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This section discusses a simple way to create your own board designs without a CAD (Computer Aided Design) program. If you are using printer-ready board layouts, such as those in the Daqarta Circuits folder, you can skip this section.
The best way to create your own board layouts is definitely by using a CAD program, even if you will be using the felt-tip direct-draw method. There are many CAD programs available, including some good free ones such as ExpressPCB that are intended for use when ordering commercial boards from that company.
But if you are using the direct-draw method you can quickly create a simple layout using graph paper. This can be nearly as fast (and sometimes faster) than using a CAD system.
You should lay out the design on 0.10 inch grid tracing paper (frosted mylar is better) as though you were viewing the circuit from the top (component side) of the board, looking through it with your X-ray vision to see the copper conductors or "traces" on the bottom side.
Use a normal black pencil for the bottom conductors and red for the top-mounted components. Mark a black dot where each hole will be.
Don't agonize over getting the "perfect" layout: You may need to use one or more plain wire jumpers where you can't easily avoid the need for two conductor traces to cross.
Be sure to consider how the finished board will be mounted, and mark mounting holes as well... typically one at each corner.
Standard Dual Inline Package (DIP) integrated circuit (IC) chips have 0.10 inch spacing between pins and 0.30 inch between rows. The parts are shipped with a slightly greater row spacing and must be bent to fit the 0.30 inch spacing when installed.
Don't try to run traces closer than 0.10 inch center-to-center. That will allow the lines to be drawn later with a standard felt-tip marker and still leave reasonable spacing between them. Commercial boards can use narrower spacing, and even run "sneak-through" traces between the pins of a chip, but that would be very difficult with the hand-drawn method.
Allow at least 0.40 inch between the holes for each standard 1/4 watt resistor if you want it to lay flat in the normal manner. Alternatively, though not recommended, you can choose to stand these on end for much closer spacing, at the cost of greater height of the finished circuit.
Frosted mylar has a big advantage over tracing paper for layout, since you can erase and redraw repeatedly as you experiment with different arrangements. Look for this at a major art supply store, especially one that caters to a university clientele. If you can't find it with a 0.10 inch grid, you can always tape plain frosted mylar over graph paper which will show through while you draw.
If you are only going to make one small circuit, it's probably not worth a big quest to get this stuff... thin graph paper will work just fine, or even thick graph paper if you have (or can rig up) a simple light box to view the final result from the back.
A CAD program can keep track of conductors and components on separate "planes" of the drawing, and can print out normal or reversed views on standard paper. CAD makes it much simpler to rearrange things as you work out your design. Just make sure that you can get the printed dimensions correct on the final printer output, or the pins of the IC chips won't fit!
See also Printed Circuit Construction
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