Saturday, October 18, 2014

Telecine Projector: Hardware Details

Quite a few years ago I did a digitization project for a number of 8mm reel to reel home movies. The setup was pretty simple: an old brownie projector, a large screen and a Hi-8 camera. The result was adequate for the time, but required quite a bit post processing to clean up. Film can run at 16 to 18 ish frames a second while the camera ran at 24 static. The color was off, everything was either too dim or over exposed. Additionally when a frame is advanced it is blocked off momentarily to prevent blur during pull-down, this is made more periodic to make it less noticeable to the human eye but causes serious issues with video cameras recording at a faster rate. At the time it took me 6 months to process mpeg-2 video, having to clean up frames one by one at times. This was around 2005 and my phone now is several times more powerful than my computer was then, the results were pretty good considering the resources at hand.

Sometime afterwards I acquired an old 8/Super 8 projector and decided to take another crack at this, having squired 50 or so more reels that needed digitizing. The first step was to gut the entire projector of its electrical, fabricate a new takeup reel and make modifications to the film gate.

Gutting the projector was the easy part, other than the lamp housing and the transformer there was little else in this thing.

Regarding the film gate, a sizeable portion of the film is not seen on the projection. The image is cropped down so the perforations are not visible along with the intermediate region between frames. Since i want to capture as much of the film as possible I enlarged the gate as much as possible for both Super-8 and Regular-8 Film

The original take up reel was missing so I ended up adapting one from an old reel to reel magnetic tape player, it fits and the wobbly thing on the end that allows the reel to hold tension in one direction while allowing the projector to go in reverse works.

I decided fairly early on to use an arduino for the brains of the projector. There isn't much requirements wise: control the brightness of the bulb, advance to the next frame, load film so i picked a fairly cheap easy to program Arduino and a motor control shield and called it a day.

The lamp was a bit of a tight fit, i needed sufficient material to act as a heat sink while allowing for enough room for a reflector without it touching the claw down mechanism. I used a 5300K CREE X-RE led module in a small drop in module cut down to size bolted onto a 1/4 inch thick piece of aluminium that i managed to cut down and make fit.

In order to drive the LED properly I threw together a simple NPN sink drive circuit with a 10 ohm 2 watt resistor in series. Generally driving a power LED with a resistor for current limiting is a bad idea but in this case the load is so small the chance of overheating and the resistor allowing too much current is not a concern.

In order to advance by a single frame I needed a way of knowing when the claw mechanism finished pulling down the next frame, fortunately them main drive pulley controls this directly via a notch on the side that pushes down a little spring arm. So using a black mark on the drive wheel and a photo reflective sensor this is easily achieved.

The original switch control has a position for threading the film that moves some channels to get the film to bend in the right shape. Back when I did this I was lazy and didn't probe out the original switch so I ended up mounting a mechanical switch where I could detect the mechanical position instead.

For the purpose of threading I installed a photo interrupt switch to detect the leader, since its more or less useless for detecting the film itself since it barely absorbs infrared light. 

Most of the hardware modifications ended up being straightforward however the camera took quite a bit time to get right. I ended up choosing a logitech c600 webcam for the imaging sensor, at the time it was the highest resolution 4:3 webcam available for end users. It took longer to find appropriate lenses that had a short enough focal point while being adjustable. I ended up going with a surplus machine vision 22mm lens that screwed into a brass bushing. The dimensions were perfect for it so slide into the mount that held the original projection lens. I glued the webcams lens mount to some scrap plastic that allowed the sensor to be centred in the bushing. The lens had a gear machined into it i ground off to make it fit flush to the projector.

I added a small heatsink to the lcd to try and keep it cool in an attempt to keep it cooler to reduce noise. No clue if it will help but doesn't hurt. The power supply is just an old atx psu i wired up for 12v and 3.3v power nothing special.

Tuesday, October 7, 2014

Hand Gattling Cannon Thingie

After some finagling with parts to make a good fit I managed to finish at least one of these, most of the work was building a cable harness connecting the switch, battery pack and the motor. The rest was finding acceptable materials for a friction drive for the motor.

It works reasonably well for a random prop idea cobbled together from scrap aluminium from a hard drive, curtain rods and a wine chiller.

Saturday, February 23, 2013

Light Table

Simply because i wanted to clear up some space currently being taken up by spare parts i built a light table. Basically its the front bezel and backlight from an old monitor, a ccfl driver and 12 power supply, a sheet of glass and a leg from an old portable barbecue.


Scrap Aluminum Challenge

While cleaning and sorting through my heap of things i noticed things bits and pieces that fit together. All of a sudden i found myself building a pair of Gatling style hand cannon props out of bits of scrap aluminum, hard drive platters and spindles.

I still have to cut the barrels to length and drill out the holes, had to order in a 16mm drill bit to match the diameter of the barrels. Also i will be trying to get the motors to run, i have my doubts the low torque motors would be able to turn with the added weight but i don't see a problem in trying.

