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CircuitSim v1.9.1

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Basic circuit simulator with many built-in components. Check out src/com/ra4king/circuitsim/simulator/components for examples of how Components are written. Their GUI counterparts are in src/com/ra4king/circuitsim/gui/peers.

Screenshot Screenshot


The provided gradle scripts can be used to easily build a JAR file. Just run /.gradlew jar on Linux or /.gradlew.bat jar on Windows!

The release directory contains a script that automatically builds the JAR, and generates an executable image for Windows, Mac, and Linux.



  • Hotfix for ROM component not saving its contents to disk.


  • The grid background can now be hidden: View -> uncheck Show grid
  • Circuits can be exported as image files: File -> Export as images
  • New component: 7-segment display
  • Updated components: probes and constants can now display in multiple formats.
  • Integer inputs now accept multiple formats: decimal, binary, and hex
  • RAM and ROM editors have been improved, and ROM edits now support undo and redo.
  • Remove the ability to negate the NOT gate's input, this looks to have been an oversight.
  • Improve placement and display of gates with negated inputs and more than 5 inputs: no more "floating" inputs. Inputs are now either directly attached to the gate's body or have a line linking them to the gate. This is backwards compatible by maintaining the previous behavior for older save files.


  • New component: Breakpoint component that automatically stops the clock at a particular input value
  • New component: Power and Ground components that are pretty much just the 1-bit constants 1 and 0 respectively
  • Fixed a deadlock issue in Clock
  • Fixed possible race conditions where the circuit was modified while it's being accessed outside the simulator lock


  • Hotfix for an issue that leads to erroneous Short Circuit messages when there are none


  • RAM now has the option to have separate load/store ports
  • The transistor has been updated with a more accurate version. This is backwards compatible by deprecating the old transistor and replacing it with a new component


  • Hotfix for issue with buffer component where setting a label causes a NullPointerException
  • Hotfix for issue with memory editor for both RAM and ROM components where pasting 16 or more values causes it to skip a column every 16th value
  • Improve error message window to include "Save and Exit"


  • Significant performance and memory usage improvements
  • Holding CTRL will keep a component selected after placing it
  • Circuit file generation is now deterministic
  • Fix subcircuit pin count mismatch errors
  • Fix display of Output pin, where it used to be printed as Input pin
  • Fix saving ROM contents after being broken in 1.8.0
  • (Breaking change) Fix subcircuit pin ordering on the east and west side by sorting by Y instead of X


  • Revamp ROM/RAM component look: now showing the current address and value
  • Revamp ROM/RAM memory editor: no need to double click to start typing, no need to hit enter to commit, full multi-cell copy/paste support
  • Huge improvement and bug-fixes to wire behavior when moving components and with undo/redo
  • Add RandomGenerator component
  • Add copy/cut/paste to context menu in circuit editor
  • Display missing label names in certain components
  • Add All Files option in Load File dialog
  • Fixed bug with gates where downsizing the number of inputs kept the extra Negate options


  • Fix several bugs with wire creation when dragging components
  • Give an option to send an error report upon unexpected errors
  • Minor bug fixes


  • Fix blue wire issues with Tunnels and subcircuits
  • Highlight wires when clicking on them
  • Ctrl+scroll now zooms in/out
  • Right clicking when placing components or dragging wires cancels the action
  • Fix bug with intersecting wires being auto-joined on drag
  • Improved error handling


  • Add Probe component, which lets you observe values on wires without resorting to output pins
  • Improve behavior multi-component selection when holding down control by disabling drag-less wire creation when control is held down
  • Copy doesn't do anything when nothing is selected instead of emptying the clipboard
  • Other minor bugs fixed


  • Squashed tunnel bugs: now short-circuits should propagate properly across them and tunnels should work properly
  • Added comparison type to Comparator: now you can do both 2's complement and unsigned comparison
  • Draw magnifying glass to subcircuit components when hovering over them to indicate ability to view internal state
  • Officially making a file format change supporting library paths
  • Other minor bugs fixed


  • Big thanks to Cem Gokmen for helping with the Mac issues and Austin Adams for gradle-ifying the repo!
  • Now supporting both Java 8 and 9 - thanks to Austin Adams for figuring out how to create a multi-release Jar
  • Huge rendering performance improvements, especially for Mac
  • Fixed keyboard shortcut issue on Mac
  • Use system menu bar on Mac instead of the in-app bar
  • Added an update checker that notifies you when there is a new version
  • Fixed a bug with subcircuits where it pushed values through output pins, causing seemingly un-explainable short circuits
  • Improved behavior of tab selection when moving them or deleting them, especially with undo/redo
  • Many minor bug fixes and improvements


  • Fixed exceptions being thrown when using Tunnels
  • Now you don't have hit enter to update a text or value property, someone complained that it was annoying. The component is automatically updated when you unfocus from the text input
  • Multi-bit wires with a floating bit (X) now show up as dark blue instead of black
  • Button now has directions


  • Improved behavior when dragging components to also delete wires whenever they overlap existing ones
  • Huge performance increases with subcircuits and tunnels. Bad designs will still be very slow to run the autograder in
  • Now showing Help dialog on first run


  • Added creation of new wires when dragging components. This allows maintaining existing connections when dragging components to new locations
  • Hold CTRL before beginning the drag to disable this
  • Fixed file load issue where an error was thrown if the folder doesn't exist anymore
  • Fixed issues with dragging + keyboard shortcuts
  • Fixed an undo bug when updating components