Laser projector

[remp]

Hi there. Thanks for the offer Fiat1. I have two motors both from old printers. One has 6 mirror facets and is crystal controlled to run at 7701 rpm at 24 vdc but it will run slower if I lower the dc voltage. The other is rated at 10500 rpm has 8 mirror facets and needs a squarewave to run it. If I give it 500 Hz it runs at 500 rpm. If I give it 6000 Hz it runs at 6000 rpm. Very handy sort of circuit you have there Fiat1. Send me an email if you like. Some of you may be wondering why I am playing around with a silly little mechanical system which turns out a raster so dim you can hardly see it. Several reasons. Its a prototye system to see if it works. Potentially better definition than a LCD. I know modern LCD are extremely good but can you get modern ones. Adjustable format by altering the polygon speed. Dont need a projection lens.
Cheap to play with. All I am using so far cost me $20 or so. The way I look at it is I have to get a visible steady raster on my projection screen first. Even if the screen is only 4 feet away and the raster is 1 foot wide it is a start. Its good mental exercise every day while cutting the grass or something I am thinking how to do it without spending big money. Also lots of things I dont know how they work so I have to look it up on the internet.
At the moment I am thinking about interlacing. I can do it with a piezoelectric deflector. Just shift the main source beam a small amount each field. Or an electrostatic small movement mirror. Doesn't need to be fast. A small mirror on a loudspeaker might work. The reason I have to think about this is using the projector as a large tv the tv station sends lines 1 3 5 etc up to line 312 and a half. Then it sends lines 2 4 6 8 etc. I could buy a computer board to store the lines and output then in the correct sequence. Have to see how much they are.

[Fiat1]

What is your email adress and how to I change my email address on this forum?

[remp]

If you click my profile button Fiat1 it will show you about me and there is a line there to send me an email. I am sorry I do not know how you can change your email address. Perhaps someone can help you or you could contact the administrator. I am still thinking about the interlace problem. A computer card to do the job will cost me NZ$550-NZ$750 defending on the features, and since I dont need one for any other reason I will leave that. Best plan at the moment seems to be to draw both fields of a frame on top of each other because they are identical. That helps a lot because instead of drawing 625 lines from top to bottom I just need to draw 312.5 lines from top to bottom then start at the top again. I will be away for a few days helping to decorate the hall for the volunteer firebrigade annual dance.

[pa]

I'm on an Sony 1271 Crt projector 50 Hz with a 3.2 x 2.50 (1.33)interlaced mode, if you are under 5 meters near the screen you can see the big lines... The interest of a scaler is to make an interpolation beetween line 1 and line 3, because the line 2 and 4 are on a next image, so if i'm right you can't just reorder the sequence of lines.
There is several interpolartion modes explain in
deinterlace.sourceforge.net/downloads.htm
There is no problem to see TV with a scaler, you just need a video input board.
I think there is some questions :
Do you want to use DVD with more lines ?
compatibility 16/9 and 3/4 Ratio ?
Composite, RVB, or SDI inputs ?
Vertical and Horizontal Frequencies ?
Vertical and Horizontal Synchro mode ?
Remote control ?
I still think a PC will help, doing all this tasks...
e.g 50 Hz 516 lines interlaced input -> 75 Hz progressive 700 lines output.
Or we can buy a Faroudjia ;-)
Pa

[remp]

