CMax Documentation

Circuits Maximus v1.6 Documentation MIT 6.01 Introduction to EECS I Contents 1 Getting Started 1.1 What Is CMax? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Running CMax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 2 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 . . 2.3 File Management . . . . . . . . . . . 3 3 3 4 4 4 4 4 3 Circuit Simulator 3.1 Common Simulation Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5 4 Keyboard Shortcuts Reference 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Getting Started 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 Numpy modules, as well as lib601 (specifically the sm and sig modules). 1.2 Running CMax On UNIX-based systems, navigate to the directory containing CMax.py (inside the week’s distribution) and run the following command: > python2.6 CMax.py On Windows, use Windows Explorer to navigate to the directory containing CMax.py and double-click it. Alternatively, open CMax.py in IDLE and hit F5 to run it. If you open CMax this way, you will need to close IDLE in order to close CMax. Note: Please make sure you are using the proper version of CMax (1.6). Immediately after opening CMax, try hitting ctrl+a, which will show a window with information about CMax. You should see that the CMax you are running is version 1.6; if you do not see a window, or you see a different version number, please make sure you have opened CMax using the instructions above. CMax consists of two main components, the circuit editor and the circuit simulator (described in sections 2 and 3, respectively). 2 2 Circuit Editor CMax’s main window consists of a row of buttons and a virtual protoboard, as shown in Figure 1. 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. 3 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: • To move an element to a different location, click on the element and drag it to its desired location. • To delete an element: either click on the element while holding Ctrl, or drag the element so that it is completely off-screen. • Certain elements (anything but a wire, probe, or voltage source) can be rotated by clicking on the element while holding Shift. • CMax also offers multi-level undo/redo support. The keyboard shortcut for undo is Ctrl-z, and the keyboard shortcut for redo is Ctrl-y. 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. 4 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 po­ tentiometers) 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) over time. 3.1 Common Simulation Error Messages • Failed to solve equations! Check for short circuit or redundant wire This can be caused by connecting power to ground, for example. Examine your wiring. Maybe you inadvertently used the same column of holes for two purposes. At worst, you can systematically remove wires until the problem goes away, and that will tell you what the problem was. • Element [‘Wire’, ‘b47’, ‘b41’] not connected to anything at node b41 The name ‘b41’ stands for the bottom group of five holes, in column 41. If you get a message like this, check to see what that element should have been connected to. You know that there should be something else plugged into the bottom section of column 41, in this case. • Could not solve for voltage at node j42 This usually occurs when you have a probe placed at node j42, but nothing else is connected there (there is no voltage to measure). • Element not in valid holes This means that you have a wire or element that has an end or a pin in position on the board that does not have a hole. 5 4 Keyboard Shortcuts Reference New File Open File Save File Save File As Reload File From Disk Undo Redo Run Simulation Load Sim File Close All Simulation Windows View Documentation Quit 6 Ctrl-n Ctrl-o Ctrl-s Ctrl-Shift-s Ctrl-r Ctrl-z Ctrl-y Ctrl-i Ctrl-Shift-i Ctrl-w Ctrl-d Ctrl-q