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Circuits Maximus
Documentation
MIT 6.01 Introduction to EECS I

Contents

1  Getting Started
    1.1  What Is CMax?
    1.2  Installation
    1.3  Running CMax
2  Circuit Editor
    2.1  Adding Circuit Elements
        2.1.1  Resistors
        2.1.2  Wires
        2.1.3  Power Supply
        2.1.4  Voltage Probes
    2.2  Modifying a Circuit
        2.2.1  Moving Large Segments of a Circuit
    2.3  File Management
3  Circuit Simulator
4  Keyboard Shortcuts Reference
5  Changelog

1  Getting Started

1.1  What Is CMax?

Circuits Maximus ("CMax" for short) is a simple tool that we will use in 6.01 for designing and testing circuits before constructing them from physical hardware. CMax is coded in Python and makes use of the Tkinter and matplotlib Python modules, as well as lib601.

1.2  Installation

CMax is distributed as part of 6.01's lib601 software package. Instructions for installing lib601 can be found on "Infrastructure" page of the course web site at http://mit.edu/6.01.

1.3  Running CMax

On Athena, run the following commands from a terminal:
> add -f 6.01
> CMax

On UNIX-based systems, run the following command from a terminal:
> CMax

On Windows, click the CMax shortcut in the Start Menu (it is located under "All Programs" in Windows 7).

CMax consists of two main components, the circuit editor and the circuit simulator (described in sections 2 and 3, respectively).

2  Circuit Editor

CMax's main window consists of a row of buttons and a virtual protoboard, as shown in Figure 1.
cmax_editor.png
Figure 1: A screenshot showing the 3 components of the circuit editor: the virtual protoboard (1), the prototype resistor (2), and the element toolbar (3).

2.1  Adding Circuit Elements

Circuit elements can be placed on the virtual protoboard by clicking the associated buttons in the toolbar (3). In order, the elements which can be added to the board are: short resistor, long resistor, op-amp, potentiometer, motor connector, robot connector, head connector, power supply, and voltage probe.
Clicking on an element button while holding Shift will create an instance of that element in a different orientation from what is shown. Resistors created in this manner will be rotated 90 degrees, and any other element created in this manner will be rotated 180 degrees.
Newly-created elements appear in the left-hand corner of the board, and can then be dragged to their desired location. Note that CMax allows elements to be placed in locations on the board where there are no holes; be careful not to leave any elements disconnected. CMax does not, however, allow duplicate elements to be placed on top of one another.

2.1.1  Resistors

When a new resistor is added to the protoboard, its value is determined by the value of the prototype resistor (2). There are two ways to change the value of the prototype resistor, both of which will immediately be reflected in the prototype resistor's button:
  1. Clicking on one of the colored bands of the prototype resistor will change that band, cycling through all possible colors. Clicking a band while Shift is held will cycle the colors in reverse order.
  2. Clicking on the prototype resistor while holding Ctrl will open up a new window, into which a resistance value in ohms can be typed; acceptable inputs include "150000", "150K," and "150 kilo ohms". Resistors in CMax only allow for 2 digits of precision; more precise resistances entered into this box will be truncated to two digits. If an invalid resistance is entered, the prototype resistor will not change.
To check the value of a resistor in your circuit, (in case you forget what the colored bands mean), just place the cursor over the resistor.

2.1.2  Wires

Clicking on an empty spot on the protoboard and dragging to a different location will create a wire connecting those two points. Clicking and dragging one endpoint of a wire will move only that endpoint; clicking and dragging in the middle of a wire will move the entire wire.

2.1.3  Power Supply

A voltage source (either from a power supply element or from a robot connector) is required to successfully run any simulation. Clicking on the power supply button will place power and ground on the lower rails. Clicking on the power supply button with Shift held down will place power and ground on the upper rails.

2.1.4  Voltage Probes

You can use voltage probes to measure voltages on the virtual protoboard, just like using a multimeter to measure voltages in a physical circuit. Clicking on the voltage probe button will place + and - probes on the lower rails. Clicking on the voltage probe button with Shift held down will place + and - probes on the upper rails.

2.2  Modifying a Circuit

Elements can be edited once they are placed on the board in a number of ways:

2.2.1  Moving Large Segments of a Circuit

To move a large segment of a circuit, create two (invalid) wires running north-south, extending from above the top rail to below the bottom rail. Then, use the left and right arrow keys to slide everything in between those wires left or right.

2.3  File Management

CMax allows for saving (Ctrl-s) and loading (Ctrl-o) of circuit files. Please use filenames with a .cmax extension when saving and loading circuit files.

3  Circuit Simulator

Selecting Sim → Run Simulation from the menu (keyboard shortcut Ctrl-i) will run a simulation on your circuit, and one or more new windows containing the simulator's output will appear. Some circuit elements (such as potentiometers) require inputs; these inputs are specified via a simulation file, which is a Python script that creates these inputs. You can load a simulation file by selecting Sim → Load Sim File from the menu (keyboard shortcut Ctrl-Shift-i); the currently-loaded simulation file is shown in the status bar at the bottom of the window. You will never need to write your own simulation files; we will always provide them.
In order to get meaningful output from the simulator, your circuit must contain some means of measuring voltages in the circuit; this usually manifests itself as a voltage probe in the circuit. The voltage difference between any two points can be measured by placing a + probe at one point and a - probe at the other.
If the circuit contains an element whose input or output changes over time (e.g. a potentiometer or motor), the simulator will also pop up one or more windows containing graphs of these elements' behaviors over time. If the circuit contains a potentiometer, the simulator will produce one plot of the potentiometer's position (α) over time, and another of the probe voltage over time. If there is a motor in your circuit, the simulator will produce a plot of the motor's speed (in radians per second) and position (in radians) over time.
To close all currently-open simulation windows (plots and text output), use menu option Sim → Close Sim Windows (keyboard shortcut Ctrl-w).

4  Keyboard Shortcuts Reference

New File Ctrl-n
Open File Ctrl-o
Save File Ctrl-s
Save File As Ctrl-Shift-s
Reload File From Disk Ctrl-r
Undo Ctrl-z
Redo Ctrl-y
Run Simulation Ctrl-i
Load Sim File Ctrl-Shift-i
Close All Simulation Windows Ctrl-w
View Documentation Ctrl-d
Quit Ctrl-q

5  Changelog

This section summarizes changes to CMax (arranged by version number1) and tries to let you know who to contact if something goes wrong.

version F14-6

version F13-2

version S13-9

version S13-8

version S13-1

version F12-4

version F12-3

version F12-2

version F12-1

version 1.7

version 1.6

Footnotes:

1Changes were not logged before version 1.6

File translated from TEX by TTHgold, version 4.00.
On 6 Oct 2015, 13:18.