User's Manual

PointBlank Product Specification, Rev A

4.1.1 PointBlank FPGA

The PointBlank FPGA receives LVDS image data from the DDP ASIC. Under control of the

software and sequences in the DDP ASIC, it inserts the PointBlank patterns into the normal

image data and outputs it to the DMD.

The LVDS inputs in the FPGA do not have internal termination resistors so external parallel

termination must be added on the PCB. TI recommends using filled vias for these signals at the

FPGA so the termination resistors can be placed across the vias.

The FPGA is a LFE2-12E-5FN256CB9 made by Lattice Semiconductor. Firmware and an I/O

spec for the part are available on the PointBlank Knowledge Base. Further information on the

FPGA is available on the Lattice Semiconductor website.

The FPGA requires 3.3V, 2.5V and 1.2V. The 3.3V is powered directly from the 3.3V from the

PMD1000. The 2.5V and 1.2V should be generated with linear regulators from the 3.3V. See the

reference design for details.

4.1.2 PointBlank Radio Transceiver (PBM)

The TI reference design uses an eZ430-RF2500 2.4GHz radio transceiver development board.

This board’s main components are a TI CC2500 2.4GHz transceiver and a TI MSP430F2274.

Documentation for this board and its components is available on the TI website (www.ti.com).

Additional information on antenna selection is also available.

The DDP ASIC communicates with the radio board with a SSP (SPI) bus 1. The MSP430 is the

master and the DDP ASIC is the slave. The DDP ASIC can request data from the MSP430 by

asserting a GPIO pin (request to send). See the DDP2230 PointBlank reference design

schematic for details on the connections between the DDP2230 and the eZ430-RF2500 board.

4.1.3 PointBlank Pointing Device (PBP II)

The PointBlank pointing device utilizes a photodiode to sense the amount of light in the projected

image. Optics in the pointing device reduces the field of view of the photodiode so the pointing

device sees a relatively small portion of the screen from a typical user distance. TI uses a 36mm

lens with a 2mm aperture located at the focal length of the lens just in front of the photodiode.

For a 75in diagonal XGA image and the pointing device located 55 in from the screen the spot

size has a horizontal diameter of about 3.7in or 62 pixels. It is important to minimize any light

reflections inside the optics housing as these can degrade performance at the edges of the

screen.

Current from the photodiode is converted to a voltage with a trans-impedance amplifier. The

output of the trans-impedance amplifier is high passed filtered to reject DC and 120Hz ambient

light sources. After filtering the signal is gained up with a programmable gain amplifier. The

output is then sampled with an ADC in a MSP430. The measurements are sent to the projector

over a 2.4GHz wireless link. The pointing device utilizes a TI CC2500 radio transceiver to

transmit messages and receive configuration. See the reference design for more details on the

pointing device electronics.

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