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Using the Schematic Entry Tool to Create Circuits

The Elements Panel
The Work Area
Connecting Elements
Editing Elements
Converting to Netlist
Schematic Variants
Device Models

The schematic entry tool (SET) enables you to create circuits graphically, instead of typing netlists. However, before the schematic circuit can be simulated it has to be converted into a netlist, which is then fed to the simulator tool. Since analysis tasks can not yet be specified in the SET you have to manually add them to the netlist after the schematic has been converted.

The Elements Panel

The elements panel contains all circuit elements, which can be copied to the work area. It also includes three control buttons and a slider to adjust the transparency of the panel. Open the elements panel by clicking on the Elements button in the toolbar or by selecting Show Elements from the Window menu.

Circuit elements are organized in groups (e.g., transistors, diodes, power sources). The elements you see in the panel are the current selected elements from their groups. To see all elements of a group simply right-click (or CTRL+click) on the visible element. A popup menu appears and you can choose another element.

The slider at the bottom adjusts the panel's transparency. This could be useful in situations where the panel is positioned in front of the schematic due to limited desktop space.

The Work Area

The work area is where you create your circuit. To add elements to the work area simply drag and drop it from the elements panel. To move circuit elements within the work area either drag them with the mouse or use the arrow keys for more precise positioning. When using the arrow keys you can move faster by additionally pressing the Shift key ().

Unlike most schematic tools MI-SUGAR uses no grid. Instead, there are placement guides to help you align the circuit elements. These guides are vertical and horizontal green lines and appear whenever two connection points align. When moving a selection of multiple elements this feature works only for the one element which is under the mouse pointer.

To select multiple elements either click on the desired elements while pressing the Command key, , or draw a selection box around the elements by clicking on an empty area and dragging from there.

The work area has a limited size. Border lines are drawn in orange. You can navigate within in the work area by panning and zooming: To pan the view click on an empty region of the work area, hold the mouse button pressed for one second, then drag. You can also use the Option key, , in combination with the arrow keys or drag with the middle mouse button if you have a three-button mouse. Yet another way is to click on one of the bars that appear when the mouse pointer comes close to any of the four sides of the schematic view area in the window. To zoom the view use the slider in the tool bar or the plus and minus keys (+ , –). You can also use the scrollwheel of the mouse if you have a mouse with scrollwheel. Note: A three-button mouse with scrollwheel is highly recommended for MI-SUGAR.



As a navigation help, clicking on the Home button in the toolbar moves the view back to the lower left corner of the first quadrant of the work area.

 

Connecting Elements

Circuit elements have connection points which allow them to be connected to other elements. A connection point is highlighted in red when the mouse is on top of it. To connect two elements click on the connection point of the first element and drag the pointer to the connection point of the other element. (If you wait longer than 1 second after clicking on a connection point the mode automatically switches to element dragging. Use this feature to drag very small elements, like node elements, which are covered with connection points.)

After you start dragging, a connection line will be drawn from the connection point to the mouse position as long as you keep the mouse button pressed. The connection line follows a three-point route. The originating connection point and the mouse position are the first and the last points, respectively. The middle point is chosen automatically so that the connection line is split into a horizontal and vertical component.

When the pointer is on top of an unconnected connection point the connection line will turn red. Release the mouse button to make the connection. A connection point can only connect to one other connection point. If the target point is already connected new connections will be refused. Use node elements (in the elements panel) to connect multiple points with each other.

To disconnect two elements drag the connecting line at one of its two connection points and release over an empty region.

Tip: When you drop a node element on a connection line, the node will be inserted at that point.

Editing Elements

The Info panel allows you to inspect schematic elements and edit their properties. Open it by clicking on the Info button in the toolbar or by selecting Show Info from the Window menu.

All elements have a fixed type name and an editable label and can be annotated with a comment. The info panel shows these properties at the top, next to the buttons, which let you rotate and flip elements and set the relative position of their labels.

The area below these common fields depends on the type of the inspected element. For subcircuits the namespace, the revision and the pin-to-node assignment matrix are shown. For ordinary circuit elements a table with editable device parameters is shown. A resistor, for example, has the single parameter resistance while more complex devices, like diodes and transistors, have more parameters. Parameters can be edited by double-clicking on its value field and typing a new value. Values for the model parameter are selected from a list (see Device Models).

Tip: To create an exact copy of an element press the Option key () and drag it with the mouse. Use this feature to quickly generate a bunch of elements with the same orientation, the same label, the same label position and the same parameters. To copy elements from one window to another use C for copying the selected elements and V for pasting. Note that the elements will be pasted to the same positions they were copied from and that connection lines are not copied.

For elements with a single parameter the value can be viewed directly in the schematic by pressing the space bar. Pressing the space bar again hides the values.


Converting to Netlist (Capturing)

Clicking on the Capture button in the toolbar will convert the schematic into a netlist, which replaces the previous content of the netlist editor. The conversion process assigns node numbers to all connection points of each circuit element. The same number is assigned to all electrically equivalent points. Zero is assigned to all points connected to ground, and -1 is assigned to unconnected points.

Control commands (.op, .ac, .tran, .dc, etc.) of an existing netlist will be lumped together and placed right after the title line of the new netlist. This allows you to quickly repeat an analysis task after making modifications in the schematic.

After capturing the schematic you can view the assigned node numbers directly on the schematic. Press the space bar to make the node numbers visible. Press the space bar again to hide the node numbers.

Note: For now, the produced netlist is compatible with SPICE only.

Schematic Variants

For each circuit you can have up to four schematics. Only one of them can be active at a time. Although these four schematics can be totally independent of each other the idea behind having more than one schematic is to manage a set of similar schematics. That's why they are referred to as variants. Variants are especially useful when you have one main schematic of a circuit and want to experiment with modified versions, which require only minimal changes to the netlist after capturing.

The four dots in the tool bar of the circuit window represent the available schematic variants. The current active variant is indicated with a red dot. The keys 1, 2, 3 and 4 are used to switch from one variant to another. By pressing 1, 2, 3 or 4 you replace a variant with a copy of the current variant.

Device Models

Device models are used to describe the electrical behavior of circuit elements. Some models are more accurate than others or more suitable for a specific analysis task. SPICE lets you specify the device model of a circuit element and its parameter values in the netlist. But you don't need to because MI-SUGAR supports device model assignment in the schematic: Elements with selectable models have the Model parameter and it can be set in the info panel by selecting a model from the popup list.

You can manage your personal model repository in the Device Models window. To open the device models window select Show Device Models in the Window main menu. You will see a list of device model names on the left side and the parameter values of the selected model on the right. The content on the right is freely editable and will be inserted into the netlist during schematic capture. This means that you can use comment lines if you want to. Please note that the keyword .model, the name of the model and the opening and closing parantheses must not be included in the parameter list and each new line must start with a plus (+) symbol.

To create new device models make copies of one or more existing models by selecting their names in the list and clicking on the Copy toolbar item. Double-click on each copied item to change its name. To delete device models: Select their names from the list and click on the delete button in the toolbar. For each category of devices a default device model is included. These default models can not be deleted or renamed.

Selected device models can be exported to a file by clicking on Export, and then choosing/setting a target file name. Other users can import those exported device models by clicking on Import and selecting the previously created device models file. The device model collection used by MI-SUGAR is stored in the file Device Models in the folder Application Support (in the folder Library in your home directory). It is read from during startup and saved to when quitting.

When a schematic has elements that use non-default device models the device models are included in the saved file and will be added automatically to other user's device model libraries when they open the file.