Status of Cheap DIY Laser Power Meters?

Dude, you need to get real about what is a "reasonable" price for such specialized equipment. Laser power meter heads are not mass produced like DVD players or other commodities that go down in price over time because of manufacturing improvements. They are very specialized sensors that require very high precision signal amplification to get right. The same technology that went into thermal heads in the 1970s is in the heads today. The only difference today is that thermal heads can detect beam positions and have their data built into the head itself. Even those are quite old, dating from the 90s.

The downside of such "improvements" is that now you can't connect your nice new coherent thermal head to your op-amp circuit via simple BNC connector, but instead need to have their special adaptors that can read off the data in their proprietary way.

You can expect that the price of such equipment will not go down simply for the fact that there is no reason to. These meters stay "good" for a long time, and can be recalibrated for far less than the cost of buying a new one. Furthermore, once you buy one, you don't need to get another until someone breaks it.

Laserbee's meter is about as close as you're going to get to a DIY-class meter of any reasonable accuracy and wavelength generality. The technology behind it isn't complicated, and you can get and assemble the parts if you put your mind to it. The thing is: it takes time and effort, and you need a reference meter to calibrate it with. It's the kind of thing that many people here don't have the patience to build or learn, so $150 for such a meter is a pretty good deal.

By the way, that "$600 Pentagon toilet seat" is a distorted legend. It refers to a mentioned estimate for the development + total manufacturing of specialized toilet seats on military aircraft, since such a toilet seat would need to withstand the mechanical wear of being on such an aircraft its long lifespan. The legend serves as an example of how stupid senators and the media latch onto such nonsense to serve their own interests.

seoguy said:

* The Benm diode-based design.  This one is still a little rough around the edges, but got me to thinking about ideas for possible enhancements.  Anyone using this, and how does it compare with the old thermopile design?

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I suppose it does need some refinements A couple of people have attempted building them, but accuracy remains limited no matter how you set up the sensor.

One thing that is somewhat problematic is the slow response - you need to heat the sensor plate to equilibrium to get the reading. This could be improved vastly by adding a microcontroller based readout, since the temperature (and power readout) climbs asymptotically towards its final value, and this can be predicted from a few measurements.

As for the sensor itself: making it smaller would improve speed too, but it has to be large enough to catch the entire beam - so even swapping for tiny smd components goes only so far. Accuracy (and lower range) could be better using temperature sensors instead of the 1n4148 diodes i used in the example.

Above issues being as they are, the way the measurement works is comparable to a thermopile, and wavelength response only depends on how black you can get the sensor plate. Using anodized aluminium from a heatsink, it has no problems measuring the thermal radiation from your pizza oven, as long as the reference diode is not illuminated by it.

Bionic-Badger said:

Dude, you need to get real about what is a "reasonable" price for such specialized equipment.  Laser power meter heads are not mass produced like DVD players or other commodities that go down in price over time because of manufacturing improvements.  They are very specialized sensors that require very high precision signal amplification to get right.  The same technology that went into thermal heads in the 1970s is in the heads today.  The only difference today is that thermal heads can detect beam positions and have their data built into the head itself.  Even those are quite old, dating from the 90s.

The downside of such "improvements" is that now you can't connect your nice new coherent thermal head to your op-amp circuit via simple BNC connector, but instead need to have their special adaptors that can read off the data in their proprietary way.

You can expect that the price of such equipment will not go down simply for the fact that there is no reason to.  These meters stay "good" for a long time, and can be recalibrated for far less than the cost of buying a new one.  Furthermore, once you buy one, you don't need to get another until someone breaks it.

Laserbee's meter is about as close as you're going to get to a DIY-class meter of any reasonable accuracy and wavelength generality.  The technology behind it isn't complicated, and you can get and assemble the parts if you put your mind to it.  The thing is: it takes time and effort, and you need a reference meter to calibrate it with.  It's the kind of thing that many people here don't have the patience to build or learn, so $150 for such a meter is a pretty good deal.

By the way, that "$600 Pentagon toilet seat" is a distorted legend.  It refers to a mentioned estimate for the development + total manufacturing of specialized toilet seats on military aircraft, since such a toilet seat would need to withstand the mechanical wear of being on such an aircraft its long lifespan.  The legend serves as an example of how stupid senators and the media latch onto such nonsense to serve their own interests.

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Well said... BB...

@seoguy....
as to the picture of the "archaic sensor"... the same Thermo-couple technology is being
used today on Lab Quality Thermopile heads... that cost so much..  

