Electronic Devices for the Mechanical Experimenter*Electronic Devices for the Mechanical Experimenter*

Nathan DelsonNathan Delson

*Title inspired by book, Mechanical Devices for the Electronics Experimenter

MEs are Responsible for More and More EE Design

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.

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.

Good Electronic Design vs. Bad Electronic Design

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”

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”

Like with ME Components, EE Components have input, output, and

power specs

Like with ME Components, EE Components have input, output, and

power specsExample 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

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

Categories of EE ComponentsCategories of EE Components

High Power vs Low Power

Analog vs Digital

Microprocessor

On/Off switch

Potentiometer

Optical Sensor

LED

Motor

Categories of EE ComponentsCategories of EE Components

High Power vs Low Power

Analog vs Digital

Microprocessor low power digital

On/Off switch low power digital

Potentiometer low power analog

Optical Sensor low power either

LED low power either

Motor high power analog

Light Emitting Diode (LED)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

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

Microprocessor: The 16F877A PIC on the X2 Board

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.

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.

Input Switch – INCORRECT MethodInput Switch – INCORRECT Method

Input Switch Correct Method: Avoids Floating Input

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.

Brain teaser: Can you connect switch so signal to PIC is low when switch is closed, and high when switch is open.

PotentiometerPotentiometer

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

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

voltagemeasuringdevice

5VDC

R1

R2

I1

I3V2

V1

I2

poteniometer wiper

DC Permanent Magnet MotorsDC Permanent Magnet MotorsHigh power devices such as motors cannot be driven directly by the PIC(see course pack I on motors)High power devices such as motors cannot be driven directly by the PIC(see course pack I on motors)

High startup current!

MotoMaster Motor DriverDesigned by Alex Simpkins of UCSDMotoMaster 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

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

RelaysRelays

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

Hands-on Guidelines for Good Circuit Implementation

Hands-on Guidelines for Good Circuit Implementation