Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

How about a Homemade Laser Power Meter?

Joined
Jun 30, 2008
Messages
286
Points
0
Today i was reading something about laser power meters and I found that they are based on a thermopile sensor, which is a device who gives a proportional voltage to heat power recived.

The rest of the power meter is a device that reads the output voltage and gives the prportional output power in a LCD screen.
That part isn't hard to make, as all we need is a microcontroller (an inexpensive PIC, for example), a reference voltage regulator and some other inexpensive components. no more than $15.
I can program PIC's and a voltage reader + LCD controller is not a difficult program to make.
It can be done in PIC basic which is an extremely easy (but powerful) language. All i need is some information about thermopile sensors, how they work and where to find one. I know that contactless thermometers use them....

If i get one and discover how it works, i'd probably make a "basic" laser power meter with great accuracy. If i succeed and i get something that reads power, i'd send it to someone with a commercial power meter to calibrate and check it.

So please, if you can cntribute in any way with this proyect, with some technical info or theory about thermopiles, post it and let's see if we can make our own homemade cheap LPM. If I can get all I need for this christmas, i'll start the project.
 





Joined
Nov 3, 2008
Messages
12
Points
0
Funny enough I was playing with a small peltier device at the weekend, (cheap on ebay) and you can easily see a change in voltage by looking across the terminals with a multimeter.

As you say it would be very easy to write some code to look at an analogue input, scale it and then display as mw.

As you say, the hardest part is calibration, but should only be a logistics thing, finding someone who can help, or let you borrow a calibrated unit.

Two people have already done this, one is called Laserbee and seems to be a favourite hobby type meter. The other is the Die4thing.

The Laserbee is still for sale, however the Die4thing seems to be sold out and no longer in production.

Look at the pics on the relavent websites and you will see them.

Let us know what you think, I think there is always a good market for a decent (hobby priced) power meter. I for one would be interested.
 

ArRaY

0
Joined
Jul 18, 2008
Messages
281
Points
0
I don´t think that it would be that hard to make one. At least if you do not opt for 0.1 mW resolution..
Would not be expensive either, if you can get the sensor for cheap. I would also be interest to build my own, but currently I am only learning about µCs(AVR).

ArRaY
 
Joined
Jun 30, 2008
Messages
286
Points
0
The idea was to get something under $50, with basic functions only.
But i've checked prices for thermopiles and... OMG....
I've also read that LPM's use low power thermopiles that can only handle up to 10mW, but they use an attenuator to proportionally decrease the amount of power that actually hits the sensor making it able to read up to 1W or so.

So, if i find a cheap source of thermopiles or another accurate way to check laser power without a thermopile, i'll start with the project and see what happens.

but as I am far far away from the US, I'll probably have troubles getting the thermopile....
 

rkcstr

0
Joined
Dec 1, 2007
Messages
1,368
Points
0
Yeah, the electronics are simple. Knimrod and Kenom were making DIY boards and meters a while back, but that was then there were these surplus Coherent PC boards that had a thermopile on them for pretty cheap. But, those aren't available any more. So, the thermopile are the expensive parts because they have to be accurate and consistent for all wavelengths and over their entire power input range.

BTW, the Coherent thermopiles we had I think could take like 10s of watts of power (not just mW), however you need an amplifier to amplify the signal from the thermopile ( around 1mV per 1W) to 1V per 1W.

Also, there are optical sensors, which I think you were talking about the attenuator, but those are dependent on wavelength and may need correction factors for various wavelengths to be accurate.
 