Jerry

goamarty, you have to remember that these were being marketed as a non-lethal weapon, like a taser, not as a pointer. I was more concerned about their being used as a replacement for a cop's flashlight in a "let's see how red your eyeballs are", or as a pupil dilation response test!

You probably won't be able to make your own LPM for cheaper than you can buy them...

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I disagree. For example, it looks like Benm's design would cost well under $50 to make!

You should try posting on the BST section that you want to buy a power meter...

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No, I shouldn't - because I am not looking to buy one.

you need to get real about what is a "reasonable" price...

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What is a reasonable price for NASA or the military is not the same as what is reasonable to an individual hobbyist that does not have a multi-million $ budget. For instance, the Pentagon thought $1,100 each for a ~50mw greenie was a "reasonable" price.:

for such specialized equipment...very specialized...

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You sound like you are writing a marketing brochure for an overpriced product! : Just because something is highly specialized - that is, designed for a very specific purpose - does not make it expensive. Toenail clippers are also highly specialized equipment. So is the mechanism inside of a cheap DPSS laser.

...that require very high precision signal amplification to get right.

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You seem to be implying that an expensive very high precision signal amplifier is required to "get it right", thus justifying the high price. That is simply not the case.

The level of precision required is not "very high" by today's standards, and is easily affordable by any hobbyist. For example, the DIY design based on the eBay surpl. sensors used a signal amplifier extracted from the original device. When a couple people complained that the chip on theirs was "dead", someone pointed-out that you can now buy the necessary "precision" amplifier, brand-new for only a few dollars!

Indeed, someone is now selling the exact same "precision" amplifier that was being used in those heads on eBay, for $2.50 brand-new! -

http://cgi.ebay.com/LTC1050-Precision-Zero-Drift-Op-Amp_W0QQitemZ380086090497QQcmdZViewItem

It is also worth noting that such high levels of amplification were required in those meters to compensate for the very low signal strength coming from those antiquated low-junction-count bimetal sensors. More modern thermopile devices generate a much better signal to begin with, and thus do not need such high-level amplification to compensate for their shortcomings.

Laser power meter heads are not mass produced like DVD players or other commodities that go down in price over time because of manufacturing improvements.

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Mass-production is not the only thing that dramatically lower costs over time. So does improvements in technology, as well as reduction in the costs of the electronic components that make up the product (case in point - the LTC1050 referenced above). And I would venture to say that technology has advanced slightly over the last 30 years!

Regarding a few of your other claims...

The fact that a product does not go "bad" over time (what are we talking about here, fish? ;D ) does not make it expensive. :

That a product is not disposable like Kleenex, does not make it expensive. :

That they can be "recalibrated for far less than the cost of buying a new one", is just another way of saying that these products are extremely expensive, compared to the cost of the periodic maintenance that these pricy devices also require. I don't see that as an advantage!

The same technology that went into thermal heads in the 1970s is in the heads today.

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Gosh, I hope not, or this market is in worse shape than I realized!

It is not unusual for specialized vertical-market products to be based on older technologies. This does not mean that those technologies are therefore superior for that application, only that because competitive pressure is less (or in some cases, non-existent), the products in that market have yet to catch up with the rest of the world technology-wise.

Given the significant improvements in thermopile technology since that antiquated device, if this is true, it would mean that not only are these commercial meters very expensive, they are also severely out-of-date!

It would also mean that, by utilizing more up-to-date technology, a DIY design would be far more likely to achieve an acceptable level of performance at a greatly reduced cost!

Thanks, you just gave us a Real Good Reason to pursue a DIY approach!

And on some of your claims attempting to dissuade us from even thinking about pursuing a DIY meter -

Laserbee's meter is about as close as you're going to get to a DIY-class meter...

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I don't see any detailed schematics, or components lists, or PCB trace designs, or bare boards, or parts kits...that is not even close to a LPF DIY project - those are lower-end commercial products!

so $150 for such a meter is a pretty good deal

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It might be, if such a thing existed. But of the links posted, the thermal meter I saw with a case cost nearly twice that.

In any event, I already reviewed those links, and while they might be fine products, I indicated that they did not match my particular needs.

and you need a reference meter to calibrate it with

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From what people have said about old thermal heads (or even entire used meters), unless you are willing to buy brand-new, that issue is not limited to just DIY designs.

Depending on the design, even an uncalibrated meter may be accurate enough for some people's needs. And, of course, it can also be used to compare relative power levels of different lasers!

I also recall a thread by some of the folks here who had the thermal DIY meters based on those old surpl. heads, who came up with the idea of passing-around a "reference source" laser, so they could self-calibrate their own meters!

