Realizacion De Circuitos Impresos

EXPRESS PCB TUTORIAL
Revised 1/11/2010

This tutorial leads you through the design of a PCB using layout software from ExpressPCB, which is freeware available at www.expresspcb.com. Before beginning you should make sure your computer has both ExpressPCB and ExpressSCH, if not than you should download the software. Before beginning the PCB process, you should come up with the initialdesign, build it and test it on a breadboard, fix any errors, and determine specific components. It is also useful to have datasheets and dimensions for all of the “special” components such as transistors, ICs, sensors, actuators, etc., on hand. For this tutorial, we will use a drawer burglar alarm circuit, which had the following form after testing on a breadboard:
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There are twostages remaining in the process to creating the circuit board. In the first stage, you build the schematic using the ExpressPCB schematic editor. In the second stage you layout the circuit board. It is possible to skip directly to the layout editor. However, doing the schematic first will allow you to link the schematic into the layout editor reducing the probability of error.

Entering theSchematic into ExpressSCH

1. Open ExpressSCH to create a fresh schematic. The first time you start ExpressSCH you will get a dialog box with a link to a quick start guide for ExpressSCH. This can be useful if you want to get a general overview for the tool. Once you are ready to start, close the dialog box to view the empty schematic.
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2. Click on Op-Amp-like symbol to placecomponents. To place the resistors, select “Passive-Resistor” in the text box in the upper right corner.
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3. Then click on the schematic for the 4 resistors (not including the photoresistor or potentiometer) in roughly the location you want them to display. Then zoom in using the magnifying glass tool (or the wheel on the mouse) and pan the display (using the sliding bars) to improveyour view.
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4. Now you need to give each of the resistors unique identifiers. Right click on a resistor and choose “Set component properties.” In the Component Properties box, under “Component ID,” select “Auto assign Part ID.” The program should assign this resistor to be R1. Set its value 10k in the “Part Name” field and hit OK. Repeat this process to identify and label R2(10k), R3 (100k), and R4 (10k).
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5. Rotate R4 by right clicking on it, selecting “Rotate component” and then “Body left 90º”
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6. Now add the capacitor, potentiometer, comparator, and transistor to the circuit by first clicking back on the component placement tool (the red op-amp symbol) and using the component names “Passive-Capacitor polarized,” “Passive- Potentiometer,”“IC – National - LM311 – Comparator – DIP-8,” and “Semiconductor – Transistor NPN.” Use “set component properties” to assign all of these parts Part IDs, label them and position them (using the arrow tool) in a logical manner.
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7. Now we need to add some components (the photoresistor and the buzzer) that don’t exist in the library. Let’s start with the photoresistor. The easiest wayto make new parts is to start with a symbol that’s already close to what you want and modify it. Place a regular resistor on the layout (using the placement tool with ‘Passive – Resistor’). Go to the selection tool (the arrow), choose that resistor and go to the “Component” menu at the top and select “Ungroup component”
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8. Using the circle shaped tool from the tool menu, draw acircle around the resistor.
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9. Select the whole object (using the arrow tool), and choose “Component” -> “Group to make component”
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10. In the component properties box that appears, assign the photoresistor a unique part ID, such as “PR1”.
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11. For future use, save this as a custom component by selecting “Component” -> “Save custom component” and then in the...