[Ørsted-DTU] [DTU / Technical University of Denmark]
• Uplinks at bottom of page

Javalab Java icon

• Javalab circuit examples
• How to use Javalab
• About Javalab opamps
• Technical notes
• Javalab download

 
Javalab is a collection of Java based circuit simulations. Javalab is intended as a supplement to the teaching of basic electronic circuit theory. Javalab is interactive in the sense that the student for a given circuit is able by very direct means to adjust signal and component values - as by turning a knob or dragging an old-fashioned slide resistor in the real lab - and to observe immediately the circuit response, i.e. all relevant currents and voltages. Javalab cannot, however, as regular simulation tools (e.g. PSpice) modify the circuit topology, i.e. add or remove circuit components.

Recognized as a distinguished, high-quality source of learning material by MERLOT (2002.05.28)

[www.merlot.org]

Annotated as a National Science Digital Library Report Selection (2002.06.07)

[scout.cs.wisc.edu]


Javalab circuit examples

 Voltage divider  Thevenin equivalent, available power.
 Current divider  Norton equivalent, available power.
 Heating elements  Four power levels with two resistors.
 Wheatstone bridge  Slightly larger resistive circuit.
 Ladder network  Alternating series/shunt resistors.
 Resistor cube  Circuit with many nodes!
 Voltage follower  OpAmp as the only component.
 Inverting amplifier  Standard opamp circuit.
 Bridge amplifier  Slightly larger opamp circuit.
 Negative resistance  OpAmp two-terminal circuit.
 Controlled current source  OpAmp circuit with infinite output resistance.
 D/A converter  Multi-purpose summation amplifier.
 Schmitt trigger  OpAmp with positive feedback.
 Rectifier bridge  Standard 4-diode circuit.
 Voltage regulator  Standard Zener diode circuit.
 Diode AND-OR gate  Circuit with many diodes.
 npn Transistor inverter  Simple common-emitter stage.
 npn Transistor biasing  General common-emitter bias circuit.


How to use Javalab

Interaction with the Javalab applets is implemented by component scrollbars and radio buttons (switches). All scrollbars have 100 steps between min and max values. Clicking a scrolbar arrow or dragging the scroll box makes a move of 1 step at a time. Clicking between the scroll box and one of the arrows makes a single move of 10 steps. Wait for "Circuit ready" in the status line before each next move.

Voltages in the Javalab applets are generally shown as node potentials with reference to a ground node. The actual direction of a current results as a combination of convention (arrow direction) and notation (sign). Check for your exercise the component relations, e.g. Ohm's law, as well as the Kirchhoff rules. Try to predict at least the qualitative reactions of the circuit upon any planned adjustment of signal or component values.

Be aware that illegal circuit configurations will lead to strange results, inconsistent results, or indefinite results. Illegal configurations are for instance a shorted voltage source or a closed circuit loop containing zero resistance. Some of the more complex circuit examples may respond with indefinite results even in cases of quite legal zero-resistance configurations (trivial exceptions not always programmed in detail!).

Please report by email any observed errors or ambiguities in the Javalab examples. Also, feel free to propose ideas for additional circuit examples.


About Javalab opamps

The classical ideal operational amplifier is characterized by infinite input impedances (zero input currents), zero output impedance (ideal voltage source output), and an infinite open-loop voltage amplification factor, A. The Javalab opamps have been slightly refined by introducing finite values of A. In order to allow for a great dynamic range, the A factor is given in dB (decibels) = 20·log(A). For instance, 100 dB corresponds to A = 100000, whereas 0 dB corresponds to A = 1.

OpAmps with very large A factors (100-120 dB being quite normal) and a surrounding negative-feedback circuit (a circuit path between the output terminal and the inverting input terminal) will lead to the simplification known as the virtual-ground principle: The output voltage remains finite, whereas the input voltage difference is suppressed by the feedback mechanism to virtually zero! The Javalab option of an adjustable A factor makes it possible to watch the gradual transition from an extremely poor opamp to the classical ideal opamp - and hence to be convinced of the consistency of the virtual-ground principle.

The output voltage of any real opamp will of course be restricted by the limited supply voltages of the opamp. The situation arising from an attempt to exceed these restrictions is named saturation. Javalab opamps are generally programmed to saturate at output voltages of ±10 V.


Technical notes

Regretfully, the remarks below most of all resemble a general disclaimer. One of the prominent features of the Java language was supposed to be the basic idea of platform independency. Consequently, all of the Javalab web pages should easily qualify to bear the banner: "Best Viewed With Any Browser". Unfortunately, the real world of browsers and Java interpreters apparently makes life less simple than that!

Javalab applets have been developed by means of Sun's Java Development Kit JDK1.2 and tested with Netscape 4.5 for Windows 95, with screen resolutions of 800 x 600 and 1024 x 768 pixels. Higher resolutions combined with relatively large font sizes may not leave sufficient space in the applet text labels to display a possible minus sign in front of a number! Certain browsers are not able to display special characters in applets (Unicode). Older browsers, although containing a Java interpreter, may give the fatal message: "Applet can't start .. got a security violation ..". Update your browser, or see Java™ Plug-in Product concerning Sun's Java Runtime Environment (JRE).

Please report by email any other observed technical problems with the Javalab applets. Please include information about browser version, etc.


up to top of this page      up to ES-home      up to Ørsted-DTU      up to DTU (Technical University of Denmark)

Visitors since: 1999.04.29
Long list / Latest 100
OBS counter reset: 2002.03.19
from 10551 to 0
Latest update: 2003.10.27
Lars Drud Nielsen, ldn@oersted.dtu.dk
[Valid HTML 4.0?] [Best Viewed With Any Browser]
[Opdatering af log]