printing a message using tWO mirrorz and a single lazer

[zeshan]

hello i want to print a message on he screen using a single laser and two Octagonal mirrors (for horizontal and vortical movments) mounted on motors...............i am confued how to go for it....can any body help me plz?????????????????????????? me really need that.......

 

[betwixt]

It is quite difficult to do. You have to consider it as being a scanned image, rather like a TV picture.

The basic steps are:

1. Work out the horizontal scan rate and from there the speed the horizontal axis motor has to rotate.

2. Do the same for the vertical motor, usually this is much slower than the horizontal one.

3. Rasterize the message, in other words convert the lines into pixel coordinates.

4. At the start of each horizontal scan, reset a pixel counter. The counter will have to go up to the maximum number of pixels you want in each line.

5. Do the same for the vertical scan and counter.

6. Increment the horizontal counter as the horizontal motor rotates. It should reach maximum count at the end of the line. From that you can work out the frequency of the horizontal counter clock.

7. Do the same for the vertical motor and work out the vertical pixel clock frequency.

8. If the coordinates in your rasterized message are the same as the horizontal and vertical counter values, turn the laser on, at all other times it should be turned off.

You might find it easiest to derive the rasterizing clock, horizontal and vertical clocks from a single source, divided down to the appropriate frequency, this will help to keep the scan stable.

Good luck - it's easy to get an image but difficult to get the one you want!

Brian.

 

[ark5230]

This has to be achieved by the tilting of the mirrors rather than moving, reason being that the motion requires finite time and may not meet the reqirements of persistance of vision to allow for an acceptable image.
raoof

 

[betwixt]

Octagonal mirrors are usually configured in a cylinder with the motor axis in line with its center. They are intended to free run so they sweep a beam in a line eight times per motor rotation. I don't think they are suitable for vector drawing as ark5230 suggests.

Brian.

 

[zeshan]

what should i do then to get that??????????????? plz guide me its my FYP

 

[welove8051]

refer cornell university projects. https://courses.cit.cornell.edu/ee476/FinalProjects/

regards
kj
welove8051.com

 

[zeshan]

thanx Brain....actually first i want to get an image......................any sort of circle or triangle....i am confused about MOTORZ to be used for octagonal mirrorz.............how can i achieve Synchronization between orizontal n vertical scanz????? plz suggest

 

[betwixt]

To you don't have to synchronize the motors to each other but it makes the circuitry simpler.

What you must do though, is have a way of discovering the time at which the scans start. You can do this with a mechanical or magnetic sensor on the motor shafts but it may be easier to use a second light source (an LED will do) and a photo-sensor positioned so it sees a flash of light once per rotation.

Use the output of the sensor to reset the horizontal and vertical pixel counters, this gives you a known starting coordinate for each scan and allows the electronics and mechanical parts to stay in step with each other. You still need to keep the motor speeds as constant as possible otherwise the message will have jagged edges.

Brian.

 

[zeshan]

should i use Techometer for this purpose?????????????????????????? to calsulate or estimate revolutionz???????????????????

 

[betwixt]

No, the motor speeds are not critical, within sensible bounds but if you can keep the speed constant, whatever it is, it will help to keep the image still.

The idea of using the optical sensor is to know where the motor shaft is. If you can get one pulse from the sensor per sweep of the scan line you can use it to synchronize the electronics to the motor. As long as you can electronically predict where along the scan you are, you can tell when to flash the laser on and off.

For example:

Looking at the horizontal scan (same applies for vertical) and supposing you have 1000 pixels resolution along the line. The motor turns and the laser reflecting off the mirror draws a straight line. We can call the start of the line pixel 0 and the end of the line pixel 999 (1000 in total). Now use a electronic counter which clocks 1000 times in the duration of the line and reset it to zero with the sensor as the line starts.
You can now give a number to any location along the line, 0 is the start, 500 is half way and 999 is the end. By comparing the number with one from your rasterizing software, you can tell if that point along the line should be lit or dark and control the laser accordingly.

Brian.

 

[zeshan]

plz tel which microcontroller i should use for this purpose??????????????????????????????? n why?

 

[ark5230]

Zeshan, if you dont feel offended, I think it is a project with complexity difficult for you to handle. Try revising. Many things appear cool and interesting but are bit difficult to achieve.
Raoof

 

[zeshan]

i knw Raoof bhai but i hav selected this as my FYP....i cant change it nw.........i hav to do it so plz help me if u can.......................thanx