With a DIY approach, there may also be ways to mitigate this issue. For example, Benm's design incorporates a unique auto-calibration capability. And sensor devices based on more advanced technologies (that are more recent than Watergate & the Vietnam War! :), may not be so subject to drift, or may even come from the factory essentially pre-calibrated!

And I saved your most ridiculous claim for last...

The thing is: it takes time and effort...
It's the kind of thing that many people here don't have the patience to build or learn

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Are you kidding??? This web site is populated by folks whose primary motivation seems to be pursuing new DIY builds. I have seen some truly amazing feats accomplished by members here!

And in this forum section especially - Experiments & Modifications - which is dedicated to those who want to go beyond the simple DIY tutorial builds, to pull out their toolkit, or optics, or soldering iron, or lathe, or superglue, or breadboard, and dig in, the experimenters, the tinkerers, the scientists, the inventors, the do-it-yourselfers.

And yet you claim that soldering a few components together and building a simple meter is beyond the skill level and mental capabilities of most of the people in here???

I'm sorry you have such a low opinion of the patience and capabilities of your fellow forum members!

Once we have a design fine-tuned, I don't see this project requiring any greater skill than what is required for many of the other projects I have seen in LPF. In fact, it should be even easier, as you won't have to worry about fitting everything inside a host!

And rather than the naysayers who seem to be trying to convince me to completely abandon this project, and who want to tell us all the reasons why they think something CAN'T be done, I would prefer folks who engage in the much more intellectually challenging task of thinking about how it CAN!

as to the picture of the "archaic sensor"... the same Thermo-couple technology is being
used today on Lab Quality Thermopile heads... that cost so much..

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All the more reason to avoid it then! Thermopile technology has advanced considerably since Sony's introduction of the Betamax!

Even the thermal sensor you are using appears more modern than that!

That reminds me, I asked you a question in a previous post in this thread, but you must have missed it, as you never gave us a reply -

"By the way, that heat sink/sensor pic in the thermal-based meter you linked to is an excellent example of the kind of quality DIY head I was talking about! What make/model thermopile device is that using?"

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Here is the pic I was referring to -
http://www.bauer-electron.com/ebypics/dlb01.jpg

Thanks!

Using anodized aluminium from a heatsink, it has no problems measuring the thermal radiation from your pizza oven...

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LOL ;D (and probably a lot less expensively than those used laser heads too!)

Benm, I think that your design has the most potential out of any of the DIY designs I have seen to date!

I did notice from the thread that there were still a few design issues to be resolved, but that whole concept really got me to thinking, and like I told 691175002, I have a few ideas I would like to share about that, once I have had a chance to refine them a bit!

But I definitely congratulate you on what you did there! (even more so that you resisted the pressure here to use a commercial head!)

You appear to be trying to use the forum members here as your personal R&D department.  

"Rah -- Rah!"  "You can do it, guys" may work well IF you are paying them to do it.  However, with most members here, you will need to do some work and present what you've done before others will spend their time trying to help you.

"Naysayers" have value too.  They usually point out the major challenges to be overcome.

If you want to be a part of the community here, you must be a "member" of the team, NOT the "coach."

Peace,
dave

I did notice from the thread that there were still a few design issues to be resolved, but that whole concept really got me to thinking, and like I told 691175002, I have a few ideas I would like to share about that, once I have had a chance to refine them a bit!

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I'm looking forward to seeing any refinements you are able to make!

I constructed the initinal prototype for this meter on a breadboard using only components that i had laying around here already. The idea for the sensor i've seen somewhere else, but i dont really remember where or even if it was for this application.

The only thing that changed is the case its in (windproofing it a little bit), and the component values allowing 1 mV/mW output signal so a simple multimeter can be used. It still doesnt contain a single component i had to buy specially for it - which makes it easy to reproduce for anyone and tinker as they like

I think the best improvements i can make to it are mostly digital, using a microcontroller to improve response and such, but that would make it more difficult to reconstruct... unless you have some electronics kit already, such as a programmer. Next thing i'll try is to use a pic16f877's builtin a/d converters to sample the signal, but i'm not sure it'll work well yet

seoguy said:

1)....

Laserbee's meter is about as close as you're going to get to a DIY-class meter...

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I don't see any detailed schematics, or components lists, or PCB trace designs, or bare boards, or parts kits...that is not even close to a LPF DIY project - those are lower-end commercial products!

2)....

so $150 for such a meter is a pretty good deal

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It might be, [highlight]if such a thing existed[/highlight].  But of the links posted, the thermal meter I saw with a case cost nearly twice that.

