Keeping an old 8mm projector alive with high-power LEDs

There’s a certain mystique about old home movies and 8mm film; whether it’s footage from a family gathering from 40 years ago or a stop-motion animation you made when you were 12, there’s an immediacy for film that the VHS tapes from your family’s first camcorder can’t match. [Teslas Moustache] has been getting into 8mm cameras and projectors, so when he came across a 8mm/super 8 projector that needed a bulb, he knew he had a worthwhile project on his hands.

To replace the burnt-out and very expensive to replace incandescent bulb, [Teslas] sourced a very bright star LED from Jameco. This 1 Watt LED puts out more than enough light to project a frame of film onto a screen and fortunately doesn’t get as hot as the stock bulb.

To power the LED, [Teslas] used a cell phone charger powered from the 120 VAC incandescent socket to supply the requisite 5 Volts at 1 Amp (Ohm’s Law works on coffee) power for the LED. Right now, there’s still the matter of fabricating a nice enclosure to mount the LED and charger in the bulb socket, but once [Teslas] figures that out, he’ll have a very nice 8mm projector on his hands.

Comments

  1. Dax says:

    I don’t think a 1 Watt LED is nearly bright enough for the job, seeing that the original reflector bulb was a 150 watt incandecent. Getting a similiar amount of light from LEDs would require about 30 Watts worth of them.

    Granted, we could slash that down by quite a lot since we don’t know how much of the bulb’s light actually ended up in the optics, but it’s still going to be in the 10 Watt range.

    • DanJ says:

      I agree Dax, but that LED is being operated at > 1 W. The LED is connected directly to the power supply. A 1 W LED is usually specified for 350 mA operation at Vf (~3.2 volts). His PSU can probably put out more than 350 mA into a low impedance, perhaps as much as an amp. Even with great heat sinking/cooling, he’s probably shortening the life of the LED significantly.

    • DanJ says:

      Fun idea though. I like the idea of restoring old technology like this.

    • Dax says:

      A more sensible option would be to replace the original socket with a socket for halogen capsule bulbs, and use a 100 Watt halogen bulb instead. They can be found for couple dollars a pop.

    • Dave says:

      You’d be surprised how little of the energy from the incandescent bulb actually ends up as light squeezing through the tiny 8mm gate. These little LEDs are easily bright enough, if you drive them at their peak pulse current rating, and make sure all of the light goes through the hole.

      • Dax says:

        I know how tiny the gate is, but you’re still comparing a LED that gives out 70-80 lumens, and a lamp that puts out well over 2000 lumens.

        You have to assume that over 95% of the light is lost if you want to argue that the 1 Watt LED is effectively as bright as the original lamp.

      • Dax says:

        Correction, a 150 W ordinary bulb will output 2600-2800 lumens, because high powered incandecent bulbs are more efficient. If it was a halogen bulb, you’d get nearly 4000 lumens out of it.

        The 1 Watt LED is simply dwarfed.

      • Dave says:

        All I’m saying is “don’t knock it till you’ve tried it” I know I was surprised!

  2. Pat says:

    “1 Watt LED … to supply the requisite 5 Volts at 1 Amp”
    Did I read that right?

  3. Blaise Pascal says:

    A 1W LED requires a 5V supply at 1A? How does that work?

  4. Dave says:

    I did a very similar thing recently. I had a projector that was quite cheap, and didn’t have any means for stopping the light while the film was moving across the frame. I replaced the bulb with a 2W LED, and was very pleased to note that the light just covered the film gate (which is very small with 8mm, of course!), making for a very efficient projector. I mounted it with hot glue to meccano, and bolted it into the case where the bulb mount used to be.

    Next up, I added an infra-red light gate and a cardboard disc to the rear of the projector, on the drive shaft. I noticed that the shaft turned 360 degrees once per frame, and about 2/3 of the travel was during the “dwell” time, in which the film was stationary. So, I cut out a part of the disc corresponding to the part of the cycle where the film was moving, and mounted the light-gate such that the disc passed through the middle of it.

    Now I had an electronic switch that turned on and off in sync with the film’s motion, so I just knocked up a MOSFET driver to the LED and wired in a 5V DC power supply for the whole thing. A bit of hot-melt later, and I had a huge improvement on the picture quality of the original projector, with the added bonus of a much cooler lamp (so no chance of melting film if it gets stuck!)…

    I should document it all one day…

  5. DanJ says:

    Probably Dax, but where is it written that hacks need to be “sensible” – whatever that means? A hack can be a way for the hacker to explore something they’re interested in. It makes sense someone would be interested in replace an incandescent light bulb with a LED.

