Designing Your Own Device: Getting Started with AutoCAD

The following gives some useful guidelines for using AutoCAD to create your own microfluidic designs. AutoCAD is a comprehensive software package, but for purposes of getting started quickly only a select number of instructions are given here, which can be used in creating 2D designs for microfluidic circuits. These guidelines are meant for those who have never used or are only vaguely familiar with AutoCAD.

Have fun designing your microfluidic circuit!!


1.0 Getting Started

Working in AutoCAD can be done using command line instructions, point-and-click commands, menu selections, or a combination of all three. Functions are often duplicated between each style of working - many command line instructions can be found in the menus, etc.

1.1 Layers

To create objects/shapes in AutoCAD start by selecting an appropriate layer to draw it in. The pull-down layer menu is most likely found in the top right of the AutoCAD window and lists the layer name, color, if the layer is active/displayed (light bulb is on), and if the layer is locked or not (if it is locked you are not able to modify this layer). To create a new layer or modify an existing one, go to Format->Layer. When designing the microfluidic circuit, a separate layer should be used for each resist layer in your design, i.e. control, flow_rounded, flow_nonrounded, etc. There are 3 other pull-down menus related to the main layer menu found to the left on the screen. The 'ByLayer' option should be selected in these 3 menus so that the correct attributes for each layer are represented in the drawing window.

1.2 Units and Precision

Before you start your design, ensure that the internal units and precision is set up properly. Go to Format -> Units and make sure the Precision is set to 0 and Scale/Units is set to 'microns'.

1.3 Creating Shapes

Once you have defined and selected the appropriate layer, you can start to draw your design. One way to do this is to choose the desired shapes from the panel menu on the left of the screen, i.e. circles, lines, rectangles, polygons, etc. After clicking on the desired shape and clicking in the drawing window to initiate the shape, you can either simply terminate the shape by clicking in the drawing window or use the command line to specify quantitative details for the shape. For example, a circle can be drawn by clicking on the circle in the panel, clicking in the drawing window to define its midpoint, and then typing the desired radius in the command line.

1.4 Miscellaneous

When working in AutoCAD, be sure the 'Model' tab is selected on the bottom part of the drawing window. When saving an AutoCAD file, save it as a .dwg or .dxf format.

 


2.0 Drawing Tools

2.1 Measuring Objects

To measure the length or area of a shape you simply use the ruler tool located as a point-and-click option on the top left of the window. You may also use the menu option to access this tool Tools->Inquiry->Distance or Tools->Inquiry->Area. If you want to measure length, activate this tool and click the length you want to measure in the drawing window. If you want to measure area, activate the area tool and click on the vertices of the shape you are measuring, press enter to get the final area result.

2.2 Changing Layers of Shapes

If you want to change the layer of an existing shape, simply select the shape and go to the main layer pull-down menu and click the desired layer. The shape layer will change immediately. Keep in mind that if the chosen layer is not active (light bulb is off) these shapes will not be displayed in the drawing window until you activate this layer by turning on the light bulb (clicking on the bulb).

2.3 Helpful Options

Some helpful options are located at the bottom of the drawing window including the ORTHO and OSNAP options. The ORTHO option allows you to draw straight lines or move shapes in a straight line easily and snaps to the closes 90 degrees. The OSNAP option enables you to accurately select vertices on shapes and lines, making it easier to align and join objects at specific locations, etc. Once OSNAP is active and you select a shape to draw, dragging the curser across existing shapes reveals specific vertices (indicated by yellow squares) and midpoints (indicated by yellow triangles) clearly.

2.4 Creating Text

It is very useful to label your microfluidic circuit with information such as project number, version number, date, etc. Instead of drawing shapes to create individual letters, a Lisp script has been created which allows you to generate letters via the command line in AutoCAD. First, in an internet browser go to http://thebigone.stanford.edu/foundry/maskdesignrules.htm and click on the 'linetext' hyperlink to download the Lisp script as well as a linetext-readme.txt file of how to use the script. Save these files in an appropriate directory. To create text in your AutoCAD design go to Tools->AutoList->Load and browse your directories until you find the saved Lisp file. Then click 'Load' and close the window. In the AutoCAD command line enter '(linetext)'. The program will first ask you to enter a location for the text; click in the drawing window where you want to initiate text. Then enter the text you would like to write in the command line. Press enter and the text will appear in the desired location. The text will be quite small so you will need to zoom in to see it and also scale it up to an appropriate size.

