introductory interfacing & electronics

ACSE Conference 11/2004

Intro. Interfacing & Electronics 1

Introductory Interfacing & Electronics

Peter [email protected]

Presented at Durham CollegeNovember, 2004



Overview This presentation covers a basic

introduction to interfacing with the parallel port and just enough electronics to keep you from damaging your computer.



Interfacing Introduction



Interfacing Overview

Computer Interface Peripheral

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

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



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



Identifying the Parallel Port It’s the female connector with

25 pins “DB25”

Can be on a card



Electronics Introduction



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 ()

Limits the amount of current



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)



Voltage Sources



Current Is the flow of electrons

Direction depends on convention

Conventional Current Flow (+) to (-)

Electron Current Flow (-) to (+)



Ohm’s Law

R

VI

“Current (I) is proportional to Voltage (V) and inversely proportional to

Resistance (R)”

RIV I

VR



Ohm’s Law & Power Wheel

Reproduced by permission of Tony van Roon, 2002 http://www.uoguelph.ca/~antoon



Kirchhoff’s Laws Kirchhoff’s 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 Kirchhoff’s Current Law

“The current entering a junction must equal the current leaving the junction”

Use in parallel circuits.



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…



Resistors Can be rated by…

Resistance (Ohms, ) Tolerance (% of nominal value) Power Rating (Watts)

Schematic Symbol…



Resistor Types



Resistor Colour Code

Reproduced by permission of Tony van Roon, 2002 http://www.uoguelph.ca/~antoon



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

= 3.3 k



Resistor Power Ratings



Series Circuits

...21 RRRT

One current path, therefore the current is the same everywhere

Total resistance is the sum of the individual resistances



Parallel Circuits

...21 IIIT

More than one current path Total current is the sum of the

individual currents



The Parallel Port – The Hardware



Parallel Port Specifications Output Voltage

0V for “low” 5V for “high” TTL (Transistor-Transistor Logic)

Output Current Limitation 10-15 mA (careful!)



Parallel Port Pinout

Graphic from http://www.doc.ic.ac.uk/~ih/doc/par/



Output Table

Pin # Label Bit Value2 D0 20 = 13 D1 21 = 24 D2 22 = 45 D3 23 = 86 D4 24 = 167 D5 25 = 328 D6 26 = 649 D7 27 = 128



Input Table

Pin # Label Bit Value15 S3 23 = 813 S4 24 = 1612 S5 25 = 3210 S6 26 = 6411 /S7 27 = 128



Interfacing an LED Circuit

D0

D6

D5

D4

D3

D2

D1

D7



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



Doing the Math

LEDRT VVV

150

020.0

3

A

VI

VR

R

R

mAII LEDR 20

V

VVV LEDTR

3

25

R

R

I

VR

From Ohm’s Law

From Kirchhoff’s Voltage Law

Currents equal in a series cct



Motor Control

2N3904

TIP31

(A stepper motor would require more outputs)

D0

M

9V

E

BC



High Current ControlDC Voltage

Source

Relay

Use a relay



Parallel Port Connector Tip



The Programming



Turing: Preparing for Interfacing Turing is already prepared for

interfacing with the parallel port No preparation necessary!



Turing: Turning On the LED Parallelput(value)

Parallelput(1) turns on the 1 bit (D0)

Parallelput(255) turns on all bits (D0-D7)



Turing: Turning Off the LED Parallelput(0)



Turing: Flashing the LEDloop

parallelput (1)

delay (250)

parallelput (0)

delay (250)

end loop



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 forend loop



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);



Java: OutputParallelPort lpt1 = new

ParallelPort(0x378);

int byteVal = 255;

lpt1.write(byteVal);

System.out.println("Output toport: " + byteVal);



Java: InputParallelPort portIn = new

ParallelPort (0x378);

int in;

in = portIn.read ();

System.out.println (in + " is currently being input.");



Java Delay Methodprivate static void delay (int mS)

{

try {

Thread.sleep (mS);

}

catch (Exception e) {

;

}

}



Delphi: Preparing for Interfacing Download io.dll from

http://geekhideout.com/downloads/io.dll

Copy into project folder



Delphi: Outputprocedure PortOut(Port : Word; Data :

Byte); stdcall; external 'io.dll';

procedure TForm1.Button1Click(Sender: TObject);

begin

PortOut(888,1);

end;



Delphi: Inputfunction PortIn(Port:Word):Byte; stdcall;

external 'io.dll';

procedure TForm1.Button3Click(Sender: TObject);

var

InValue : Byte;

begin

InValue := PortIn(889);

label1.Caption := IntToStr(InValue);

end;



Delphi Delay Procedureprocedure xSleep(milliseconds:

LongInt); var iTemp : Longint;

Begin

iTemp:= GetTickCount + milliseconds;

while GetTickCount < iTemp

doApplication.ProcessMessages

End;



Assembler: OutputMOV DX,0378H

MOV AL,n

OUT DX,AL

Where n is the value you want to output.



Resources



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/delphi1.htm



Textbook References Computer Engineering: An Activity-Based

Approach (Holt) Networks, Interfaces and Integrated

Circuits (Holt)



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

A: Because DEC25 = OCT31



Contact Information Pete Beens

Westlane Secondary SchoolNiagara Falls, ONL2H1T5905.356.2401

Web: http://www.beens.org Email: [email protected]

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