e003X10.pdf

Java is a world language. Many people think that this pro-

gramming language, which was developed by Sun

Microsystems, is only suitable for embellishing Internet pages

with cute applets. Nothing could be further from the truth.

Java is a fully-fledged programming language that can be

used for making Internet applets and stand-alone applica-

tions for all possible platforms. What about a Java applica-

tion in a ring, a credit card or your toaster? It’s all possible!

By G. Polder

Java MultiMeter (JMM)

handy software for RS232 multimeters

in the past. In addition, the information

in the log window can be stored for

subsequent processing, for example

using a spreadsheet program.

If you click on ‘Plot’, a plot window

appears that displays the measured

values in graphic form. This plotting

function works in a fairly advanced

manner. The scale is automatically

adjusted after each new measurement

point is added. You can use the mouse

to draw a rectangle over part of the

plot, and then zoom in by moving the

mouse down and to the right, or zoom

out by moving the mouse up and to

the left. If you press the ‘Fill’ button, the

full set of data is displayed again. Sev-

eral plot windows can be open at the

same time. New measurement data

are always entered in the most recently

opened window.

Figure 1. The main window of Java MultiMeter shows the settings of the multimeter con-

nected to the PC, and the measured value in the form of a number and a bar graph.

The buttons can be used to manually make a new measurement or enable the pro-

gram to automatically read in measurements at a regular interval.

Operation

Java is an object-oriented language.

This means that the programmer makes

objects that communicate with each

other and that are ‘semi-concurrently’

active. The most important objects in

JMM are the following:

In this project, Java is used for reading

data from a multimeter that has an

RS232 port (such as the Voltcraft model

3850d). For more background informa-

tion on this type of multimeter, see the

April 1997 issue of Elektor Electronics .

Java MultiMeter (JMM) has a very sim-

ple design. The main window displays

the measurement value, the range and

a bargraph (a semi-analogue mea-

surement bar), plus a number of but-

tons. The READ button at the lower right

is used to read in a value, while the

START and STOP buttons can be used to

control repetitive measurements at an

adjustable interval that can be set

using a slider (Sequence).

Up to now, this is nothing unusual. How-

ever, there is more. At the top of the

window there is a menu bar that has

two options in the Window menu,

namely ‘Plot’ and ‘Log’. If you click on

‘Log’, a logging window appears that

displays all measured values and the

time of each measurement. This can

be useful for looking at what happened

➧

the main object, which contains the

measurement data, the buttons and

a timer that periodically sends a ‘D’ to

the RS232 port if it is enabled;

➧

an RS232 receiver object, which col-

lects RS232 data and sends the entire

string to the main object after it

receives a <CR>(Carriage Return)

sequence;

➧

a log object, which receives mea-

surement strings from the main

10 - 3/2000 Elektor Electronics EXTRA —————————————— PC T OPICS

Figure 2. The log window displays a summary of all measure-

ments, with their associated dates and times.

Figure 3. The plot module shows a graphic diagram of the

most recently measured values. Several plot windows can be

open at the same time.

object, attaches date and time infor-

mation to them and organises them

into a list;

ful Java programming environment;

on the Elektor CD-ROM PC Software 98-

99 (ISBN 90-5381-106-0).

➧

Solutions Consulting serial port soft-

ware: these are Java classes (rou-

tines) and Windows DLLs that allow

Java to make use of the RS232 ports

of the computer;

(002010-1)

➧

plot objects, among which the most

recent object graphically displays the

data that are received from the main

object.

The program JMM won the third prize in the

Netherlands division of the PC software com-

petition organised by Elektor in June 1998. All

winning entries for this competition are col-

lected on the above-mentioned CD-ROM.

➧

PT-Plot: a Java plotting package.

Required hardware

One of the features of Java is that it is

platform-independent. This is achieved

by running Java programs on what is

called a Java Virtual

Machine. With Visual

Cafe, it is possible to

combine the Java

programs with the Vir-

tual Machine into a

single .EXE file. JMM

utilises this capability.

This however means

that a number of

Semantic DLLs must

be installed. An instal-

lation program for

these DLLs, which also

includes the remain-

ing components of

JMM, may be found

The demands placed on the computer

are not particularly high. It must of

course be a PC that runs under Win-

dows 95/98 or Windows NT.

In addition, a digital multimeter with an

RS232 port (such as the Voltcraft model

3850d) is needed to provide the mea-

surements to the computer via a serial

channel. Finally, a suitable RS232 cable

is needed to interconnect the meter

and the computer.

Required files

jmm.exe

The Java MultiMeter program.

csall

This folder contains a number of Solutions

Consulting serial port DLLs.

Place these DLLs in the folder c:\windows\sys-

tem32 (for Windows 95/98)

or c:\winnt\system32 (for Windows NT).

snjrt20.exe

Installation program for Semantic Java run-

time DLLs.

The software

libwin95

Property files for Windows 95/98.

Copy these files to the folder c:\windows\sys-

tem\lib.

The software was produced using the

following software packages:

libwinnt

Property files for Windows NT.

Copy these files to the folder c:\winnt\sys-

tem32\lib.

➧

Symantic Visual Cafe: this is a power-

The serial protocol

Programming the communications between the PC and a digital mul-

timeter with a serial interface is fairly easy if you use a high-level pro-

gramming language such as Visual BASIC, Visual C ( Java ) or Visual

Pascal ( Delphi ).

To start with, the serial interface that is used must be initialised. For most

DMMs, it should be configured to 1200 bps, no parity bit, 7 data bits in

ASCII format, 2 stop bits and software handshaking. This completes the

preparations for transferring measurement values. All that the comput-

er or program has to do now is to request a measurement value. This is

done by sending the character ‘D’ (#68) to the DMM. In response, the PC receives a string of characters that contain the current measure-

ment value, the unit and the measurement range. The received string is 14 bytes long, as shown in the figure below. The DMM models 506

and M-3860M are exceptions to this rule. The latter model works at a data rate of 9600 baud and always sends the measurement values

for the main display and the three auxiliary displays as a single data packet that is 56 bytes long. The model 506 works at 1200 baud, but

it sends a data packet whose length varies between 6 and 15 bytes. All DMMS are rather slow in operation; new measurements are sent to

the PC no more often than once every 0.5 second.

4567890

1234

example 1:

DC –16. 23

mVCR

example 2:

3 . 999M

O H M CR

measurement

range

measured value

unit

end

recognition

970035 - 15

PC T OPICS ————————————— Elektor Electronics EXTRA

11 - 3/2000

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