e004020.pdf

COMPU TER

Input/Output for PCs

Hardware design by D. Aggelos

Here’s a simple project with Windows control software that allows you to

control up to eight relays or other actuators, and read back an equal

number of input lines, all by means of the parallel port on your PC.

12V

The UPIO software and hardware (a

board attached to the PC’s parallel port)

allows you control up to eight relay out-

puts using a Windows-style user interface

designed for user-friendliness. UPIO also

allows you read back logic states on input

lines.

IC4b

12V

IC2

RE1

D11

78L05

IC4c

22 Ω

1N4001

IC4d

12V

D1 0

IC4e

RE2

100µ

25V

100n

IC4f

22 Ω

Circuit description

The circuit that belongs with the UPIO

program is very simple and consists of a

few low-cost and easy to ﬁnd parts. The

circuit diagram is given in Figure 1. A tri-

state buffer type 74HCT241(IC5) arranges

all input contact reading. An 8-bit latch

type 74HCT574 (IC3) is used to preserve

the output state during instruction exe-

cution. The third essential component is

a power driver type ULN2803 (IC1) which

enables output relays Re1-Re8 to be actu-

ated and de-actuated.

Because the LPT input port consists of

just four bits (one nibble), two subsequent

readings are required from the HCT241 to

obtain the whole (8-bit wide) input word.

Supply power comes from an external

mains adaptor with an output of approxi-

mately 12 volts DC. An on-board regula-

tor type 78L05 (IC2) provides the HCT

and LS ICs with a 5-volt supply rail. Note

that the ULN2803 and relays are powered

from the unregulated 12-V supply. Obvi-

ously, the mains adaptor should be able

to supply the necessary current (all relays

may be actuated at the same time!).

12V

IC4 = 74LS05

12V

RE3

K11

IC4a

22 Ω

IC3

1N4001

74HCT574

12V

K10

470µ 25V

RE4

STROBE

+VS

22 Ω

12V

IC1

RE5

ULN

2803

22 Ω

VEE

12V

RE6

IC5a

R10

4x 10k

22 Ω

K13

12V

RE7

C10

C13

22 Ω

12V

4x 22n

RE8

IC5b

R11

4x 10k

22 Ω

K12

C15

C14

IC3

IC4

IC5

100n

IC5 = 74HCT241

4x 22n

002011 - 11

Figure 1. UPIO circuit diagram.

Elektor Electronics

4/2000

Universal Parallel

COMPU TER

The PCB

The PCB for this project was redesigned

to reﬂect Elektor style and standards from

artwork originally supplied by the author.

The resulting design is shown in Fig-

ure 2. The ready-made board is available

through our Readers Services as item

002011-1.

A PCB-mount ‘blue ribbon’ 36-way Cen-

tronics socket is used at the input to

allow easy connection to your PC’s

printer port. At the ‘output’ side of the

board, 3-way screw terminal blocks (con-

nected directly to the relay contacts)

allow the user to select N.C. (normally

closed) or N.O. (normally open) type con-

tacts. The digital inputs are divided over

two 4-way SIL connectors, K12 and K13.

Tailor-made

process control

Originally, the author supplied rather sim-

ple control software. By means of a ‘pro-

gram-style file’, created by the applica-

tion, it was possible to produce a simple

‘Output Flow’ with user-deﬁned timing. In addition,

output states could be checked by reading up to

eight contact-type inputs. Together with the output

control this allows ‘Hold’ or ‘One-Shot’ action to be

implemented, both are well-established features in

ﬂow control systems.

COMPONENTS LIST

K12

Resistors:

R1-R8 = 22 Ω

R9 = 820

IC1

IC2

Ω

R10,R11 = SIL array 4 x 10k Ω

D10

R11

K11

K13

C10

C1 1

C12

C13

IC3

Capacitors:

C1 = 470 µ F 25V radial

C2 = 100

IC4

C14

F 25V radial

C3,C4,C5,C14,C15 = 100nF

C6-C13 = 22nF

R10

K10

002011-1

Semiconductors:

D1-D8 = 1N4148

D9,D11 = 1N4001

D10 = LED

IC1 = ULN2803

IC2 = 78L05

IC3 = 74HCT574

IC4 = 74LS05

IC5 = 74HCT241

Miscellaneous:

K1-K8 = 3 way PCB terminal

block, raster 5mm

RE1-RE8 = PCB mount relay, 12V,

e.g., Siemens V23040-A0002-

B201

K9 = 2-way PCB terminal block,

raster 5mm

K10 = 36-way Centronics

connector, PCB mount

K11 = 3-way SIL pinheader with

jumper

K12,K13 = 4-way SIL-header

PCB, order code 002011-1 , see

Readers Services page and

Elektor website.

