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Javalab
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Javalab circuit examples |
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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) | Annotated as a National Science Digital Library Report Selection (2002.06.07) |
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. | ||
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.
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.
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.
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