  6. John says:

    The LED here really should be driven with a constant-current driver. As DanJ mentioned above, the LED used here is probably rated for 350 mA, and driving it at a current much higher than that is a sure way to greatly shorten the life of the LED. By simply using a cell phone charger directly to power the device, you have no way of knowing how much current is actually being supplied.

    If you simply search for “constant current LED driver” or “driving high power LEDs”, there are plenty of schematics, kits, and commercial drivers designed to do this, most of which would not add significantly to the cost of the project. I would highly recommend driving the LED at constant current at the specifications provided by the manufacturer (slightly overdriven would probably be fine too, but not to the extent it is currently being overdriven) to avoid prematurely destroying it. Great project though, awesome way to resurrect and improve older equipment!

  7. Eddie says:

    If I remember correctly, 8mm projector bulbs have a parabolic mirror in the bulb, behind the filament, to maximize the light going to the gate.

    Maybe a halogen bulb is better in this application?

  8. PI says:

    What do you guys think of this idea…

    1.) Disable the projector’s mechanical shutter so that the optical path is always open.

    2.) Install an optocoupler to the shutter drive so that the optocoupler is triggered every time the shutter would have been open.

    3.) Use the the optocoupler to drive a high power LED.

    Since the LED is now being run in pulsed mode with a short duty cycle, it should be possible to up the drive current significantly without damage to the LED. This gets you more light from the LED.

    • tyco says:

      When you pulse power into an LED to get an average power consumption, you indeed get more light, but only in situations where you are running at less than 100% of the rated capacity of the LED. It turns out that constant-current-100% and pulse-mode-overcurrent-to-average-100% provide about the same light output.

      In this case you’d get a bit more brightness solely because you stop losing the light that would be blocked by the camera’s shutter. But that’s unique to this particular situation.

      Also, photon flux does not scale with current after you exceed the maximum rating of the LED. Not far beyond the maximum rating, diminishing returns kicks in, and more current does not result in more photons. At that point, you simply must have more semiconductor to perform the electron-photon conversion, there is currently no way around it.

  9. conundrum says:

    @Pi, good idea!
    These LEDs can certainly tolerate pulsed current of at least three times their max mA rating at room temperature, there will be some loss of efficiency over time as the diode degrades but this shouldn’t be too bad.
    A temperature feedback that backs off the current as the LED begins to heat up should take care of thermal runaway..

    The limiting factor in many of these is actually the bond wires, same as C*s*o laser diodes.
    Maybe plate over these to increase the thickness and then use a white phosphor sheet made from a few drops of EL phosphor dried onto a sheet of glass.

  10. Galane says:

    I’m waiting for someone to hack together an LED replacement for digital LCD projector bulbs. I have a nice 1024×768 Toshiba from 1999. $10,000 new – $10 used = 99% discount. :) The bulb in it still works, no idea for how long it’ll stay working. $150 for a new bulb rated for 2,000 hours.

    First thing on projectors for light source hacking is disabling the startup bulb test and high voltage output. Hooking up a massive resistor to dump it into is not at all practical but has been done in short tests.

  11. whizbo says:

    I think that carpet is as old as the projector. :)

    Cool Project!!

  12. conundrum says:

    I also have one of those projectors. Maybe someone should start a “Hack your cheapass 3 colour LCD projector into 3 nice colour ones” using RGB LED panels.
    Come to think of it, RGBY ought to be quite feasible for the same cost.
    Save on costs by switching the same constant current driver between multiple LEDs and drive the panel at slightly elevated temperature to take advantage of the higher switching speed.

  13. DivePeak says:

    Overcurrent will destroy the LED, but the original bulbs had a pretty short life to start with and cost a lot more, so who cares?

    The original design put out a hell of a lot of heat, and a hell of a lot of light didn’t go through the gate. Still won’t be enough light to operate at the original distance/screen size, but the inverse square law could make it usable at a smaller size.

  14. Robot says:

    What is being missed in this conversation is the need for a nearly coherent and uniform illumination field if a quality projection is desired. Regardless of the light source by necessity one will need to throw away a lot of light in hopes of producing a uniform illumination field. While a high powered LED with integrated optics can be used to project an image there will be notable artifacts due to the LED die and uneven output across the die. This can be addressed with micro-array optics comprising many small lenses which integrates many smaller illumination fields into a larger illumination field. Alternatively, an array of LEDs could be used where each has it’s own primary optic; the output of the array would be integrated with a secondary optic and focused onto the “gate” and finally projected with the projection lens.

    Hopefully I didn’t confuse light with lite to (or too) many times.

    – Robot

    • Carl says:

      We can all agree that, the advantage of using a LED vs. the original bulb, is the operating temperature is substantially cooler than that of a bulb and therefore, won’t burn film that could become stuck in the gate. The other, of course, would be the availability of a replacement bulb.
      The concerns over the LED’s inability to produce enough light to project an image, shouldn’t be an issue for those of use that will only be projecting the image into a transfer box. I believe the amount of lumens required for that application would be substantially less than projecting an image onto a screen several feet away. Making the LED a viable option.