Disk, contains all project software,

order code 002011-11 , see

Readers Services page and

Elektor website (free download

for subscribers)

Figure 2. PCB design for the UPIO hardware (board available ready-made).

4/2000

Elektor Electronics

COMPU TER

Talking to ports

under Windows 95/98/NT

Having played around with the original software for

a while it was felt that this was rather unrefined

and unreliable. So our staff designer Luc Lemmens

set out to write an improved control program for the

UPIO hardware. Let’s look at the underlying prin-

ciples.

Under DOS and Windows 3.1, it used to be rel-

atively easy to control PC hardware directly using

higher programming languages like BASIC or Pas-

cal. All that was needed at that time was the odd

IN/OUT instruction in BASIC, or its PORT equiva-

lent in Pascal.

erties used in the example program (a

Delphi 2 application) will be given below.

not be edited because the LPT compo-

nent is missing. Also, because of various

problems we do not recommend using

the original ‘.exe’ ﬁle.

As a matter of interest only, the circuit

diagram was originally designed using

‘Protel’ schematic capture, while

‘Advanced Schematics’ software was

used for the PCB design. Both the circuit

diagram and the PCB artwork were

redesigned by Elektor Electronics for the

purpose of this article.

The really essential procedures are Open-

Driver and CloseDriver which, you

guessed it, open and close the TVicport

respectively. The logic variable (property)

ActiveHW flags if the port is open or

closed, or, in actual fact, if the driver is

available or not.

The property LPTNumPorts indicates

the number of printer ports in the system,

while LPTNumber determines which LPT

is being controlled by the driver. Finally,

LPTBaseAddress shows the base address

of that particular port. The component

also has a property called Pin , an array of

25 logic variables (bits) representing the

logic levels (states) found on hardware

port pins. By means of this array pro-

grammers have easy access to the pins

on the printer port. You only have to be

cautious which pin is input or output

only, or bi-directional.

(002011-1)

Design and software editing: L. Lemmens

Text editing: J. Buiting

Figure 3. Screendump showing the UPIO

control software in action.

HWTest and

the example program

The HWTest program as supplied on the

project disk illustrates the practical use of

this component in many ways. In fact,

we’d say it is a perfect starting point for

your own applications.

Naturally the example program (also

supplied on disk) was derived from

HWTest. The 8 relays on the UPIO board

may be switched on and off by ticking the

relevant boxes. The ticks in the panel

below the relay boxes indicate if a digital

input is high or low. If the PC contains

several printer ports, the thumbwheel

switch allows a different port to be

selected. As a matter of course, the

printer port control will only work if the

driver has been successfully loaded by

pressing the ‘Open Driver’ button. A

screendump of the UPIO control program

is shown in Figure 3.

In later versions of the Windows GUI, (release

95 and later), the user is increasingly ‘isolated’ from

the hardware, and it is no longer possible (and even

forbidden under Windows 95) to communicate

directly with various registers and memory loca-

tions. This kind of ‘Smalltalk’ is completely left to

the operating system in conjunction with various

device drivers. Writing your own device drivers is

arduous to say the least, so it is often better to go

on the Internet and see if someone else discovered

the wheel for you. In this case we landed at

www.entechtaiwan.com where we found a (share-

ware) LPT component called TVicPort written by

Victor Ishikeev. This component is available in ver-

sions for Delphi (version 2 through 5), Java Builder

(version 1, 3 and 4), Visual BASIC (version 6), Bor-

land C++ and MS Visual C++ in Windows 95/98

and Windows NT.

As could be expected in this day and age of

object-oriented programming, the printer port is no

more than an object with all sorts of properties and

responding to all sorts of events . Using this concept

the programmer has easy access to the object (in

this case the printer port), while control is exerted

via methods associated with the relevant compo-

nent. A brief discussion of the methods and prop-

Tools used for the project

For the original UPIO.exe application, the

author used Borland Delphi development

environment (Version 1-16 bits), which

generates the ‘.dpr’ application program

files, the ‘.pas’ unit files, the ‘.opt’ and

‘.res’ files. All original files for the UPIO

project, as well as the refurbished version

of the control software may be found on

a ﬂoppy disk with order code 002011-11.

It should be noted that the source code

file as we received it from the author is

supplied ‘for information only’ — it can

Elektor Electronics

4/2000

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