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'Looking for laser diode drive circuit'
1998\10\15@130417 by Philip Starbuck

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I am looking for a laser diode drive circuit that will allow me control a laser diode as will as provide the feedback control for the device.  I will supply logic level signals of 0.5 to 1 mS to the control circuit from a PIC to turn the laser diode off and on.  I would appreciate any circuits and or insight into doing this.

cheers,

Philip Starbuck


"There are three principal ways to lose money.  Wine, women, and engineers.  While the first two are more pleasant the third is by far the more certain."
                                               -- Baron Rothschild
                                                       ca. 1860

1998\10\15@142217 by Bob Blick

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Hi Philip,

I took this as an ascii-art challenge. I recommend Ultra-Edit for
ascii-art!

This circuit is awful, but it will get you started. It should work with
~millisecond pulses, but not ~microsecond pulses. I didn't know what you
were suggesting. If you need automatic power control AND microsecond
pulses, I'd suggest Analog Devices line of laser driver chips.

Here goes. Note that "GO" is the control pin, high = on. This circuit is
very supply voltage sensitive and I would never use it in a commercial
design, but then, I can't give you any of those designs.

You didn't say whose laser diodes you were using - there are four
different configurations, this circuit shows and uses the most common
polarities.

(+5v)---------o------------------
             \                 |
             /                 |
             \ 510             |
             / ohm           -----
             |               ^   v
             \           PD  |   |  LD
              >|             |   |
         PNP   |-----o--------   \
              /|     |           /
             /       \           \  4.7
          |/         /           /  ohm
(GO)--\/\/-|  NPN     \ 4.7K      |
          |>         /           |
     100K   \        |         |/
             o-----------------|    NPN
             |       |         |>
             \       \           \
             /      -/->         |
             \ 10K   \  10K      |
             /       /  trim     |
             |       |           |
(-)-----------o-------o------------

That doesn't look so bad!
Cheers,
Bob


On Thu, 15 Oct 1998, Philip Starbuck wrote:

>  I am looking for a laser diode drive circuit that will allow me control
a  laser diode as will as provide the feedback control for the device.  I
will  supply logic level signals of 0.5 to 1 mS to the control circuit
from  a PIC to turn the laser diode off and on.  I would appreciate any
circuits and or insight into doing this.

1998\10\15@162418 by Sean Breheny

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[WONDERFUL ASCII ART AND EXPLANATION SKIPPED]

I'm sure one of you could answer this for me: Why do laser diodes require
light intensity feedback (thru the internal photodiode)? I have hooked one
up without that (just direct pulses being fed to the LD thru a resistor)
and it worked fine (as far as I could tell).

Thanks,

Sean


+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
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1998\10\15@172315 by Dave VanHorn

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>I'm sure one of you could answer this for me: Why do laser diodes
require
>light intensity feedback (thru the internal photodiode)? I have
hooked one
>up without that (just direct pulses being fed to the LD thru a
resistor)
>and it worked fine (as far as I could tell).


So that with all combinations of temperature and such, you don't go a
TEENSY bit over the max, and toast the diode.  It's not the absolute
current that fries them, it's the optical flux blowing facets off.

BTW: I picked up a laser power meter at the last ham swapmeet I went
to :) :) :)  Working too!

1998\10\15@173736 by Bob Blick

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On Thu, 15 Oct 1998, Sean Breheny wrote:
> I'm sure one of you could answer this for me: Why do laser diodes require
> light intensity feedback (thru the internal photodiode)? I have hooked one
> up without that (just direct pulses being fed to the LD thru a resistor)
> and it worked fine (as far as I could tell).

Hi Sean,
The laser diode just acts like a limp LED below its laser threshold
current. Above that threshold, the output rises by a dramatic amount
with only slight increase in current. The diode can be injured by too much
light output OR too much current, so it's touchy. Also, the sensitivity to
temperature is also quite dramatic. If you don't have temperature control
you pretty much need to use the photodiode in a feedback loop, or run at
room temperature and be very careful of the current.

Late-model diodes are much better than old-timers(cheaper too).

Cheers,
Bob

1998\10\15@181707 by Dan Larson

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On Thu, 15 Oct 1998 14:31:24 -0700, Bob Blick wrote:

>On Thu, 15 Oct 1998, Sean Breheny wrote:
>> I'm sure one of you could answer this for me: Why do laser diodes require
>> light intensity feedback (thru the internal photodiode)? I have hooked one
>> up without that (just direct pulses being fed to the LD thru a resistor)
>> and it worked fine (as far as I could tell).
>
>Hi Sean,
>The laser diode just acts like a limp LED below its laser threshold
>current. Above that threshold, the output rises by a dramatic amount
>with only slight increase in current. The diode can be injured by too much
>light output OR too much current, so it's touchy. Also, the sensitivity to
>temperature is also quite dramatic. If you don't have temperature control
>you pretty much need to use the photodiode in a feedback loop, or run at
>room temperature and be very careful of the current.