3)......
With a DIY approach, there may also be ways to mitigate this issue.  For example, Benm's design incorporates a unique auto-calibration capability. And sensor devices based on more advanced technologies (that are more recent than Watergate & the Vietnam War! :), may not be so subject to drift, or may even come from the factory essentially pre-calibrated!  


4).....
[highlight]And I saved your most ridiculous claim for last...[/highlight]

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1).........
            No one ever said that the LaserBee I was a DIY project... :
            And you will never see the LaserBee Schematics or Components lists, or PCB trace designs.

2).........
            Yes... the LaserBee Exists :-? and off eBay you can get one for $159.99 plus shipping.. :-?

3)........ "Benm"... actually...needed to have another member test a red calibration laser with a
           Laser Power Meter to be sure of his measurements... so you're a little off there...
           And to be sure that your DIY  theories, circuits and calculations are giving you the correct
           output... you WILL need a calibrated LPM... no mater how you slice it...

4)........ So basically... you are saying... that everything contrary to your way of thinking is
           RIDICULOUS.... :-/

In your overly lengthy posts.....you keep harping on the New Thermopile Technology.....
Show us.. that new non-archaic Thermopile Technology that is being used by companies like
Coherent or Newport... or any other commercial LPM manufacturer.... that you speak of...:-?

I'm willing and eager to learn about and see this new technology as others here are as well...

Jerry

seoguy said:

as to the picture of the "archaic sensor"... the same Thermo-couple technology is being
used today on Lab Quality Thermopile heads... that cost so much..

Click to expand...

All the more reason to avoid it then!  Thermopile technology has advanced considerably since Sony's introduction of the Betamax!

Even the thermal sensor you are using appears more modern than that!

That reminds me, I asked you a question in a previous post in this thread, but you must have missed it, as you never gave us a reply -

"By the way, that heat sink/sensor pic in the thermal-based meter you linked to is an excellent example of the kind of quality DIY head I was talking about!  [highlight]What make/model thermopile device is that using?[/highlight]"

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Here is the pic I was referring to -
http://www.bauer-electron.com/ebypics/dlb01.jpg

Thanks!

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I guess I missed that question.... I have a Personal life and Business to take care of besides
checking the forum when I get a chance..
When I see a lengthy post... I just skim over it.... I don't read every word... sorry.. :'(

Again... I think the members here would like to see this Advanced Thermopile Technology... you
keep referring to.., :-/

If you are willing to share J.BAUER Electronics LaserBee I research and development costs we will
be more than happy to share our Schematics, Parts Lists, PCB Gerberfiles, Source Code and
Thermopile Technology... with you...

Jerry

Seoguy, you seem to have everything figured out. Coherent, Newport, Ophir and all these companies have just been rooking professionals and hobbiests alike with their overpriced technology that any chump on a laser hobbiest board could replicate.

But talk and optimism is cheap. So, why don't you put your money where your mouth is and bring about this grand DIY revolution in laser power meters. After all, according to your calculations, they should be cheap, easy to manufacture, calibrate, and distribute. I'm sure you'll get rich doing it, but maybe those laser-meter companies will send their shaven gorillas to prevent you from exposing their ruse.

Oh well, at least it got me tinkering a bit with the thermal diode sensor and PIC. Measuring such low voltage (differences) with 10 bit resolution has its noise problems, but it seems feasible at this point.

Too bad i paid little attention in math class.. now i can get temperature readings at fixed intervals as a series, but how to caclulate the asymptote from a couple of such readings has slipped away entirely. If someone has any idea, chime in.. might become something good

For anyone interested to help: see attached picture* - how do you determine the endpoint of the series is 9 volts if you have only the first 3 or 4 datapoints? It's quite easy to eyeball, but i need the maths... and i don't know how the sampling interval relates to RC time at all.

* this is a capacitor charging from a resistor. The curve of warming something up with a laser is very similar.

http://en.wikipedia.org/wiki/Nonlinear_regression
From the page:

Looks similar to what you want.

You could also try to transform the datapoints into linear space by, for example, taking the nth root of every x coordinate and then performing linear extrapolation.

I have high expectations of this meter, with careful construction I can see it working very well.  My current diode can measure power levels as low as 2-3mW and I left the black anodized aluminum rather thick. I have some PICs laying around and a book on assembly so I am tempted to put together a better sensor and see what I can do. Not looking forward to complex math in assembly though.

Well, i develop things in mirkoC, since i can't stand assemby (its for machines, not for humans). But i still need some method to take 3 or 4 of these measurements and get the endpoint from that - within the very limited powers of a pic processor.

Using uC's is a bit problematic for me sometimes as i'm a rather spoiled web developer for a living, getting all the nice builtin php stuff to do the work