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Author Topic: Low cost homebrew red LED light source for cyan tracks John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 10-24-2004 12:09 AM                        quote: Jeff Stricker I did notice that the focus setting needed to be "tweeked" when going from tungsten to red LED. I'm not suprised since I doubt the slit lens has any special coating to correct for chromatic aberation (I think that's the term for different wavelengths focusing slightly differently??). If anything, the slit lens should have an easier time precisely focusing the relatively monochromatic light from a red LED. With a tungsten lamp, chromatic aberration adversely affects the ability to focus across the visible and infrared spectrum.  |  IP: Logged Bill Enos Film God Posts: 2081 From: Richmond, Virginia, USA Registered: Apr 2000 posted 12-01-2004 06:50 PM                     Today we finally did the install on the homemade red LEDs. No difficulties were encountered. We had to slightly adjust the focus of the lens, adjusted the output level of the preamps and did a general routine going over of everything else. The tick on change over is no more than with exciter bulbs. Plays black and cyan tracks equally well. The only unanticipated thing is a very low level 120hz hum from the Smart exciter supply, a filter cap. will fix that tomorrow. A back-up LED assy. is in the drawer in the event of a failure, as is an exciter lamp which will work with just a reduction in the level control.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 12-01-2004 08:27 PM                       As a rule of thumb, you need to get the ripple down under .5 mVolt P to P before it is inaudible in a normal theatre  |  IP: Logged Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 12-02-2004 05:59 AM                     Glad these are working out. With ample filtering, you will have zero hum...Jeff  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 12-02-2004 06:33 PM                     If possible put the cap on the LED side of the resistor. (In other words, across the LED). A swiching type power supply may get rid of the problem as well.  |  IP: Logged Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 12-08-2004 04:39 AM                        Hi all I have completed a commercial install at a country cinema useing low cost leds.In a pair of aussie Raycophone machines,that use rear scanning heads. The outcome is out standing,[no extra pre amps to muckup the sound either] there was a small drop in vol from ex lamps,nothing the smart 230 couldnt handle with head room to spare. The low cost fix for good quality sound. I have a bench mounted sound head to carry out such testing,with a selection of sound optics to play with,you learn alot just by playing around with odds and ends. Stan Gunn  |  IP: Logged Oscar Neundorfer Master Film Handler Posts: 275 From: Senoia, GA Registered: May 2000 posted 12-08-2004 08:29 PM                        Stan, You actually still have a SMART 230? That product was long obsolete when I came to work for SMART over 21 years ago. I had 2 of these in my museum until a few years ago when someone who shall remain nameless decided to "get rid of all the junk laying around". Being the packrat that I am, I was highly agitated with this person.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 12-09-2004 08:07 AM                     quote: Stan Gunn The outcome is out standing No offence Oscar but I don't see with that processor how Stan could hear if the results were "out standing" or not. I'm shocked that there are any of thise still around . Mark  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 12-09-2004 09:45 AM                     I sold a bunch of them to independent operators.... simple puppies for the time and market conditions.  |  IP: Logged Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 12-09-2004 09:54 AM                        Yes Oscar There are still 230s AND 130s in use,I service 2 sets in small country multi use halls,They serve the purpose that they were made for, to provide sound in the place the people sit to watch the pictures. The sound is good considering the hall acoustics. The 230 developed a sever hum, traced to the power transformer one plugpack and a bridge rectifier later quiet as a mouse. I also have a collection of smart units. Mark. When I am outstanding in the hall it sounds ok. Stan Gunn  |  IP: Logged Peter Mork Expert Film Handler Posts: 181 From: Newton, MA, USA Registered: Jun 2002 posted 12-10-2004 03:30 AM                     I put one of my homebrew lights in a different RCA head - it didn't light. Then I noticed the power to the head had been wired backwards, plus for minus. This was no problem for the incandescent bulbs, but even when I fixed the polarity, the homebrew was dead. Question - will a short reverse shot of 12v DC kill an LED that easily?  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 12-10-2004 05:56 PM                     No, putting 12V backwards across an LED should not harm it. Get out your VOM and check for voltage across the LED, and check for the proper polarity. If you are going to be trying the LED in different sound heads, you might want to put a bridge rect. before the LED. Connect the + and - to the LED, and feed power into the ~ (AC) leads. The bridge must be able to handle the current that the LED draws, and the voltage as well (this should not be a problem).  |  IP: Logged Clive Carmock Film Handler Posts: 24 From: Morden, Surrey, UK Registered: Dec 2004 posted 01-02-2005 11:20 AM                     Having just discovered this post I have already ordered the parts I need to try this myself. I have a Zeiss TK35 projector, which uses a mirror to bounce the beam from the exciter through 90 degrees. My concern is slit uniformity. The TK35 has a small ground glass 'screen' to help with adjustment of the exciter. In operation an image of the filament appears on this ground glass screen. The exciter is then adjusted to bring the image inline with a black line etched onto the glass. It will be interesting to see what happens with a red LED. However given the small cost of the components it has to be worth a try. For those in the UK wanting to do this I found that Maplin Electronics stock the LEDs mentioned here (www.maplin.co.uk). Regards Clive  |  IP: Logged German Marin Expert Film Handler Posts: 227 From: Verbania (VB), Italy Registered: Jul 2001 posted 01-05-2005 05:01 AM                     What would be the standard luminous intensity for a red LED? There's LED's working between 300 mcd and 8,000 mcd... it's a big difference! Germàn.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 01-05-2005 09:51 AM                     A TK35 owner in Germany are having good results using a laser pointer from an office supply store with good results.  |  IP: Logged

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