Direction
        • Phase/Enable
        • In/In (PWM)
        • etc.
    • Dual H-Bridge driver required for bipolar motor
    • Unipolar driver for unipolar motors…simple circuits comprised of transistors…switched on/off in sequence to energize the phases and step the motor
    • Holding Torque = resistance to rotor rotation when the motor is stationary; an advantage of stepper vs servo motors; limited by the max current the motor can handle
    • Stepper motors draw power even when not moving
    • references

Group Assignment#

Individual Assignment#

output devices in lab inventory#