ElectroSim 2.0
Interactive Simulations of Basic Electronic and Operational Amplifier Circuits

Tom O'Haver, Professor Emeritus

Department of Chemistry and Biochemistry
The University of Maryland at College Park

Created November 1996, Last updated November, 2013
A Links2Go Key Resource Award in the Simulation Models topic.
A StudyWeb 4-star site.

[Instructions]  [List of circuits]  [User Feedback]  [Homework assignments]  [Related software]  [Other good sites]

Ohm's Law

Series resistors

Parallel resistors

Wheatstone bridge

Simple Zener-regulated power supply

Transistor switch driving a relay

Common Emitter AC Amplifier

Operational amplifier without feedback

Voltage Follower

Non-inverting amplifier

Inverting amplifier

Signal current flow in inverting amplifier

Effect of open-loop gain

Input resistance of a non-inverting amplifier

Adder (summing amplifier)

Subtractor (Difference amplifier)

Photodiode photometer



Voltage follower with transistor
output current booster

Programmable current driver with
transistor output current booster

This is a collection of real-time, theory-based interactive simulations of some simple electronic circuits for use by students in a course I used to teach called "Electronics for Chemists" at the University of Maryland College Park, which was basically a laboratory course in elementary practical instrumentation electronics. I used them as homework assignments, while the students were constructing and studying these circuits in the laboratory, in an effort to deepen their conceptual understanding. A Macintosh computer lab in the building allowed all students access to these programs, and, once the Internet became available to the campus in the early 90's, they were also available on-line.

One of the problems in teaching electronics is the difficulty students have in moving back and forth between the static, two-dimensional symbolic representations of traditional schematic diagrams and the real, 3-dimensional circuits in the laboratory. My simulations help to bridge this gap by allowing the student to work with representations that look just like the schematic diagrams in their textbooks, yet actually work and respond to changes just like the real circuits. Using the mouse, you can drag sliders to control voltages and resistances, open and close switches, and type in the values of various components. The simulations use the laws of electricity (Ohn's Law, Kirchoff's Laws, etc) to display voltages and currents throughout the circuit dynamically in real time as the sliders are moved.

Another problem is that so much is invisible. The actual laboratory experiments show only the outer, macro-level effects, leaving the student to imagine the inner workings such as current flows and voltages changing at multiple points in a circuit. Computer simulations can sometimes show these inner workings in a way that real experiments can not. Still, these computer simulations were not intended to replace laboratory experiments and real-world experience, but rather to extend and augment textbook treatments. Real circuits display a host of other effects that are not included in these simulations, such as overheating, burnout, component failure, poor shielding and grounding, intermittent and unstable connections, noise, drift, and stray pickup.


These simulations do not run on the Web; they are self-contained programs that can be downloaded and run on stand-alone machines. They were developed in HyperCard for the Macintosh in the early 1990s, but there are also versions for PCs and Unix machines.

If you have a old Macintosh model, you can download and run the original Hypercard stacks. They are very small and require little computer power or screen space; you can have several of the simulations open at the same time in separate windows. They'll even run on the old 9" monochrome Macs such as the SE or Classic. Click here to download the complete set of ElectroSim 2.0 modules in ".sit" compressed format (570 KBytes), including the Hypercard Player application. Stuffit Expander will automatically decode and decompress the downloaded file into a folder containing the full set of ElectroSim modules. Double-click on a module to launch it, or drag and drop it onto the Hypercard Player.

PC users and others can run these simulations via the free downloadable Revolution Dreamcard Player, which is available for several platforms. To download the complete set of ElectroSim modules for a Windows PC, including the player, right-click on this link and select "Save Link As..." to begin the download (5.5 MBytes) to your PC. Then right-click on the ElectrosimRevolution.zip file and select "Extract All...". Open the resulting ElectrosimRevolution folder and install the Dreamcard Player by double-clicking on "dreamcardplayersetup.exe" and following the on-screen instructions. Multiple simulations may be open at one time. Thanks to Phil Odor (jpodor@f2s.com) for his excellent work in converting my Hypercard stacks to Revolution Dreamcard format.

If you have trouble installing the DreamCard player, you can also run these simulations with the free StackRunner from http://www.sonsothunder.com/devres/livecode/downloads/StackRunner.htm.  Open each simulation by right-clicking on the corresponding *.rev file in the ElectrosimRevolution folder and selecting "Open with..."  > "StackRunner...".  Multiple simulations may be open at one time.

 On the left side of each simulation module is a panel with several icons. Click on:

   "What do I do?" for quick instruction for that module.
   "Explain" to pop up a series of text boxes that explain the circuit operation (click again to hide the boxes).
   "Show current flow" to see an animation of current flowing.
   "Show specs" to inspect and edit the transistor's characteristics.

next Click this icon to view the next simulation. Click this icon index to return to this index page.

Homework assignment for the operational amplifier simulations

Other related software

Interactive Computer Models for Analytical Chemistry Instruction
SPECTRUM: a Student Tool for Digital Signal Processing in Chemical Analysis
Introduction to Signal Processing in Chemical Analysis

Unsolicited Comments from Users

" ... a fantastic website that reinforces the theory that we are studying by actually letting a beginner see what is actually happening."

"WOW! It is a GREAT pleasure to find such content on the WWW."

"I found your site last week and have already started using it in two of my classes."

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" ... lots of useful stuff."

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"Just wanted to say how very useful they were to me."

"I have found your interactive simulations of basic electronics extremly interesting."

" ...I'm writing to offer our thanks for your Hypercard models. The transistor models have helped us dredge old knowledge back to the surface...."

Other good electronics sites

Links checked and corrected November, 2013.
  1. The A-Z Top Electronics/Electricity Tutorials
  2. Basic electronic design build and test for beginners, students, teachers, hobbyists
  3. Design Electronics complete introductory electronics course
  4. Electronics: An Online Guide for Beginners
  5. Elementary Electricity 01
  6. Virtual Oscilloscope Simulation

Links2Go Key Resource Award in the Simulation
        Models topic This page was created by Prof. T. C. O'Haver , Department of Chemistry and Biochemistry, The University of Maryland at College Park. Comments, suggestions and questions should be directed to Prof. O'Haver at toh@umd.edu. First version created in 1996. Last updated November 2013.
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