My questions:  Is light intensity directly or inversely proportional to temperat
ure?
              What effect does temp have on the level at which the laser is dam
aged?


>
>Late-model diodes are much better than old-timers(cheaper too).
>
>Cheers,
>Bob
>

Dan

1998\10\15@193147 by John Griessen

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-----Original Message-----
My questions:  Is light intensity directly or inversely proportional to
temperature?



It's a moving target.  It's sort of directly proportional while you are in
the laser
functioning range of energy flow, but heat builds slower than light up to
the failure point.

THIS is probably what you are asking for:  I forgot whether the ambient
temperature is positively or negatively proportional to the desired pulse
energy.  I make a SWAG that it takes less energy to get in the laser mode
when cooler.
(The heat would steadily deteriorate the stored e- band states in the laser
material that would otherwise be available to amplify light waves, so more
pumping energy would be needed than when cool)

The feedback opportunity using
the photodiode built in is such a deal.  Without it, in the eighties,
I made a successful laser diode pulser that worked without feedback
(at least while running).  There WAS feedback--in the calibrate and
resistor selection process of manufacturing a power supply for the pulser
that put out a voltage dependent on temperature, matched at three
temperatures.

              What effect does temp have on the level at which the laser is
damaged?

1998\10\15@194155 by Bob Blick

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On Thu, 15 Oct 1998, Dan Larson wrote:
> My questions:  Is light intensity directly or inversely proportional to temper
ature?
>                What effect does temp have on the level at which the laser is d
amaged?

More heat = less light.

The diode is damaged by too much light output or too much current or too
much heat. Combining them seems to kill the diodes nicely! Really, it's
hard to say how much each has an effect. If you get can cool a diode, you
can run it at the absolute max output quite well. If it's hot, you'll
overcurrent it before getting much output. For some representative graphs
of some really rugged diodes, look at:
http://www.rohm.co.jp/products/shortform/20laser/laser3.html

-bob

1998\10\16@082127 by org Hager

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On Thu, 15 Oct 1998, Philip Starbuck wrote:

> I am looking for a laser diode drive circuit that will allow me control
> a laser diode as will as provide the feedback control for the device.  I
> will supply logic level signals of 0.5 to 1 mS to the control circuit
> from a PIC to turn the laser diode off and on.  I would appreciate any
> circuits and or insight into doing this.

Useful information on laser diodes can be found at:

http://www.repairfaq.org/sam/laserdio.htm


A lot of different driver circuits with explanations:

http://www.repairfaq.org/sam/laserdps.htm


Btw, I'm planning to build a PIC-based clock (similar to the rotating LED
designs) which projects the time to a wall using a laser diode. Does
anyone have experience with the mechanical setup for such a thing? After
all one has to rotate the diode on two perpendicular axes. I thought to
use a DC motor with a mirror on the vertical axis (running free, or
perhaps with a simple rpm regulator) and a stepper motor for the
horizontal axis. The diode would then be mounted on the stepper. Is there
a better way?

TIA,
Georg.

1998\10\16@082152 by Peter L. Peres

picon face
On Thu, 15 Oct 1998, Dave VanHorn wrote:

> BTW: I picked up a laser power meter at the last ham swapmeet I went
> to :) :) :)  Working too!

What range ? I'd like to get hold of a cheap one that covers 0-10 mW with
0.1 or better resolution.

Peter

1998\10\16@105627 by Richard A. Smith

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On Fri, 16 Oct 1998 09:22:50 +0200, Georg Hager wrote:

>Btw, I'm planning to build a PIC-based clock (similar to the rotating LED
>designs) which projects the time to a wall using a laser diode. Does
>anyone have experience with the mechanical setup for such a thing? After
>all one has to rotate the diode on two perpendicular axes. I thought to
>use a DC motor with a mirror on the vertical axis (running free, or
>perhaps with a simple rpm regulator) and a stepper motor for the
>horizontal axis. The diode would then be mounted on the stepper. Is there
>a better way?

First, don't try to move the laser diode.  Aim the beam at 2 small mirrors mount
ed 90 degrees to each other.  Then move the
mirrors.

