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A Prototype Optical Tracking System Investigation and Development - page 72 / 170





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Black Spot Hardware

register set. The MT9V023 registers are a super-set of the older sensor’s but are similar. The MT9V023 has two banks of registers and the sensor can be switched rapidly between each bank. Both sensors were used during production of the board.

Data from these sensors are output using a 10 bit parallel bus and also using a serial Low Voltage Differential Signaling (LVDS) bus. The chips provide a Two Wire Interface (TWI)

bus for control of parameters such as software reset, shutter period, automatic gain control, automatic exposure control, and frame size. The sensor can be clocked at a maximum of 27 MHz and as low as 13 MHz to produce images at approximately 30 fps. The data sheet for the MT9V023 claims sensitivity to light of at least 55 dB and at least 100 dB using a compander mode. The chips are designed for a 1/3” optical format allowing for smaller optics than some other chips considered that use a 1/2” format. t the time of selection, the sensors were available in a BG package, however, a similar model (MT9V032 [79]) is now available in a slightly more prototype friendly CLCC package. They are most responsive to light with a wavelength of approximately 600 nm with slightly lower efficiency at the

LED wavelength of 510 nm.

t the time of selection both chips were available from the

merican electronics supplier

Digikey for approximately $30 US with a minimum order quantity of 1 unit. However, at the time of writing Digikey does not stock these parts giving weight to moving to the CLCC packaged part that remains available.

For the prototype, the MT9V023 sensor was used on two of the three prototypes produced. The MT9V022 sensor was placed on the other prototype board.


Design considerations

During the design of the camera module, parameters such as size, power requirements, cost, and interference issues were considered. The modules will be attached to the head of a laser scanner, therefore, they must be small and light so that the scanner does not become unwieldy to use. Since this design is a prototype the requirement of producing a small design can be relaxed, however, it is important that the design is compact enough such that the prototype can be developed and reduced in size in the future.

Each module must consume little power to minimise the heat produced. Since there will be many modules in the system the overall power consumption will be many times greater than the power consumption of a single module. nother design goal is to keep the part count low primarily to reduce the production cost and make routing the PCB easier. The ease with which the PCB can be routed is also affected by the high speed signals in the

design, i.e., the fewer high speed buses there are, the easier it is to route.

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