Hi back again. We had a very succesful dance. Raised some money for the volunteer firebrigade. 10 dollars for a dance per person with a live band, good supper and terrific atmosphere hard to beat. Today I planned on seeing some raster lines. Using the 8 facet horizontal polygon would have required a revolving device to separate the 8 lines coming from the polygon otherwise I would just see 8 lines on top of each other. To avoid using a vertical polygon I used an alternative. By mounting a small mirror 1/2 inch x 3/4 inch on top of the horizontal polygon I could arrange some mirrors on a radius around the polygon and by tilting each mirror slightly I could get lines. Bought a thin mirror from the $2 shop and a glass cutter. Cut the mirror into rectangles 2 inch x 1 inch. Cut some wood pieces inch and 3/4 wide x inch and a half long x 1/2 an inch thick. 1/4 inch in from one end cut a slot with my table saw 1/4 inch deep. At the other end drilled a hole to take a number 8 pk screw. Mounted each mirror in the saw cut on each piece of wood using folded paper to make a tight fit. Arranged a wooden surface level with the single mirror on top of the polygon and arranged the mirrors in a radius centered on the polygon motor shaft. Switched on the 5 mw laser diode which you remember is now modulated with horizontal sync pulses and did some lining up of the mirrors. End result was 8 horizontal raster lines with various spacings between lines. By adjusting the pk screw in the mirror mounts I could adjust the mirrors to give about a 1/16 inch spacing between lines. I was very pleased with the result. The sync pulses had to be lined up vertically by moving the mirrors but I got an 8 line raster. There were a couple of problems. I could not cut the glass exactly so some lines were longer than others. The mirror was only revolving at 1500 rpm should have been 3000 rpm (50 fields per second x 60 seconds=3000 rpm) I ran it slower for safety reasons. Will have to improve the mirror mount otherwise it might fly off. By running at 1500 rpm instead of 3000 rpm I got 2 sync pulses per raster line. Should be only one. Will be only one at 3000 rpm.
There was an unexpected bonus. With one raster line it was quite dim. 8 raster lines was quite a bit brighter as each raster line contributed to the impression of brightness. That will not happen to the same extent when I apply video modulation to the laser diode. Correction. In my post above I said the A and B fields of a frame are identical. They are not identical, they are very similar.
Next step is to secure the mirror on top of the polygon so I can go up to 3000 rpm. Put a 10 turn pot in my signal generator so it becomes easier to make the sync pulses stand still and maybe cut some more accurate mirrors.

[remp]

Put a second 10 turn potentiometer in my signal generator driving the polygon mirror and it works good. Now have a 10 turn 10k coarse speed adjust and a 10 turn 2k fine speed adjust. Plenty of control. Can make the sync pulses stand still for long periods of time even though the generator is not very flash. Secured the single sided mirror on top of the polygon and increased motor speed to 3000 rpm. Got one sync pulse per line. Tried to cut more accurate mirrors. All mirrors have to be pretty close to the same width otherwise the raster lines are shorter or longer than they should be. Have to leave a small adjustment gap about 0.005 inch between mirrors to accomodate shorter or longer mirrors which hopefully will be where the retrace takes place and the gap will not reduce picture information. Have to buy the mirrors, too hard to cut square and of the same width. At the moment I am using ordinary mirror glass.
To date I have 8 raster lines of roughly similar widths about 2.5 inches on a screen 2 feet from the polygon. Everything is lined up with books pieces of wood and paper shims and is hard to work on. Make one adjustment and the slightest touch puts other mirrors out of alignment. Will look at a solid mirror platform soon. It is very satisfying to see the polygon revolving and a few raster lines on the screen.

[remp]

Greetings. I have now made a good solid mirror table from some heavy 1 inch formica covered wood. Sealed the edges and drilled 3 undersize holes for some 1/4 inch fine pitch bolts and forced them into the wood and the bolts cut a thread in the wood. Little bit of candle grease on the threads. Now I can adjust the bolts easy for setting the mirror table level with the polygon. Plan to make a new modulator. I have been using a 330 ohm 10 watt resistor from a 25-30 volt regulated supply with a milli amp meter feeding the laser with constant (adjustable) current. The 5 mw laser works from 50 milli amp to 90 milli amp. Other laser diodes may be different. Do not rely on guessing the maximum current. Laser diodes will stop working if the current exceeds the maximum even for a very brief time. Modulation was by putting a transistor in between the laser diode and ground. Worked ok and the laser could never get too much current. Changing that to putting the modulation transistor across the laser diode so when the transistor is off the laser gets all the current and when the transistor is fully on the laser gets no current. Its called current stealing and is one of the safer ways of powering a laser diode. The advantage of the change is I can set the lasing threshold easier. I will also replace the 330 ohm resisitor with 2 resistors and a 12 volt zeener diode from the midpoint to ground. That is in case my regulated supply fails and puts out too much voltage. The first modulation will be the usual horizontal sync pulses I have been doing for the last several days to identify tv lines and a second modulation of gradually lowering the laser current over 10 tv lines from full to minimum . This is to see if I am looking at 10 consecutive tv lines rather than several lines on top of each other.

