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Small to fit inside the PC in the place of the CD-ROM.
To reduce the size of the PCB there is two tricks in
the design
1- There is no base resistors for the driving transistors.
instead the pins connected to the transistors bases is
defined as input pins and the pull-up resistor is used
as a base resistor
2- In the schematic the collectors of the sink transistors
are connected to the ground but when the board is
assembled the collector and the emitter is reversed
so the emitter grounded
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