Searching \ for '[OT]: scanning laser projector' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/displays.htm?key=laser
Search entire site for: 'scanning laser projector'.

Exact match. Not showing close matches.
PICList Thread
'[OT]: scanning laser projector'
2004\04\29@132920 by Gary Fixler

flavicon
face
Let me start off by saying "this is just for fun."

I whittled away the shell of a very tiny keychain laser and soldered
in leads so it's PIC-ready. I want to build a small box with
motor-mounted mirrors in 2 directions to create a mechanical scanner
that draws a grid on the wall by reflecting the laser beam. I figured
some kind of light-sensor(s) being tripped each pass could trip a PIC
interrupt for sync. The problems I ran up against were motor speeds. I
imagine I'd sync the mirror blocks with a timing belt assembly. They
can't spin at the same speed, or I'd only be able to draw diagonals -
it would work out as though I had only one mirror, set at a diagonal.

If the mirrors were triangular blocks, such that every rotation was 3
mirror passes, and I wanted 30fps, then the Y block could spin at
10rps, or 60rpm. If I wanted 640x480, just as an example, the X motor
would need to scan horizontally 480 times for each pass in Y, which
would be 1440x for every Y block revolution. With the Y block @ 60rpm,
that would be 86,400rpm for the X block :)

I've tried to think of alternate ways of scanning, including tracing a
diagonal path that visits every pixel once (even if it skips around a
bit), but the math on that is a bit above me, and compounds the
software/video signal issue. I've dumbed down the resolution and
thought of things like interleaving. Maybe each pass in Y (one third
of Y block revolution) draws a separate 1/3 of the screen? I've also
pulled way back on the fps. By the time I was done, I had block rpms
in the low thousands, with something like 80x60 @ 6fps. I've also
considered more sides to the mirror blocks, but each new side
increases the radius, or decreases the side length.

I know there are some great minds on this list, so I thought I'd throw
the idea into the group and see what kinds of ideas came back. I'm not
totally sure what speeds PICs can handle, or how fast the interrupt
routine to flash the laser beam could work, or what kind of sensor
would pick up the sync signal at that kind of speed (phototransistor,
CdS cell?). Also, it would be nice if I could alter the brightness of
each dot to create a 'redscale' image. I tested the laser on 3v with a
2k pot, and I was able to dim the beam all the way to off. I'll be
able to run some experiments with flash timings to get values for the
brightness levels. I'm thinking I'd probably draw lines of on/off
instead of worrying about every individual pixel when it isn't
necessary.

Thanks for any suggestions or observations
-gary

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spam_OUTlistservTakeThisOuTspammitvma.mit.edu with SET PICList DIGEST in the body

2004\04\29@134415 by M. Adam Davis

flavicon
face
The only other consideration you might want to keep in mind is that the
display is going to be unbelievably dim.  Take the brightness of your
laser pointer, and divide that brightness by the surface area you'll be
covering.  You might get a reasonably bright image a few inches from the
scanner in a dark room.  It would still be fun to play with though.

You might instead consider using a vector method.  Instead of drawing
pixels, draw lines and arcs.  You can do this on the cheap with two
speakers and two mirrors.  Hinge the mirrors so it pivots on one edge,
and the other edge is connect to the cone of the speaker.  Now the
mirror will bounce the beam at an angle determined by the position of
the speaker.

Put two of these assemblies at right angles and you'll have a 2D
scanning assembly.

It's something I've wanted to do for awhile, but for lack of time.  Take
pictures and make a web page about it!

-Adam

Gary Fixler wrote:

{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamKILLspammitvma.mit.edu with SET PICList DIGEST in the body

2004\04\29@173418 by Robert Rolf

picon face
Old laser printers have the polygon scanning mirror you're trying
to build. Add a second strip mirror (or shaft with polished flat)
rotating at 3600 RPM for the vertical sweep, and you've got the mechanics done.

Pixel rates are in the Mhz for a typical laser printer (HP LJII or III).
You also get the needed 'start of sweep' sensor and speed control for free.

The down side is that any image you produce will be incredibly faint since
you are spreading a 10mW source (Class 3?`) over a HUGE area.
For sake of argument, say you have a 1mm diameter beam @ 10mW.
Now spread it over 1 square meter (1 million sq. mm) and you have
1 NANO WATT per mm. Can you read a page with a 1W bulb at 1 meter?
Your laser is hundredth the power.

Robert

Gary Fixler wrote:
{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email EraseMElistservspam_OUTspamTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

2004\04\29@173626 by Matthew Fries

flavicon
face
I had always wanted to see if you could use a laser in this manner for
exceptionally sharp television. I had thought of pretty much the same
mechanism as you, and considered other methods of beam "deflection".

One that may be better suited to your use of motors (rather than voice
coils on mirrors), might be a spinning prism. Such a method would reduce
retrace (if your still stuck on a rastar display rather than a vector
display), but I don't think the scan would be as linear.



On Thu, 29 Apr 2004, Gary Fixler wrote:

{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email @spam@listservKILLspamspammitvma.mit.edu with SET PICList DIGEST in the body

2004\04\29@175737 by Jason S

flavicon
face
It's not nearly that bad.  The wattage of a lightbulb is the total power
consumed by the bulb (most of which is lost as heat, not given off as
light).  For a laser, the wattage is the power emitted in the form of light.