Thursday, January 5, 2012

Projector Control Circuit Details

 I have received several requests for schematics and source code for the control system i built for my projector. After several months of delays and procrastinating here they are:
 The circuit is relatively straightforward, the relay is sunk by an npn transistor... there is a protection diode to prevent any unfortunate kickback. The reset pin on the micro controller is puled up with a 1k resistor and there is a 0.01 uF capacitor to filter power. The micro controller listens for a control signal and a feedback signal is given by pulling it to ground using an npn transistor.

The code is extremely simple, the mcu waits for the control signal to be high for more than 250ms then enables the feedback signal and turns on the relay until the control signal goes low. The entire thing is in an infinite loop.

#include <htc.h>
#define _XTAL_FREQ 4000000


void main()
    TRISIO = 0b111010;
    ANSEL = 0;
    CMCON = 7;
        GPIO = 0b000000;
        // wait for power on signal
        for(int x = 0; x < 250; x++)
            if(GPIO1 == 0) x = 0;
        GPIO = 0b000101;
        // wait for power off signal


Friday, October 7, 2011

LED Projector Mark II

After completing my first led projector mod i was commissioned to do another one, with an even more powerful led this time

This time around i modified a phillips hopper sv10, which had a burned out polarizer i replaced earlier in the year. Thinking the interface would be identical because of the same manufacturer and they were similar models built around the wrong time, obviously i was wrong.

Instead of a heart beat signal and active low feedback the control signal was a simple active high pulse, feedback required a constant 5 volt line to be pulled down. Using my scope wasn't very helpful as i was expecting a squarewave signal (really need a second probe while im at it) but my new logic probe made quick sense of it.

This time around i used a 50 watt led, 32 - 36 volt power supply, reflector and a pack of credit card frenel lenses to play with.

I mounted the led exactly the same way as before: i removed the uhp bulb cage and hacked off a piece that screwed onto the rest of the assembly

Drilled small pilot holes for mounting the led

Then drilled and tapped for 6 - 32 screws

The plastic piece i hacked off was bolted to the top to mount the led at the perfect position.

 A bit of thermal silicone to hold the led in place and give better thermal conductivity

And finally screw into place. My control board is nearly identical to my previous version, with the exception of the extra transistor used to pull the 5 volt line to ground

Alot smaller and cleaner than my last version, also i found a place to pull 5 volts off the power supply removing the need for its own supply.

Im still in the process of testing different lenses but the credit card frenel lenses seem to do the trick... im a bit concerned that it might sag during prololged operation since it is just a piece of cheap plastic.
Time will tell i suppose, perhaps adding a fan to blow over the front of the led is a solution.

So far it is quite a bit brighter than the 25 watt led i previously used, but it does get much hotter and i will need to attach a fan directly to the heatsink i used, seems to get close to 45c right now but that is with the case open

I am unable to take proper pictures of the projector in action, everything i take with it is way to dim to make out most of the projected image

Nearing the completion of the project i had an accident: i dropped a screw while reassembling the projector which just had to hit a 400v 150uf capacitor which discharged onto the control interface cable and destroyed it... The projector survived, could turn on and off and would display fine through vga but i could not change any settings or inputs making the projector quite useless.

I guess its off ward to the next one, an eiko EIP-2500 DLP projector... i plan on taking the led system from the now failed mod and installing it into the dlp projector

Tuesday, August 30, 2011

Camper Trailer LED Conversion

My parents recently got a camper, which was a huge step up from a tent and considerably better than the cramped tent trailer from my childhood. One issue for myself was the lighting, almost all campers still use 12 volt incandescent bulbs, they bathe everything in a terrible orange glow and either are too dim or have a pathetic lamp life of less than 200 hours.

This simply would not do, my parents did not use the campers lights simply because the damn lights got too hot and melted the polycarbonate dome causing it to sag. They used too high a wattage bulbs but the ones that were rated for the fixture you could not even read by.

A quick bit of searching and i found appropriately sized cool white 108 lumen 12 volt led panels, they took forever to arrive but a a price of 2 dollars apiece on a bulk order in november i would not expect them to arrive any time soon anyways.

Considering the life expectancy of leds drops quite a bit at higher temperatures and that the panel would be enclosed i decided to add a heatsink. Mounting the lights ended up being easier, i simply broke the the glass and soldered the panel directly onto the wire that held the filament. The result was alot sturdier than i thought it would be and required no modification to the fixture. The heatsink was attached using some silicone thermal glue.

The result was impressive, the light given off was much better than the original bulbs. A much better brighter white light. The leds get around 35c after being left on for an hour... considering that they will not be under continuous use and will only be used seasonally i would expect them to last the life of the camper.

A few of the led panels exhibit problems when they heat up