Second, good luck... Drawing text via lasers requires a mechanical system with a
very fast response time and a resonant
frequency in the 100's of Hz.

What you are going to find is that unless you have a system with really low iner
tia when you attempt to stop the dot from
moving or change direction it will resonate and blur your text.  Scan rate is al
so another issue.  Make sure you can crank out
enough points/second so that you can actually see what is being drawn.  Try to g
o for a refresh rate of at least 10 - 15 Hz
preferably much greater.



--
Richard A. Smith                         Bitworks, Inc.
.....rsmithKILLspamspam@spam@bitworks.com               501.521.3908
Sr. Design Engineer        http://www.bitworks.com

1998\10\16@111558 by Peter L. Peres

picon face
imvvho you need a very beefy diode to make your clock visible in daylight
like this. Making some assumptions, the duty cycle for each dot will be in
the vicinity of 1:(5*7*4) ~= 1:140.

A bank of 5 or 7 diodes and a different scanning scheme will improve this
but at a price.

Peter

1998\10\16@115634 by Dave VanHorn

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>> BTW: I picked up a laser power meter at the last ham swapmeet I
went
>> to :) :) :)  Working too!
>
>What range ? I'd like to get hold of a cheap one that covers 0-10 mW
with
>0.1 or better resolution.


Two ranges, 0-9.99, and 0-99.9  It was sitting there with nobody
interested at all.
Needless to say, I snagged it at high speed :)

1998\10\16@212736 by Mark A Moss

picon face
I think it has something to do with the temperature coefficient of the
laser output.  For many laser diodes, the power varies so greatly with
temperature that a drive signal that produces typical output at 25C will
have no output at 0C and would self destruct at 50C.  There are probably
other answers as well.


Mark Moss
Amateur Radio Operator, Technician, and General Tinkerer


On Thu, 15 Oct 1998 16:22:03 -0400 Sean Breheny <shb7spamKILLspamCORNELL.EDU>
writes:
{Quote hidden}

Mark Moss
Amateur Radio Operator, Technician, and General Tinkerer

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1998\10\17@004336 by Andy Kunz

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>I'm sure one of you could answer this for me: Why do laser diodes require
>light intensity feedback (thru the internal photodiode)? I have hooked one
>up without that (just direct pulses being fed to the LD thru a resistor)
>and it worked fine (as far as I could tell).

They don't.  You use it to prevent frying them.  They are temp sensitive.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\10\17@090254 by Peter L. Peres

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On Sat, 17 Oct 1998, Mark A Moss wrote:

> I think it has something to do with the temperature coefficient of the
> laser output.  For many laser diodes, the power varies so greatly with
> temperature that a drive signal that produces typical output at 25C will
> have no output at 0C and would self destruct at 50C.  There are probably
> other answers as well.

You are almost right. The next time you have a visible laser diode
assembly with PSU in your hands, use electronics freeze spray on it while
keyed on (from the side). The temperature drop from +30 deg. C (my case
here) to -50 deg. C (according to the freezer leaflet I have here) causes
at least a two-fold increase in output before the window fogs over.

The trick also works with common LEDs. SMT LEDs soldered on ceramic work
best ;) The ultra bright orange kind becomes so bright it hurts to look
into it even without a lens, at If ~= 8 mA !.

Be sure not to freeze your fingers off if you do this, and know that some
laser pointer plastics won't take -55 C. Use this at your own risk.

Anyway, the original experiment involves liquid nitrogen, which gives even
MORE output. The method also works with IR LEDs and lasers of course. The
first semiconductor lasers worked in liquid nitrogen at 77 K according to
my books.

Peter

PS: Lasers operated in closed circuit do not have such a strong response
on temperature, but power requirements drop with dropping temp. and the
laser radiation is cleaner (coherence, bandwidth).

1998\10\17@104136 by paulb

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Peter L. Peres wrote:

> What range ? I'd like to get hold of a cheap one that covers 0-10 mW
> with 0.1 or better resolution.

 I wonder what the sensor is?  My "gut feeling" is that you could make
it easily and calibrate it from a reference meter, presuming you can
"con" one.

 I would assume a suitable sensor to be a large area photodiode at the
end of a black pipe.  By "suitable", I mean linear response and
beamwidth independent.  An alternative, self-calibrating, might be a
bolometer.

Richard A. Smith wrote:

> First, don't try to move the laser diode.  Aim the beam at 2 small
> mirrors mounted 90 degrees to each other.  Then move the mirrors.

 The mirrors may be at 90¡ if you want to send the beam back over the
laser, or parallel if you want it to return to the original direction.
What they must be is *close*.