Jason

----- Original Message -----
From: "Robert Rolf" <KILLspamRobert.RolfKILLspamspamUALBERTA.CA>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Thursday, April 29, 2004 2:33 PM
Subject: Re: [OT]: scanning laser projector


> Can you read a page with a 1W bulb at 1 meter?
> Your laser is hundredth the power.

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spamBeGonelistservspamBeGonespammitvma.mit.edu with SET PICList DIGEST in the body

2004\04\30@025911 by hael Rigby-Jones

picon face
>From: "Robert Rolf" <TakeThisOuTRobert.RolfEraseMEspamspam_OUTUALBERTA.CA>
>> Can you read a page with a 1W bulb at 1 meter?
>> Your laser is hundredth the power.

>From: Jason S [RemoveMEpicspamTakeThisOuTCANADASPEAKS.COM]
>It's not nearly that bad.  The wattage of a lightbulb is the
>total power consumed by the bulb (most of which is lost as
>heat, not given off as light).  For a laser, the wattage is
>the power emitted in the form of light.

It is that bad.  Robert was talking about radiant power, not consumed power.


Regards

Mike




=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================
Any questions about Bookham's E-Mail service should be directed to
postmasterEraseMEspam.....bookham.com.

--
http://www.piclist.com hint: To leave the PICList
EraseMEpiclist-unsubscribe-requestspammitvma.mit.edu

2004\04\30@030320 by David P Harris

picon face
Hi-
Check out this AVR site: http://heim.ifi.uio.no/~haakoh/avr/
David

Gary Fixler wrote:

{Quote hidden}

--
http://www.piclist.com hint: To leave the PICList
RemoveMEpiclist-unsubscribe-requestspam_OUTspamKILLspammitvma.mit.edu


'[OT]: scanning laser projector'
2004\05\02@112436 by Alexander Rice
picon face
On Fri, 30 Apr 2004 07:59:08 +0100, Michael Rigby-Jones
<RemoveMEMichael.Rigby-JonesTakeThisOuTspamspamBOOKHAM.COM> wrote:

>> From: "Robert Rolf" <EraseMERobert.RolfspamspamspamBeGoneUALBERTA.CA>
>>> Can you read a page with a 1W bulb at 1 meter?
>>> Your laser is hundredth the power.
>
>> From: Jason S [RemoveMEpicKILLspamspamCANADASPEAKS.COM]
>> It's not nearly that bad.  The wattage of a lightbulb is the
>> total power consumed by the bulb (most of which is lost as
>> heat, not given off as light).  For a laser, the wattage is
>> the power emitted in the form of light.
>
> It is that bad.  Robert was talking about radiant power, not consumed
> power.
>
>
> Regards
>
> Mike
>

You might want to look into more powerful diode lasers, preferably green
ones as your eye has higher sesnitivity (about 10* more a 525nm than at
650nm). I have a 10mW green laser and by shining this through things like
broken glass i have spread the beam over about 1m^2 which is about the
limit of good visibility in a darkened room, so for your 5mw red which is
about 20x dimmer it would suggest a limit of about 20 cm * 20 cm for
visibility in a dark room, which isn't too bad.

an interesting point was that i also used a stepper motor an a rather
unusual way, if you get a really small bipolar stepper motor with the
biggest step angle you can find (about 12 degrees is common) and then
drive one of the coils with DC and apply your signal to the other coil,
this results in a rotational movement between two step positions that is
actually pretty proportional to the applied signal, if you want you can
even implement a feedback system based on the back EMF induced in the DC
winding - this works far better than the more common speaker-mirror trick.

FWIW a 15W incandecent light bulb emits around 1W of visible light

Regards

Alex

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

2004\05\02@145335 by Robert Rolf

picon face
Alexander Rice wrote:
> an interesting point was that i also used a stepper motor an a rather
> unusual way, if you get a really small bipolar stepper motor with the
> biggest step angle you can find (about 12 degrees is common) and then
> drive one of the coils with DC and apply your signal to the other coil,
> this results in a rotational movement between two step positions that is
> actually pretty proportional to the applied signal, if you want you can

As long as you're in the middle 50% or so of a step. The endpoints
will be quite rounded.

> even implement a feedback system based on the back EMF induced in the DC

Not quite, because the feedback is also none linear, in the same way.
Better to have an external position sensor (differential capacitor
works well and is common in galvo scanners).

> winding - this works far better than the more common speaker-mirror trick.

And a lot easier to construct. In theory you could get
nearly 24 degree beam deflection. With tiny mirrors placed
very close together you could make a decent
but slow X-Y scanner.

You could set the DC coil drive to something less than spec to
lower the magnetic spring constant, making the unit more
sensitive. However this is a trade off between moving mass
and applied power (force). You also need to make sure it's
a DC (PM permanent magnet) stepper, not a variable reluctance unit.
(Easy to tell. Does is 'cog' when you turn the shaft without
applied power. If it does, it's PM).
I have tons of old Decwriter paper feed motors. I'll have
to give this one a try. The coil resistance is low enough that
it could be driven directly by an audio power amp.

Robert

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics

More... (looser matching)
- Last day of these posts
- In 2004 , 2005 only
- Today
- New search...