DIY Laser Power Meter

woop said:

would a tec thermopile be useful for measuring laser power?
maybe if i put it on a heatsink and paint one side matte black.
I know it would be uncalibrated but would it work and be consistant

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I see you had the same idea as me... I started a thread on it and tried it yesturday.

I wasn't happy with the results, which is why i'm here now...


A peltier is very sensitive, and creates a voltage, relative to the power of the laser.. It would have to be multiplied of course, but unfortunatelly, it is VERY slow...

It takes a while, till it climbs to the highest voltage a laser can produce, and the higher it goes, the slower it becomes.. Also, it wouldn't absorb all wavelengths the same, so it would be similiar to a solar cell, only slower....

amkdeath said:

considering im running the open can at 430mA, according to DR. Lava's various plots i should be getting WAY over 160mW... although, I am using unprotected 3v CR123's, maybe when my 3.6v CR123's come from DX it will be better

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Well, there's your problem.. You're feeding the 317 driver only two 3V batteries.. The LM317 needs MORE than 6V to regulate the current successfully.
This means, you have to choose batteries, that are going to have 6V when empty, and much more, when full..

When you get the 3.6V, they will give you 8.4V when full and 6V when empty, and your laser power will be constant over this entire voltage range..

But when you only give it 6V, and pull a high current, the batterys drop in voltage immediatelly. As the voltage drops, the open can is only getting what the batteries are giving out minus 3V, which means it is very underpowered.... The emptier they get, the less current flows through your laser, and the regulation doesn't work anymore at all..


If you were to measure the current, you would notice, that it's not anywhere near to what you think you set it..

Many people made the same mistake, because when they read the 317 needs 6V, they give it batteries that add up to that exactly.. But if you give it more, the output would stay constant up to 37V input (with lots more heat in this case - needs heatsinking but works)...



So yes, when you get the DX 3.6V batteries, your lasers will finally get the current you thought you were feeding them and work better...


Let me know about the measurements, once put in proper batteries... I'm also waiting for DX batteries and i just got an open can. I'm also building a tiny peltier cooling system for it, so i can get the power of a labby in a portable.


On the other hand, i fear, that once i build the DIY LPM, i will find out, that my 16x lasers are putting out less than i thought as well..

well, I finally took the time t o read this topic.. and just ordered my sensor. I'll be making my ownpcboard with surface-mount components.

But I wanted to point out this eBay seller where I have previously bought dpm's - I have 4-1/2 digit ones, they work fine common-ground.

DanQ

danq said:

well, I finally took the time t o read this topic.. and just ordered my sensor. I'll be making my ownpcboard with surface-mount components.

But I wanted to point out this eBay seller where I have previously bought dpm's - I have 4-1/2 digit ones, they work fine common-ground.

DanQ

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I just purchased one of the blue ones from that seller the other day. Looks nice, 2V range, common-ground, accurate to the 10th of a mV and decimal point is movable. So, I should be able to set it to show from 0.1mW up to 1999.9 mW with the sensor I purchased too

Could someone please post more detail pictures as how every thing is connected internally? [smiley=dankk2.gif]

knimrod said:

[quote author=amkdeath link=1200112201/120#124 date=1202073200]or mabe someone can post a clear close up of the front and back of the finished and soldered GB board... im still confused how the coherent sensor attaches to the board

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Maybe this picture will help. The connector in the upper left corner connects to the sensor head with the supplied cable.


[/quote]




*gasp* the monk is that you asking that question!!?

Looks like i'll be building one of these as well.. Thanks to roSSco i can get the thermopile, even tho i'm on the other side of the planet..


Now i just need to decide between an LCD or a LED display.


Can't wait to start measuring my lasers.. Even tho i fear they will show less power, than i imagined..

IgorT said:

Can't wait to start measuring my lasers.. Even tho i fear they will show less power, than i imagined..

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well, the positive side of that is that if you're impressed with their current power, just think how amazing they'll be when you get 'em up to where you thought they were...

amkdeath said:

*gasp* the monk is that you asking that question!!?

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how do you connect the DPM to the power switch and amp board?

danq said:

well, the positive side of that is that if you're impressed with their current power, just think how amazing they'll be when you get 'em up to where you thought they were...

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You are right.. I will be able to compare them to the known diodes, to see if they're the same, and know what i can expect from them...
I have three 16x, two of them from Samsung and one from an old NEC.. I think the Samsungs might even be the same as the good batch of Sony LDs. The NEC on the other hand was weird.. It didn't want to stay in the AixiZ module, it was too small.. Had to solder it in.

All of them are very powerfull (the Samsungs a little more i think), but once i also know the real power, i will be able to find the best current for them.


Besides, i now have acces to open cans, which will be able to go much further, than what i was hoping, the old ones are putting out...



Oh, danq.. I finished the SEPIC driver, and it works perfectly! I finally have current regulation from only two Ni-MHs or one Li-Po.. I'm definatelly gonna use this driver for the open can, so it can be small yet very powerfull..

TheMonk said:

how do you connect the DPM to the power switch and amp board?

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Easiest way it to tap +9V from the power switch (switched side) and run that to the DPM Power.  Power Ground for the DPM is any ground.  You can just wire the Amp signal outputs to the DPM signal inputs.  

Well, I have almost all the parts now. Just waiting on the mail for the cct board.

After de-soldering the op amp, I cleaned off the rest of the components. I used a heat gun - works great for mass desoldering. Upside down, apply heat and tap the board - the components fall right off for the most part.

I am debating how I want to configure my enclosure.

I see that most people have the DPM and the sensor opening on the same face. Does that make it hard to read the panel when a high powered laser is shining on the sensor?

I am considering opposite sides for the sensor and DPM or putting the sensor on the front and the DPM on the top. I would have liked to put the sensor on the small side and the DMP on the front, but my box is not deep enough.

BTW, has anyone else who purchased a DPM checked it for accuracy? Mine came in the mail today (NewPower 2V/200V). I checked it against my multimeters and I was getting about a 25mV difference (DPM was high). There's a trimmer pot on my module that allowed me to zero it in to the same readings as my DMMs.

Paul

chimo said:

I am considering opposite sides for the sensor and DPM or putting the sensor on the front and the DPM on the top.

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I'd think opposite sides would not be good - do you want your eyes facing the laser?

If you're wearing goggles and the dpm is a contrasting color you're set in terms of visibility... maybe should have both red and blue dpm's?

danq said:

[quote author=chimo link=1200112201/315#315 date=1204602625]
I am considering opposite sides for the sensor and DPM or putting the sensor on the front and the DPM on the top.

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I'd think opposite sides would not be good - do you want your eyes facing the laser?
[/quote]

Very good point. Looks like front/top, front/front or front/external_side.

I hook up the DPM pin 1&2 to a 9v battery to power up; and connect pin 3&4 to measure a 1.2v battery. After I disconeted pin 3&4 the meter still shown 1300 and every second it will drop a few millivolts. I can zero out the meter display by shorting pin 3&4, is this normal for this DPM? :-/

BTW dip switch 1,2,3 & 5 are off 4 on.

TheMonk said:

I hook up the DPM pin 1&2 to a 9v battery to power up; and connect pin 3&4 to measure a 1.2v battery. After I disconeted pin 3&4 the meter still shown 1300 and every second it will drop a few millivolts. I can zero out the meter display by shorting pin 3&4, is this normal for this DPM? :-/

BTW dip switch 1,2,3 & 5 are off 4 on.

Click to expand...

thats how I have my dip switches. there si a post somewhere in here, I believe page 6 which says all about hooking up the DPM