[remp]

Greetings. Have installed the new laser diode modulator as described in the previous post and it works ok. It is a 2n2102 NPN transistor across the 5 mw laser diode and biased so just not conducting. In that condition the laser diode has 90 ma of current and is producing a laser beam. When I apply sync pulses to the modulation transistor it turns on, takes most of the current from the laser and this shows as a period of no laser light. The light on a screen from the single sided mirror on top of the polygon thus shows up as a red line with a black portion equivalent to the sync pulse. As mentioned in the last post I wanted to verify I was seeing individual raster lines not several lines on top of each other. My tv signal generator puts out video plus sync pulses with a selection of patterns. The easiest pattern to identify is a black screen with a single horizontal line halfway down. Using this I saw very dim raster lines until the horizontal line came into view and that one was bright just as it should be.
So far I have used the following equipment
0-12v power supply for polygon motor
0-30v power supply for laser
polygon motor with 8 facet mirror and home made single sided mirror mounted on motor shaft.
8 small mirrors fitted into wooden mounting blocks
Sturdy adjustable mirror table.
Small white screen (a4 envelope)
5 Mw red laser diode
single transistor modulator.
Squarewave signal generator to drive polygon motor
TV signal generator for sync pulses and video mudulation

Best results so far
8 vertical raster lines of poor quality with discernable modulation.

The 5 mw red laser diode gives visible raster lines in a darkened room. The quality from my laser diode is not very good but it can be modulated easily and beam quality may be able to be improved perhaps with a short lenght of fibre optic and some type of lens. The mirrors are extremely touchy to adjust.

In my experimenting I have found one very important fact. The light from a laser beam does not reduce in proportion to the number of raster lines. I presently have on the walls of my workshop 300 or so tv lines (one tv field) one after another and identified by a horizontal sync pulse and each line is about half the brightness of the original laser beam. All the lines are the same brightness and they are definitly not original light/300. If that were the case I probably would not see them at all but I can see them even with some ambient. Some lines have modulation which is clear and discernable so the lines are individual, not several lines on top of each other. That result is even more interesting because the lines on the wall are reflected from a rotating single sided household type mirror on the polygon so the refresh rate is only 50 percent.
So far, in this low cost small scale test of a laser projector I am happy with results.

[remp]

Hi there. Today I wanted to confirm the speed of the polygon motor by reflecting the laser beam off the polygon into a detector and counting the pulses. Set up a photodiode in front of the 8 factory mirrors on the polygon. Ran the motor at what I thought was 1500 rpm. Obtained a reading of 200 pulses per second from my frequency counter. 200 puses per second times 60 equeals 12000 and divided by 8 because there are 8 mirrors on the polygon gives 1500 RPM. Did the same setup on the DIY single sided mirror which gave 25 pulses per second times 60 equeals 1500 RPM. This confirmed that when I give the drive electronics for the polygon motor a squarewave at 1500 per second from my signal generator I get 1500 RPM from the motor. I thought that was good thinking by the polygon manufacturer to give a direct 1:1 correlation between drive in Hz and motor speed in RPM. Panasonic motor type MASQ8B24RM1 fitted with 8 sided mirror polygon. Motor runs up to 2000 RPM on 12 vdc Higher speed needs 24 vdc. The motor is rated at 24 vdc. Squarewave input 10 v peak to peak. One side of motor electronics input is ground. A 555 ic should run these motors ok.

[Evaas]

I'm having trouble understanding what all the mirrors are doing - specifically how do you get one horizontal line to be higher or lower than another. would it be possible to post a picture somewhere?