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The schematic for this entire project is available as a PDF file suitable for printing.  Download PDF schematic (98k).  The schematic was generated using CadSoft Eagle layout editor.

The power supply for this unit is a simple linear supply regulated to 5V.  The transformer I used was actually a unit salvaged from a wall-wart power supply, providing 9VAC at about 400 mA.  The AC voltage is passed through bridge rectifier B1 and filtered by C1.  A National Semiconductor LM2490 was chosen as a regulator for its high efficiency and low dropout voltage, but a standard LM7805 could be used just as easily.  C2 provides filtering post-regulation.  All components were chosen for low price and small size (the case I used was only 2" x 4" x 1.5").  If you build this from this design, be sure not to omit the proper switching and fusing components.

Datasheet: LM2940

Copyright © 2004 Michael Shevlin
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