Introductory Interfacing

1
Introductory Interfacing Electronics

• Peter Beens
• peter_at_beens.org
• Presented at Durham College
• November, 2004

2
Overview

• This presentation covers a basic introduction to
  interfacing with the parallel port and just
  enough electronics to keep you from damaging your
  computer.

3
Interfacing Introduction
4
Interfacing Overview

• Computer

Interface
Peripheral

• Wires
• ICs
• Resistors
• Capacitors
• Transistors
• Connectors

• LEDs
• Motors
• Lights
• Robots
• Joystick
• Music Box

5
What Ports Can We Interface?

• Parallel Port (AKA Printer Port)
• Serial Port (AKA RS232)
• Keyboard Port
• USB??? (Hopefully soon)

We will concentrate on the Parallel Port
6
Identifying the Parallel Port

• Its the female connector with 25 pins
• DB25

Can be on a card
7
Electronics Introduction
8
Three Main Invisible Electrical Properties

• Voltage, V, Volts
• Provides the push
• Current, I, Amperes (Amps)
• Flow of Electrons
• Amount of Current is dependent on Voltage and
  Resistance
• Resistance, R, Ohms (S)
• Limits the amount of current

9
Safe Current Voltage Levels

• Voltage 30 V
• Voltages inside a computer do not exceed 12 V,
  except at the power supply and power switch on
  older computers, which are at 120 V.Be careful
  in these areas!
• Current 5 mA (0.005 Amperes)

10
Voltage Sources
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Current

• Is the flow of electrons
• Direction depends on convention

12
Ohms Law
Current (I) is proportional to Voltage (V) and
inversely proportional to Resistance (R)
13
Ohms Law Power Wheel
Reproduced by permission of Tony van Roon, 2002
http//www.uoguelph.ca/antoon
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Kirchhoffs Laws

• Kirchhoffs Voltage Law
• The sum of the voltage drops equals the applied
  voltage, or
• The sum of the voltage drops around a closed
  loop equals zero
• Used in series circuits
• Kirchhoffs Current Law
• The current entering a junction must equal the
  current leaving the junction
• Use in parallel circuits.

15
Light Emitting Diodes (LEDs)

• A type of diode designed toemit light
• Can be visible or IR
• 2 V voltage drop
• Typically draws 20 mA (0.020 A)
• Schematic Symbol

16
Resistors

• Can be rated by
• Resistance (Ohms, S)
• Tolerance ( of nominal value)
• Power Rating (Watts)
• Schematic Symbol

17
Resistor Types
18
Resistor Colour Code
Reproduced by permission of Tony van Roon, 2002
http//www.uoguelph.ca/antoon
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Resistor Colour Code Example

• 1st band orange 3
• 2nd band orange 3
• 3rd band red 2 (i.e. 102)
• 4th band gold 5

33 x 102 3300 S 3.3 kS
20
Resistor Power Ratings
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Series Circuits

• One current path, therefore the current is the
  same everywhere
• Total resistance is the sum of the individual
  resistances

22
Parallel Circuits

• More than one current path
• Total current is the sum of the individual
  currents

23
The Parallel Port The Hardware
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Parallel Port Specifications

• Output Voltage
• 0V for low
• 5V for high
• TTL (Transistor-Transistor Logic)
• Output Current Limitation
• 10-15 mA (careful!)

25
Parallel Port Pinout
Graphic from http//www.doc.ic.ac.uk/ih/doc/par/
26
Output Table
27
Input Table
28
Interfacing an LED Circuit
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Understanding the LED Circuit

• The parallel port output is 5V
• A standard red LED needs 20 mA and drops about 2
  V
• A resistor is needed to drop the excess voltage

30
Doing the Math
From Kirchhoffs Voltage Law
From Ohms Law
Currents equal in a series cct
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Motor Control
(A stepper motor would require more outputs)
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High Current Control

• Use a relay

33
Parallel Port Connector Tip
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The Programming
35
Turing Preparing for Interfacing

• Turing is already prepared for interfacing with
  the parallel port
• No preparation necessary!

36
Turing Turning On the LED

• Parallelput(value)
• Parallelput(1) turns on the 1 bit (D0)
• Parallelput(255) turns on all bits (D0-D7)

37
Turing Turning Off the LED

• Parallelput(0)

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Turing Flashing the LED

• loop
• parallelput (1)
• delay (250)
• parallelput (0)
• delay (250)
• end loop

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Turing LED Walking

• loop
• loops up
• for i 0 .. 7
• parallelput (2 i)
• delay (500)
• end for
• loops down
• for decreasing i 6 .. 1
• parallelput (2 i)
• delay (500)
• end for
• end loop

40
Java Preparing for Interfacing

• Download http//www.geocities.com/Juanga69/parport
  /parport-win32.zip
• Extract the parport folder to your classes folder
• Copy parport.dll to you bin folder
• import parport.ParallelPort
• ParallelPort lpt1 new ParallelPort (0x378)

41
Java Output

• ParallelPort lpt1 new ParallelPort(0x378)
• int byteVal 255
• lpt1.write(byteVal)
• System.out.println("Output to port " byteVal)

42
Java Input

• ParallelPort portIn new ParallelPort (0x378)
• int in
• in portIn.read ()
• System.out.println (in " is currently being
  input.")

43
Java Delay Method

• private static void delay (int mS)
• try
• Thread.sleep (mS)
• catch (Exception e)

44
Delphi Preparing for Interfacing

• Download io.dll from http//geekhideout.com/downl
  oads/io.dll
• Copy into project folder

45
Delphi Output

• procedure PortOut(Port Word Data Byte)
  stdcall external 'io.dll'
• procedure TForm1.Button1Click(Sender TObject)
• begin
• PortOut(888,1)
• end

46
Delphi Input

• function PortIn(PortWord)Byte stdcall
  external 'io.dll'
• procedure TForm1.Button3Click(Sender TObject)
• var
• InValue Byte
• begin
• InValue PortIn(889)
• label1.Caption IntToStr(InValue)
• end

47
Delphi Delay Procedure

• procedure xSleep(milliseconds LongInt) var
  iTemp Longint
• Begin
• iTemp GetTickCount milliseconds
• while GetTickCount lt iTemp
• do Application.ProcessMessages
• End

48
Assembler Output

• MOV DX,0378H
• MOV AL,n
• OUT DX,AL
• Where n is the value you want to output.

49
Resources
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Web Resources

• http//www.epanorama.net/circuits/parallel_output.
  html
• http//www.lvr.com/jansfaq.htm
• http//www.doc.ic.ac.uk/ih/doc/par/
• http//www.southwest.com.au/jfuller/delphi/delphi
  1.htm

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Textbook References

• Computer Engineering An Activity-Based Approach
  (Holt)
• Networks, Interfaces and Integrated Circuits
  (Holt)

52
Q Why can't programmers tell the difference
between Christmas and Halloween?

• A Because DEC25 OCT31

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Contact Information

• Pete BeensWestlane Secondary SchoolNiagara
  Falls, ONL2H1T5905.356.2401
• Web http//www.beens.org
• Email peter_at_beens.org