La ACES Student Ballooning Course
Electronics Unit
Activity E8. CAD Tools for Circuit Design
Summary:
Students will learn to use ExpressSch to draw schematic diagrams, and ExpressPCB to lay out an
etched circuit board. A simple adjustable-voltage power supply will be the design example.
Materials:
This activity is best performed either individually or in pairs. If desired, an informal
"competition" might be organized, with the goal of the smallest physical size of the final design.
Each person or pair should have available the following materials, equipment, and supplies:
1. Pencil and paper and calculator
2. Printed copy of the data sheets reference below.
The laboratory should also be equipped with the following:
1. Flat work tables sufficient to seat all students with plenty of work space
2. Computer(s) (PC) with ExpressPCB (included on LaACES CD-ROM) software installed
Procedure:
1. Design an adjustable power supply based upon the LM-317 voltage regulator integrated
circuit. A data sheet for that device will be found in the References folder of the Electronics
unit on the LaACES CD-ROM. Example circuit implementations will be found on that data
sheet. A suggested block diagram is below:
In
n
diode
protection
LM317
regulator
potentiometer
adjust
Out
n
The input voltage will be from a 12 volt battery pack, and the output voltage should be
variable from less than 1 volt to greater than 9 volts. The power supply should include a
potentiometer to serve as the voltage adjustment control, diode protection from reverse
polarity (see SkeeterSat for an example), as well as connections for input and output voltages,
and ground. A fuse for short circuit protection would also be a good idea. A data sheet
showing the physical size of an appropriate potentiometer is also included in the References
folder.
2. Use ExpressSCH to draw a complete schematic diagram of the circuit. Be sure that every
component has an ID label and a value. It may be necessary to create a custom symbol if a
part is selected that is not in the library of standard components.
3. Use ExpressPCB to link to the schematic diagram and create an etched circuit board
pattern for the power supply. It will probably be necessary to create a custom component for
the potentiometer. Try to make the board as small as reasonably feasible.
4. Use the ExpressPCB cost estimating feature to determine the per-board cost for orders of
5, 25, and 100 boards.
LSU v06/04/2007
Electronics Unit - Activity 8
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La ACES Student Ballooning Course
Electronics Unit
Activity E8. CAD Tools for Circuit Design
Expected Outcomes:
A minimum implementation of the design should be a circuit including a rectifier diode,
LM317 regulator chip, two capacitors, a fixed resistor, a variable resistor, and optionally, a
fuse, and perhaps LED indicator. It is likely that a circuit board pattern not more than about 5
cm square will be large enough to hold all the components
Issues:
In order to discover all of the tools needed to complete this activity students will have to
spend some time reading through the extensive Help files within both ExpressSCH and
ExpressPCB.
References:
ExpressPCB software installation. filename: <ExpressPCBSetup.exe>
LM317 Data Sheet. filename: <LM317 Data Sheet.pdf>
Potentiometer Data Sheet. filename: <Trimmer potentiometer data sheet.pdf>
LSU v06/04/2007
Electronics Unit - Activity 8
2 of 2