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Electronic Devices for the Mechanical Experimenter*

Electronic Devices for the Mechanical Experimenter*. Nathan Delson. *Title inspired by book, Mechanical Devices for the Electronics Experimenter. MEs are Responsible for More and More EE Design. Electronics and Microprocessors are pervasive in mechanical devices

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Electronic Devices for the Mechanical Experimenter*

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  1. Electronic Devices for the Mechanical Experimenter* Nathan Delson *Title inspired by book, Mechanical Devices for the Electronics Experimenter

  2. MEs are Responsible for More and More EE Design • Electronics and Microprocessors are pervasive in mechanical devices • Electrical Engineering Education is very focused on topics such chip design and wireless communication • Leaving gaps in sensor integration and motor control • Even if an EE is doing the electronics design, MEs need familiarity with electronics to communicate effectively.

  3. Good Electronic Design vs. Bad Electronic Design Bad EE Design • Copy circuits without voltage or current calculations, and no use of spec sheets • Circuits seem to work or not by “magic” Good EE Design • Use of specification (spec) sheets • Clear circuit diagrams, with voltage AND current calculations • Step by step implementation, with verification of each step with a voltmeter or oscilloscope • Good wiring habits: consistent colors, strain relief, and others described on the “Hands-on Guidelines for Good Circuit Implementation”

  4. Like with ME Components, EE Components have input, output, and power specs Example of an ME Component Specs: Transmissions • Input speed and torque • Output speed and torque • Power rating • Other specs: Friction, backlash, size, weight, … Specs for EE Components Include • Input voltage and current • Output voltage and current • Overall power dissipation and power handling capabilities • Remember: P = VI

  5. Categories of EE Components

  6. Categories of EE Components

  7. Light Emitting Diode (LED) Use a spec sheet so you do not burn it out! From Spec sheet: • Continuous forward current = 40mA • Forward Voltage = 1.7 V What resistance would you use for maximum LED brightness? Many components can be overdriven for a short period of time • Peak forward current (1/10 Duty Cycle, 0.1ms Pulse Width) = 200 mA

  8. Microprocessor: The 16F877A PIC on the X2 Board 16F877A PIC is a digital microprocessor where 0V corresponds to low (logical 0), and 5V corresponds to high (logical 1) Key Features • 33 total I/O pins • 8 analog inputs (10 bit) • 2 hardware PWM output channels • Total memory: 14336 bytes Specs for digital input • reads low for v<0.8 and high for V> 2 Specs for Digital Output with a 5V supply • maintains low (V=0 to 0.6) by sinking up to 25 mA per pin • maintains high (V=5 to 4.7) by sourcing up to 25 mA per pin • Total of all pins cannot source or sink more than 200 mA.

  9. Input Switch – INCORRECT Method

  10. Input Switch Correct Method: Avoids Floating Input Brain teaser: Can you connect switch so signal to PIC is low when switch is closed, and high when switch is open.

  11. Potentiometer How would you hook up a potentiometer so it could generate available input voltage to be read by a PIC?

  12. DC Permanent Magnet Motors High power devices such as motors cannot be driven directly by the PIC (see course pack I on motors) High startup current!

  13. MotoMaster Motor DriverDesigned by Alex Simpkins of UCSD PWM Control for Speed • Transistors are much more efficient in on or off state than intermediate “op-amp” state • Pulse Width Modulation pulses the voltage on and off much more quickly than the motor can respond, resulting in an effective average voltage based upon duty cycle H-Bridge for Bi-directional Control

  14. Relays Mechanical switch activated by an electromagnet, thereby switching large current with only a small current input Disadvantage: Much slower than transistors, so PWM control is not possible Advantage: No voltage drop as with most H-bridges transistors

  15. Hands-on Guidelines for Good Circuit Implementation

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