 You know, the design is just as complex to do it on your room wall as
to get a 5W laser and go into the laservision business!

> Second, good luck... Drawing text via lasers requires a mechanical
> system with a very fast response time and a resonant frequency in the
> 100's of Hz.

 Like in a hard disk, but they're hard to come by second hand, aren't
they?

> What you are going to find is that unless you have a system with
> really low inertia when you attempt to stop the dot from moving or
> change direction it will resonate and blur your text.

 Back to the PID thread.  Oh dear!

 Hint: Think *round* numbers, *not* square.  Whether you need to gate
(switch on and off) the beam depends on various things, including the
maximum acceleration.

> Try to go for a refresh rate of at least 10 - 15 Hz, preferably much
> greater.

 Depends on various things; one is whether it is going to annoy you if
it flickers.  Dear me, I can't remember whether flicker is more
noticeable in dim light (as a nightlight/ night club) or bright.  For
impressing friends/ patrons, I suspect it is not critical ;-)

 I am assuming it to be patently obvious that if you can settle for
less efficiency, surplus raster displays are legion.
--
 Cheers,
       Paul B.

1998\10\18@162701 by Dave VanHorn

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 I wonder what the sensor is?  My "gut feeling" is that you could
make
it easily and calibrate it from a reference meter, presuming you can
"con" one.


Looks like a solar cell, about .25" square. It will show a few mW
indication in sunlight or under a bright lamp. As far as calibration,
I'm not sure, but my 5mW pointers are reading about 4.8mW, so I guess
it's in the ballpark.

1998\10\19@080109 by Pavel Korensky

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At 09:49 15.10.1998 -0700, you wrote:
>I am looking for a laser diode drive circuit that will allow me control a
laser diode as will as provide the feedback control for the device.  I will
supply logic level signals of 0.5 to 1 mS to the control circuit from a PIC
to turn the laser diode off and on.  I would appreciate any circuits and or
insight into doing this.
>

There is whole laser diodes FAQ on the Net. With schematics, parameters etc.
I downloaded mine form filipg page on Paranoia server, approx. year ago.

PavelK

**************************************************************************
* Pavel KorenskyÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ *
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**************************************************************************

1998\10\19@113725 by Peter L. Peres

picon face
On Sun, 18 Oct 1998, Dave VanHorn wrote:

>   I wonder what the sensor is?  My "gut feeling" is that you could make
> it easily and calibrate it from a reference meter, presuming you can
> "con" one.

It's a photodiode. The trick is, it has to be thick so as not to saturate
anywhere within the beam cone.

Peter

1998\10\20@031033 by
flavicon
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> >   I wonder what the sensor is?  My "gut feeling" is that you could make
> > it easily and calibrate it from a reference meter, presuming you can
> > "con" one.
>
> It's a photodiode. The trick is, it has to be thick so as not to saturate
> anywhere within the beam cone.
>
> Peter
>
We use shedloads of optical power meters here at work.  According to the HP
docs I have here, it is a germanium sensor.  They aren't very cheap
either....a wide area power head can cost as much as the actual meter.  The
problem is power and wavelength linearity and dynamic range.  A bog standard
photodiode is extrememly wavelength dependant.

I had a look to see what laser drivers are used in our products, but they
are all in-house designed and manufactured as they are a bit of a
specialised item (modulation rates up 2.4GHz) so not too usefull for you.

Regards

Mike Rigby-Jones
EraseMEmrjonesspam_OUTspamTakeThisOuTnortel.co.uk

1998\10\21@114136 by Peter L. Peres

picon face
On Tue, 20 Oct 1998, Rigby-Jones, Michael [PAI01:4837:EXCH] wrote:

> > >   I wonder what the sensor is?  My "gut feeling" is that you could make
> > > it easily and calibrate it from a reference meter, presuming you can
> > > "con" one.
> >
> > It's a photodiode. The trick is, it has to be thick so as not to saturate
> > anywhere within the beam cone.
> >
> > Peter
> >
> We use shedloads of optical power meters here at work.  According to the HP
> docs I have here, it is a germanium sensor.  They aren't very cheap
> either....a wide area power head can cost as much as the actual meter.  The
> problem is power and wavelength linearity and dynamic range.  A bog standard
> photodiode is extrememly wavelength dependant.

Hmm, I remember when I was a kid sawing off the cap of Germanium
transistors and using a lit cigarette and a multimeter ;) Germanium makes
a very good IR sensor. The magic with the sensors probably lies in the
antireflex coating and geometry, doping etc.

Peter

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