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

Saturday, August 13, 2011

Crazy Analog Memory

Sadly i recently had to dismember my ancient Tektronics Analog scope, it happened to be manufactured in 1967 and was the first analog storage scope commercially available from Tektronics

Channel one was toast and the tube was quite slow but it did its job for a year after i pulled it from a dumpster along with a few hundred pounds of industrial equipment.

It will be missed, although it has been replaced with a much faster and considerably smaller analog scope and a function generator. I stripped it for parts and scrap aluminum simply because i am moving in a few weeks and could not find a home for it. Lots of dials, switches, tubes, germanium diodes and whatnot inside but there was something that made absolutely no sense, a heavily shielded cable about 2 meters long stuffed inside of a shielded box labeled danger high voltage. It has 2 enameled wires inside tightly wound around a plastic core, i worked out that each wire had to be several kilometers long.

After some pondering i concluded that this had to be what was used for the storage component of the scope. It simply used the length of the cable to provide sufficient delay followed by amplifying the signal and feeding it back into the other end, an analog version of delay line memory.

Friday, August 12, 2011

POV Clock

I found an interesting persistence of vision clock for a few dollars at a local thrift shop

Its a simple 8 led array on a thin piece of pcb held up by a spring with a magnet, a large coil pulls the array forward and the spring does the rest of the work, the base is a nice polished piece of aluminum... when running there is a surprising amount of rocking force so a heavy base makes sense


Other than showing the time there are a number of annoying messages, looks to be an easy thing to hack

It is controlled by an old Atmel AT87F52 microcontroller, an LM339 comparator for the break beam sensor (i think), 74hct244 to drive the leds and a 2k eeprom to store custom messages. A ksp2907 transistor drives the coil. I would like to replace the mcu with something more modern, with a proper RTC and communication, adding RSS feed capabilities and maybe changing the led color