  15. drrickdaglessmd says:

    I’m thinking of attempting a similar hack on a Bell & Howell Autoloader 357B super8 projector I have laying around.

    Essentially, this model is more or less in working order and is a pretty clean example, but unfortunately it lacks speed control (18/24 fps). I’ve been a fan of super8 films for a while and this isn’t my main projector, so I’m thinking it’s ripe for a hack (I have a mix of 24 and 18fps films in my collection).

    I’m thinking of using a high-power LED like the one in the article to replace the 150w projection lamp, replacing the drive motor with something in better condition (after 46 years, it seems the motor isn’t firing on all cylinders and struggles a bit when winding 400′ reels), adding a speed selector/tuning knob, all tied together with a microcontroller for PWM, etc…

    After reading some of these responses I was curious about the optocoupler design idea, but when I took a look inside there’s no easy way to decouple the worm gear shaft from the shutter mechanism (that drives the winding sprockets for the film feed mechanism).

    Anyway, it’s great to see I’m not the only one who thinks about fixing up old super8 projectors.

  16. deskgrommets says:

    1 Watt?? Will it give enough light for the projector to be used??

  17. mike says:

    What is the status on this project?
    I used a gu10 2 w 110v bulb on an 8mm projector but it was too dim.

  18. Isobel Proc says:

    I have the exact same projector and the lamp went out on it recently…Could you make me one?

  19. hAR. says:

    one of my current projects is very simular to this one, although would like to replace the lamp of an old slide projector with an LED, and afther that building myself small slide-like-projectors to use in my installations.

    but like i said, i’m an artist, not an engeneer and my intrest in all these technical stuff is rather fresh, so yes i’m rather new to all this.

    is there a possibility that there is somebody out here able to talk me true this kind of project in more detail (that may be a lot more detail) with the right information (according to use a ccd, heatsink, the right kind of LED, the right power supply etc.). or to recommend other pages/fora/books…. where i might find the information i need as a beginner.

    thank you all in advance!

    Your comment is awaiting moderation.

  20. Leon Whitman says:

    I need a replacement for a Bell and Howell 8 mm projector that calls for a DAR bulb which is 500 watt with a reflector in the rear. After a few hours in the chamber (I think it is SM3190, the bulb gets pregnant and can’t be removed from the chamber except by crushing it and that is messy. This is an old B&H 8mm Design 122 Model G. The specs call for a bulb not over 500 watts (DAR) but it runs so hot (even with the fan running continuously) the air coming out of it will burn your hand. I need something that puts out about 200 watts or an LED replacement. Any suggestions? Leon

  21. Jac says:

    I bought a 30 watt, 6000 degree K, 2500 lumen LED that is 7/8″ by 7/8″ along with a 30-36 volt DC transformer. found an old 2″ by 3″ heat sink and mounted that with ONE screw where the old bulb used to be. Plenty of room. Took out the old bulb and its base by removing the back with 6 screws. can then connect the power supply input to the two leads and voila…. it works great. Used velcro to mound the small linear power supply on the top of the projector. the Projector Fan cools the LED just fine and it never got above 100 degrees which is below its rating of 130 degrees F. Am converting like mad with NO burned out bulbs and not burned film on a jam… which happens now and then….

  22. Al says:

    Gonna be trying this–with a 35mm projector soon….
    –The idea above to run a pulsed-lamp for film projection isnt new. Philips did exactly that in the early ’60’s for FP-20S pulse-lamp 35mm cinema projectors. The lamps were small–about the size of a Xenon flash-bulb in a still camera, held in a water-chamber constantly supplied with cold water, with a tiny mirror, there was a quartz window on the other side. Two lamps were used per projector, one active and the other spare/standby. When the first failed, the second was automatically put into service–a turret arrangement of the water-chamber turning into position–allegedly in the blink of an eye so hardly noticed. Each lamp was rated at 800W and life was allegedly 30 hours per bulb.
    Although only 800W, due to the small size of the optics used, less light was lost. like in the usual 2000W Xenon XBO types.

    A pulse-generator on the intermittent-movement flywheel synchronised the bulb on-time, which was driven by a large thyratron rectifier box, full of valves, about the size of a spin-dryer.
    Bulb pulsed three times per 24th second picture.

    I propose summit similar using a 150W LED mounted close to the film gate driven by optocoupler arrangement as described above. The ‘Kinoton’ projector I’m getting is basically a Philips machine, even has the cut-outs the original design has on the int. movement flywheel….

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 92,308 other followers