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Old 01-25-2010, 09:55 PM #17
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Default Re: Very simple DIY laser power meter with thermistor

I've heard of this way of measuring laser power. Did it say to file down flat the rounded part of the LED? the result from this can vary greatly from one green LED to the next. The curvature of the round front, space between the die and the round front, all of these affect the amount of laser hitting the LED die. Dies can differ. Unless you have a reference laser (School lab or work) or a buddy with an LPM, you won't know how close you are to the truth.


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Old 09-26-2012, 08:53 PM #18
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Default Re: Very simple DIY laser power meter with thermistor

So I know this is a very old thread, but after hours and hours of searching, this is the first DIY meter that I think has a chance of being calibrated without using an already calibrated system. While the DIY meters we have here are great, they all require a known source or a calibrated comparison. I like that this method uses the heat output by a resistor to calibrate itself.

Before I journey down a fruitless path, has anyone tried this before? Is there a post detailing the results? I notice that some of the discussion above deviated from the original idea of dialing down the resistor output and measuring the difference in power to maintain a single resistance from the thermistor.
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Old 09-27-2012, 12:05 PM #19
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Default Re: Very simple DIY laser power meter with thermistor

Quote:
Originally Posted by TrailBlazer84562 View Post
So I know this is a very old thread, but after hours and hours of searching, this is the first DIY meter that I think has a chance of being calibrated without using an already calibrated system. While the DIY meters we have here are great, they all require a known source or a calibrated comparison. I like that this method uses the heat output by a resistor to calibrate itself.

Before I journey down a fruitless path, has anyone tried this before? Is there a post detailing the results? I notice that some of the discussion above deviated from the original idea of dialing down the resistor output and measuring the difference in power to maintain a single resistance from the thermistor.
Hmmm...

Once you try this calibration idea be sure to let us know how
easy it is to precisely calibrate your LPM... I'm curious about this
one... Good luck with your project.


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Last edited by lasersbee; 09-27-2012 at 12:05 PM.
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Old 09-27-2012, 05:43 PM #20
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Default Re: Very simple DIY laser power meter with thermistor

What about using a piece of pyrolytic graphite as the sense surface?
This is near 100% absorptive at most wavelengths and is mechanically strong.

Another useful tip,any old broken HP printer pre 2006 has an LM35DZ on the lid sensor PCB.
This is good to 0.1 Celsius accuracy once calibrated, and repeatable.

Its also useful to compare readings between a simple cheap 1n4148 and the sensor being tested,
those are about 10mV per Celsius change.

Kind regards, -A

Last edited by conundrum; 09-27-2012 at 05:45 PM.
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Old 10-02-2012, 07:44 PM #21
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Default Re: Very simple DIY laser power meter with thermistor

Quote:
Originally Posted by conundrum View Post
What about using a piece of pyrolytic graphite as the sense surface?
This is near 100% absorptive at most wavelengths and is mechanically strong.

Another useful tip,any old broken HP printer pre 2006 has an LM35DZ on the lid sensor PCB.
This is good to 0.1 Celsius accuracy once calibrated, and repeatable.

Its also useful to compare readings between a simple cheap 1n4148 and the sensor being tested,
those are about 10mV per Celsius change.

Kind regards, -A
I have a handful of LM35s lyin around, but they take away from the simplicity of this solution. I am trying to find some prolytic graphite as we speak. The first website wanted 100 bucks a unit! Another site is selling 20mmx20mm squares for three bucks, but they want 10 bucks for shipping. I'll have to see if I can find them cheaper. Do they sell them at any brick and mortar shops?
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Old 10-03-2012, 07:16 AM #22
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Default Re: Very simple DIY laser power meter with thermistor

Hi, I have a few bits of PG here from my magnetic and radiation sensing experiments.

PM me your address and I'll send you some along with mounting hardware.

Also, you need to ensure that it is held to the thermistor with something thermally conductive such as low melt alloy or laptop thermal paste.
I've used a mixture of Epoxy and thermal paste before which somewhat worked, better to use the "dry" sort.

Kind regards,

-A

Last edited by conundrum; 10-03-2012 at 07:23 AM.
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