Joined
Sep 20, 2008
Messages
17,622
Points
113
MarioMaster said:
sorry guys but the Kenometers are wayyyyyyyyy long gone

Well... like "electron" said on another thread... you can still get a Kenometer but the Coherent Sensor
head costs a bit more....Over $700.00 I think.... ::)

But if you can get a hold of one of those Coherent heads cheap... the schematics of the amplifier are
still in the threads somewhere... look for DIY LPM:)
 
Joined
Oct 24, 2008
Messages
1,057
Points
48
I'm interested to see how this turns out. A while back I saw some power meters on ebay that you hook a voltage meter to and it's callabrated to read 1mV = 1mW of light. I think it was like $50 and measured up to 150mW. But I doubt it was accurate, and 150mW isn't enough for most of us. :p

Good luck with this. I wanna get into some programming too. As of now all I really do is program in the ti-84; quadratic formula and summation programs and what not. :)
 
Joined
Sep 20, 2008
Messages
17,622
Points
113
Xplorer877 said:
I'm interested to see how this turns out. A while back I saw some power meters on ebay that you hook a voltage meter to and it's callabrated to read 1mV = 1mW of light. I think it was like $50 and measured up to 150mW. But I doubt it was accurate, and 150mW isn't enough for most of us. :p

Good luck with this. I wanna get into some programming too. As of now all I really do is program in the ti-84; quadratic formula and summation programs and what not. :)

http://www.laserpointerforums.com/forums/YaBB.pl?num=1221793787/16#16
 
Joined
Jun 30, 2008
Messages
286
Points
0
at $700 the thermopile head, I understanud why the Laserbee LPM is considered inexpensive.

FOr the thermopile sensor amplifier i'd have to check my analogue electronics notes... but I think it'll be based on a OP AMP.

"Infrared" thermometers (those to measure temperature inside the ears) use thermopiles, but i think they are not coated for visible broadband...

And to make a photodiode (or similar optical sensior) one, i'd need one laser of every color available to implement automatic measure correction for each wavelenght, and the unic lasers i have are red 650 and red 660nm. And with diodes rated at X wavelenght with tolerances of about 10%, the meter would have low accuracy... and that's not what i want.

I want something basic but accurate, and of course inexpensive, so every hobbyist could have one. But i feel i'm asking for something utopic...
 
Joined
Aug 20, 2008
Messages
709
Points
0
Perhaps you should look into using a peltier module in reverse? Thermopile sensors made for LPMs cost too much to make a DIY meter viable.
 
Joined
Oct 26, 2007
Messages
5,438
Points
83
You also forget that to make a homemade meter useful, no matter the input source (thermopiles, sensors, TECs, etc.) you need to be able to calibrate it against a known source.
 
Joined
Jun 30, 2008
Messages
286
Points
0
Bionic-Badger said:
You also forget that to make a homemade meter useful, no matter the input source (thermopiles, sensors, TECs, etc.)  you need to be able to calibrate it against a known source.

Read carefully the first post ;)
 
Joined
Sep 20, 2008
Messages
17,622
Points
113
Bionic-Badger said:
You also forget that to make a homemade meter useful, no matter the input source (thermopiles, sensors, TECs, etc.)  you need to be able to calibrate it against a known source.

Hey BB...

you are absolutely correct... without a calibrated LPM... it is difficult to do...
"erdabyz" can always send it to us for testing... once his LPM project is finished....
We have invested over $3000.00 in equipment to be able to properly calibrate the LaserBee I. ;)

Jerry
 

Benm

0
Joined
Aug 16, 2007
Messages
7,896
Points
113
erdabyz said:
And to make a photodiode (or similar optical sensior) one, i'd need one laser of every color available to implement automatic measure correction for each  wavelenght, and the unic lasers i have are red 650 and red 660nm. And with diodes rated at X wavelenght with tolerances of about 10%, the meter would have low accuracy... and that's not what i want.

I want something basic but accurate, and of course inexpensive, so every hobbyist could have one. But i feel i'm asking for something utopic...

Well, 10% accurate isn't even that bad, at least it allows good relative comparisons between lasers. I seriously doubt that $50 in parts will get you 10% accuracy over a decent power range, even if it would require calibration for each wavelength.

I have seen some homemade designs that are based on thermal sensing though, with the sensor being little more than a black disc glued onto a plain diode used as a sensor. This gains you wavelength independence, but given the thermal capaciy of the disc/diode system, it will respond very slowly and with limit accuracy too. Also, sensitivity is not that good, but perhaps that isn't even a big problem since most LPF users would be interested in perhaps a 10 to 1000 mW range, and have no need for expensive uW-measuring thermopiles.
 




Top