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A Prototype Optical Tracking System Investigation and Development - page 84 / 170





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Black Spot Hardware

Ltd.) was used and they placed and soldered these parts. To do this, firstly, the solder paste stencil was used to place the solder onto the BG pads on the PCB. The BG parts were then machine placed. To allow this to be done, fiducial markers were added to the PCB in the design phase. This enables the machine vision system to automatically place the parts

in their correct locations.

The panel containing the three loaded boards was placed in a

vapor phase oven that heated the solder until the BG

parts were fixed to the board.

The remaining parts were placed by hand at

SL. The resistors and capacitors were chosen

specifically to be large enough to solder by hand and are 1.6 mm x 0.8 mm (0603) parts.


the boards were tested it became apparent that modifications were required. These usually involved cutting tracks and rewiring parts. Modifications are listed in Section 5.5.1.


PCB modifications

Throughout the development process modifications were made to the original schematic to

fix errors in the design. There schematic changes lead to PCB modifications.

n overview

of these modifications are described here with detailed diagrams in

ppendix D.

Buck converter modification

The original schematic contained an error that caused a short between the 5 V power rail and ground. This was due to an error in the buck converter circuit. The board did not function at all before this modification.

Flash select line

The Blackfin requires the flash select line to be connected to processor flag PF2. Initially this was connected to a different processor flag. This resulted in the board not being able to load program code from the flash.

Image data bus modification

Initially the eight least significant bits of image data were connected to the lower eight bits of the PPI port and the two most significant bits were connected to bits 8 and 9 of the PPI port. While this is not a problem if 16 bit reads are used on the Blackfin it does become a problem if 8 bit reads are used. During development it was decided that 8 bits of image

data were sufficient for processing.

better scheme then is to route the 8 most significant

bits into the lower bits of the PPI port allowing them to be read in 8 bit read mode. modification was made to do this.

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