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Author Topic: Low cost homebrew red LED light source for cyan tracks Frank Jerkic Film Handler Posts: 77 From: Ayr Queensland Australia Registered: May 2004 posted 05-28-2005 08:02 AM                        Sorry Bruce I jumped the gun not reading it correctly or completely, as soon as I saw the first few lines well......at least I was not the only one to get confused lol Regards  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 05-28-2005 12:26 PM                     Now, I can understand you people in OZ having a problem. Being on the other side of the equator, you have to read everything up-side-down. I've tried this, and it isn't easy. Besides, winter is right around the corner, down there, and I'm sure that you are all consuming plenty of to keep you warm.  |  IP: Logged Alan Gouger Jedi Master Film Handler Posts: 501 From: Bradenton, FL, USA Registered: Jul 2000 posted 05-28-2005 06:44 PM                        Would there be any advantage using a modified red laser pointer verses a red LED?  |  IP: Logged Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 05-29-2005 07:16 AM                     I don't think a laser pointer will have the output needed compared to a Lumiled. Lumileds are $10 or less and with the proper dropping resistor will run off an existing exciter suppy.  |  IP: Logged Bill Enos Film God Posts: 2081 From: Richmond, Virginia, USA Registered: Apr 2000 posted 05-29-2005 08:17 AM                     We tried using the works from a red laser pointer----like trying to use a 60 watt lightbulb in the lamp housing. Our home mades built according to Jeffs plan are still performing well, they were installed last December.  |  IP: Logged Mitchel Monger Film Handler Posts: 6 From: Sagle, Idaho, USA Registered: May 2004 posted 08-09-2005 07:52 PM                     Hi, Due to the budget constraints of our art-house theater we haven't upgraded to read cyan yet. I just found out that our film that runs day after tomorrow is cyan. I've ordered and received 2 Luxeon Star LEDs. Here are their specs: Part # LXHL-MD1D Max Current - 350ma (300ma or under may be preferable) Max Voltage - 3.5vdc (would I want to run at max?) Color - Red Wavelength - 625 NM Light Dispersal - LAMBERTIAN Typical Flux (Lumens) - 44 The incandescent exciter lamps they will be replacing are BXMs, rated at 9v 4a 36w. We run on two Super Simplex projectors with Simplex SH-1012 soundheads. I've checked the voltage going to the exciter, and it is only 7.5dc. The exciter supply is a Kelmar 8604-B, and is variable from 5-10vdc at 5a. I would like to keep it set at 7.5vdc (if possible) so I can swap out the red LEDs with the BXMs. I need to find out what kind of resistor I need. So far I've figured this: I'd like the Luxeon to run at 300mA, and 3.5v. I need to drop the 7.5v supply by 4v. So, according to Mr. Ohm, R=E/I and P=EI, which means that: 4v / .3a = 13.33 ohms 4v * .3a = 1.2 watts And the closest standard resistors are either 10 or 15 ohms at 2 watts. Is that correct? I certainly don't want to blow the Luxeon or run it too hot or too dim. Which would be a better resistor, the 10 or the 15 ohm? I've been to the local Radio Shack, and they don't even have any 2 watt resistors. They have 15 ohm 1/2 watt, 10 ohm 1/2 watt, and 10 ohm 1 watt. What combinations of common resistors can I put together to get the right value? Thank You.  |  IP: Logged Frank Jerkic Film Handler Posts: 77 From: Ayr Queensland Australia Registered: May 2004 posted 08-09-2005 09:34 PM                        Hello Mitchel, I have made my own LED setup with help from from the design of Jeff Stricker and help from Lindsay in WA and Peter in SA, This beaut little LED system has been running trouble free for 2 months now on my Kalee I am using a Luxeon Star III LXHL-LD3C with a SEPIC Switchmode Driver, The driver provides a constant current supply at up to 10 volts from an input supply voltage of 3.6 to 18 volts,SEPIC drivers are useful in that they can step the input voltage up or down to the required output voltage, When used to drive a LED the output voltage will settle at Vf, the LED forward voltage drop (typically 2.9 to 6.8 volts for high power LED's) The total cost of this was $78 AU  |  IP: Logged Bill Enos Film God Posts: 2081 From: Richmond, Virginia, USA Registered: Apr 2000 posted 08-10-2005 12:20 AM                     Another advantage to these things over the over priced store bought is that you can make up extra ones using the white LEDs and install them in the bulb holders to have white light ready to go for the older prints and especially the variable density tracks.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 08-10-2005 07:58 AM                        quote: Bill Enos Another advantage to these things over the over priced store bought is that you can make up extra ones using the white LEDs and install them in the bulb holders to have white light ready to go for the older prints and especially the variable density tracks. Not sure that a "white" LED will have the same cross-modulation optimization characteristics as a tungsten exciter lamp. How much output in the infrared region? Have you actually played old B&W and cyan+magenta+silver tracks using the white LED and found negligible XM distortion? For cyan tracks, the red LED should ideally have a peak output near 660 nanometers: http://www.kodak.com/global/images/en/motion/products/lab/f010_0294ac.gif  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 08-10-2005 01:29 PM                       John, Thanks for pointing out that "white" light is not what you need for old prints. What you need is the infra-red portion of the spectrum.  |  IP: Logged Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 08-10-2005 03:53 PM                     I'm happy to see folks tinkering with this design as a low cost approach to reading cyan tracks. Industry folks: bear in mind that I don't have test film, so I just relied on my "ears" to evaluate performance. This started out as an experiment just to see "what would happen if..." I was so pleased with the results, that I decided to share it on Film-Tech. Mitchel, you would actually need a forward diode curve to know what the diode voltage is going to be at 300 mils. Gosh, you are wanting to run this thing right at the hairy edge ! Be sure its heat sinked! The best (safest) way to find the resistor value you need is experimentally. My gut feel is that 13.3 ohms will be too low. With 7.5 volt supply, I'd start at about 39 ohms and work down from there. (33, 27, 22, 18 ohms, etc.) Be sure to put an milliammeter in the circuit. Since your exciter voltage is variable, you can "fine tune" the final curent after you settle on a resistor value. Forget Radio Shack junk. High power resistors available from Mouser. They sell small quantities...no problem... http://www.mouser.com/ Super driver circuit you have there, Frank! But, I would still consider running this thing at a lower current than 300 mils. BTW, I still need a a few hunks of cyan film for further experiments--- can anyone help me out?  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 08-10-2005 07:03 PM                     When you don't know the resistor value you need, consider using a potentiometer (variable resistor) and then you can fine-tune it in the field. Radio Shack is probably a necessity if he really needs this working A.S.A.P. --jhawk  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 08-10-2005 07:17 PM                     Caution: a pot may not be able to handle the power dissipation in this case.  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 08-10-2005 07:19 PM                  That's not a very good suggestion Jhawk. There is too much room for damaging the LED. Besides you'd need some humongous WW pot at the very least to dissipate all that heat. Better to stick with the meter and the Ohms Law calcs.  |  IP: Logged Frank Jerkic Film Handler Posts: 77 From: Ayr Queensland Australia Registered: May 2004 posted 08-10-2005 08:45 PM                        Thought I would show you what my little LED looks like, I ran this for a month without any heatsink on the back and found it did not appear to run any hotter than the normal bulb, I decided to add the heat sink just to help it stay cool during the hot summer months that are on the way, I have had some tech bloke visit and look at it and rubbish it but I dont care it works very well thankyou lol  |  IP: Logged

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