Note: before using the linetext program, ensure that the ORTHO and OSNAP options at the bottom of the drawing window are deactivated, otherwise the text created will be distorted.

 


3.0 Manipulating Objects

3.1 Moving

To move a shape in the drawing window, select the shape by clicking on it or drawing a select box around it using the left mouse button. Then right click and choose 'Move'. Click on the shape and move it to the desired location. You can also specify the number of microns you would like to move it by initiating the move in the desired direction (having the ORTHO option active at this time is recommended) and then typing the number of microns in the command line.

3.2 Mirroring

To mirror a shape, select the shape and then choose the point-and-click mirror button or use the menus Modify->Mirror. The command line will ask you to specify the first point of the mirror line. Click to define the mirror line (it is recommended to have the ORTHO option active at this time). Then the command line will ask if you want to delete the source object. If you simply want to mirror the existing shape type 'Y', but if you want to produce a copy of the existing shape type 'N'.

3.3 Rotating

To rotate a shape, select the shape and then choose the point-and-click rotate button or right click and choose Rotate. The command line will ask you to specify the base point or rotation point – click on the shape to indicate this point (it is recommended to have OSNAP active at this time to quickly be able to select specific vertices). Then type the desired angle of rotation in the command line.

3.4 Scaling

To scale the size of a shape, select the shape, then right click and select scale. The command line will ask you to specify the base point from which scaling should occur. Click on the desired base point (it is recommended to have OSNAP active at this time to quickly be able to select specific vertices). Then type the desired scaling factor, i.e. if you want to increase the size of the shape by 1% type 1.01, if you want to decrease the size of the shape by 10% type 0.90.

3.5 Arraying

Many times it is useful to copy a specific shape a number of times with predefined equal spacing between each copy. This can be done in one axis (X or Y) to create an array or in both axes to create a matrix. Select the desired shape and go to Modify->Array and choose the number of rows and column you would like to produce of this shape. Select if you want a rectangular or polar array (rectangular array most common). Indicate the desired row and column offset (remember to add the width and length of the shape if you do not want the shapes to overlap). Note that a positive row offset adds rows upwards and a positive column offset adds columns to the right (specifying negative offset numbers adds rows and columns in the opposite directions). Specify the angle of the array in degrees (for a conventional rectangular array this would be zero).

3.6 Unionizing

Shapes can be unionized to become one single shape. When drawing in AutoCAD, shapes and lines will be composed of 'polylines' or 'lines'. To verify this you can find the properties of a particular shape by selecting it, right clicking, and selecting properties. Once you are satisfied with your shape, you are able to join or subtract it with/from another shape. However, to do this you must change the shape property to 'region' by typing 'region' in the command line, clicking on your shape, and pressing enter. Verify this change by checking the shape property again. To join two or more shapes together, ensure they are all regions. Then type 'union' in the command line, click on the desired shapes, then press enter. The shapes should now be joined to form a single region. Before unionizing, make sure that the shapes are overlapping or clearly joined by their vertices to avoid unwanted, almost undetectable gaps between shapes.

3.7 Subtracting

Subtracting shapes from each other can be useful to create custom shapes. The procedure is very similar to unionizing shapes. First, the specific shapes must be regions (see Section Unionizing to learn how to do this). Then type 'subtract' in the command line, enter, select shape 1, enter, select shape 2, enter. This sequence results in shape 1 – shape 2 = shape 3.

3.8 Object Properties

To know the properties of a specific shape, click the shape, then right click and select properties. In the properties window you are able to change shape properties such as layer, line type, line weight, the coordinates of specific vertices, the length of a line, etc.

3.9 Zooming

To zoom on the drawing window, simply use your middle mouse scroll button to zoom in or out. You may also use the point-and-click zoom in and zoom out buttons on the window panel.