Adventures with Spatial Light Modulators15 December 2005Breakthrough paper: Applied Optics 28, 22, 4845 (1989). 14 December 2005I tried shorting pins PL1 and PL2 on the Sharp LCDP, as suggested by Chuck Pancake. Sadly, this did nothing - the red "LAMP" message is still the only thing that appears when the unit is turned on. All is not lost, though, as we saw Frank Chin of instructional labs at the physics department holiday party and he said that he probably has an extra bulb for the Sharp projector! Yay! When I first saw the Sharp QA-1650 LC device, my jaw dropped in awe. It is a 16 cm by 22 cm LCD. That's right, 352 square centimeters of liquid crystal glory. It requires a conventional overhead projector, so it doesn't have all the bulb-related complications. Its logo-screensaver is amazingly vibrant! I plugged it into the WINXP and immediately I saw the computer's output. The colors aren't as wonderful, though, and the entire screen does not show up on the LCD. I tried the WIN95 machine also; the colors were brighter, but still the resolutions did not match. I must investigate the differences between the WIN95 and WINXP video output, and look for a manual for the Sharp 1650. I think I should name each projector something like "Steve" or "Benny" so I don't have to get all dyslexic with the model numbers! 13 December 2005Dr. Noé and I went to talk to Chuck Pancake in the electronics shop. Fooling the ballast unit may be as easy as shorting some pins. Yay! 09 December 2005We've obtained more LCDP's (and a new couch!) from the university's property control. There are four Proxima DP 2810, a Sharp QA-1650, and a Proxima DP 6150. I got the Proxima 2810 to work with a WIN95 machine but not WINXP. It requres 640 x 480 resolution and 72 Hz monitor refresh rate, which the WINXP should be capable of providing. I think there's a general problem with the ShuttleX's graphics drivers anyway. 02 December 2005We plugged in the Sharp LCDP and learned that the $300 metal halide lamp is dead. We don't need the bulb as we want only to use the LCD elements. Tricking the electronics into thinking that the bulb is still there is more complicated than replacing it with a large resistor. The lamp has negative resistance, and therefore requires additional electronics (the ballast unit) to prevent the lamp from killing itself. Metal halide lamps are related to mercury vapor lamps, but use halogens and other metals (most offen NaI or ScI) in addition to mercury. The lamp requires an arc discharge to create a sufficient amount of iozided mercury for full operation. This is accomplished via a high voltage pulse or an additional starting electrode (as in pure Hg vapor lamps). The ballast limits the amount of current supplied to the lamp, and is often used to control the starting also. Apparently its function is related to aspects of a switched-mode power supply. 02 December 2005I found a MS thesis by Pierre Lane (then of the Technical University of Nova Scotia) about the transformation and characterization of a Kodak LCDP to an SLM for use as a Fourier-transform coprocessor. It has an excellent review of LCs and SLMs, details characteration experiements we could do with our own Sharp LCD screens, and has many very nice references. Dr. Noé and I had a long discussion on various video imputs. The Sharp LCDP has three input options: composite video (yellow coaxial), S-Video (4-pin mini-DIN), analog RGB analog (15-D-sub in two rows). Analog video is a composite signal that contains the luminance (Y) and chrominance (U and V) information. The signal is a complicated mountain-looking waveform, half of which contains steps that encode 256 colors. There are many encodings of analog video, including NTSC (in the USA and others) and PAL (in Europe). NTSC uses interlaced scanlines at 60 Hz, which creates a flicker-less picture, and prevents "rolling bars" by matching the CRT electron beam scanning with the AC line voltage. (Such "rolling bars" can be seen when you videotape a computer monitor.) PAL uses 50 Hz to match the European 50 Hz AC signal; a flickering picture is more likely to be observed. S-Video is a component signal, where luminance (Y) and chrominance (C) signals are unmixed. RGB has seperate red, green and blue components (and also often a sync signal) and is used in computer monitors. My house recieves about five television channels. These are picked up by the antenna as amplitude-modulated RF signals. The envelope of the high-frequency RF becomes the video signal, which is sent to the CRT. The Sharp's LCD is transmissive, twisted-nematic, electrically addressed, and driven by thin film transistor. Each LCD panel has 455 vertical and 497 horizontal elements. There are only 16 wires going into the LCD panel, though, so something exciting is happening in there that the manual does not describe! 16 November 2005We obtained a Sharp XG-2000U 1993 LC projector from the wonderful
people in instructional labs. I ordered the service manual on eBay (I
love the Internet). Jay, Dr. Noé and I discussed how to proceed,
which includes figuring out how reflective SLMs work, contacting the
physicsists from the University of Regensburg that we met in Tucson,
and looking for papers discribing the transformation of a LCDP to an
SLM. We also explored a LC clock.
Azure Hansen, Stony Brook University, 2005
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