DIY Laser Power Meter

chimo said:

RoSSco, sorry for taking so long to reply - work was crazy this week and I have to head out of town again on Sunday for the week. Can you PM me you paypal info and I will send payment off before I leave? Thanks,

Paul

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PM sent! I see there are now 44 of these available.

I still haven't received mine yet though.

roSSco said:

[quote author=chimo link=1200112201/90#94 date=1201888758]RoSSco, sorry for taking so long to reply - work was crazy this week and I have to head out of town again on Sunday for the week.  Can you PM me you paypal info and I will send payment off before I leave?  Thanks,

Paul

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PM sent!  I see there are now 44 of these available.  

I still haven't received mine yet though.  [/quote]

Paypal sent and a PM with additional info. Thanks!

Paul

My circuit board and sensor came in today! Gotta get busy.

The circuit board looks very nice knimrod.

BTW, if anybody has trouble getting the LTC1050 off the board, or would rather order one, I found an alternative to Digi-key.
At DigiKey it looks like $4-5 for the part, $5 handling, and $7.15 shipping.
At this place it's $4.40 for the part, no handling charge and $4.00 shipping.
http://www.futurlec.com/LinearTechnology/LTC1050.shtml

I hope you guys are taking pictures...

Zarniwoop said:

BTW, if anybody has trouble getting the LTC1050 off the board, or would rather order one, I found an alternative to Digi-key.
At DigiKey it looks like $4-5 for the part, $5 handling, and $7.15 shipping.
At this place it's $4.40 for the part, no handling charge and $4.00 shipping.
http://www.futurlec.com/LinearTechnology/LTC1050.shtml

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Thanks.  That is a better deal.

Regarding getting the LTC1050 off the Coherent board, the easiest way is to use a mini-torch or heat gun to heat the back of the board where the IC is while gently pulling on the IC from the front.  As soon as it's hot enough, the IC will slide right out.

My boards arrived today....

Awesome job on those!!!

Built my first meter..and it works PERFECTLY!!!!!

I have one question....
The Zero Function would seem to require a finer resolution to actually and accurately zero the meter....
can the "Fineness" of the zero be changed??



My resistors measured EXACTLY the same as yours!!!

Must have come from the same batch!!!

Anyway ..I tested a laser that I had a calibrated power graph for over a 60 second timeframe .and this meter tracked almost to the Milliwatt!!!!

Your formula is dead on!!!!


All I need now is for my displays to arrive..and I'm living LARGE!!

Thanks Again Knimrod......

Please keep me in mind when you come up with a PC interface!!

Larry

LarryQ said:

My boards arrived today....

Awesome job on those!!!

Built my first meter..and it works PERFECTLY!!!!!

I have one question....
The Zero Function would seem to require a finer resolution to actually and accurately zero the meter....
can the "Fineness" of the zero be changed??



My resistors measured EXACTLY the same as yours!!!

Must have come from the same batch!!!

Anyway ..I tested a laser that I had a calibrated power graph for over a  60 second timeframe .and this meter tracked almost to the Milliwatt!!!!

Your formula is dead on!!!!


All I need now is for my displays to arrive..and I'm living LARGE!!

Thanks Again Knimrod......

Please keep me in mind when you  come up with a PC interface!!

Larry

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The zero function should give you a zero correction range of +/- 60mW.  Let's make sure it's working properly....  Ground the input to the amp (0 volts) and monitor the voltage output while adjusting the zero offset from one extreme to the other.  It should change from -60 to +60.  This corresponds to the +/- .6 volt forward voltage drop of D1 & D2.  If it's not close to that, something is probably wrong.  Make sure the installed polarity of D1 & D2 is correct.  If either are backward, the voltage will be way too high and the zero will be way too sensitive to be useful.  It will be easier to use the volt scale of your multimeter instead of the mV scale so you're not being distracted by changes of less than 1mV.  

I Like mine the way it is and the sensitivity seems right for me at about .4mW per degree of rotation of the pot.  However, if it's just too sensitive for your taste, you could try increasing the value of R5 or just using a ten-turn pot for the zero offset control.

Congrats on your build!  How 'bout some pics?  

My circuit seems proper.....things check out properly....


I see now after playing around..the problem is not the zero circuit..but the actual sensitivity of the thermal head itself!

if you walk in front of the meter..it picks up your body heat!

I'm trying to compensate the zero for 1-4 mV on the meter..and it's tough..even air currents from my ceiling fan affect this meter....

though as I say..I'm trying to zero out 000 and dancing with 002.....004..-001...ect..ect....

I have to say..this head is sensitive...and accurate!!!

THis IS a COHERENT power meter....all the magic is in the head....lest anyone doubt...

If we could find a way to power the remainder of the board that the head comes attached to..we could have heater...thermal regulation...

I'm going to build at least two of these....Maybe three..if my parts stash holds up!!!




Larry

I don't think the heater would help that much.  Probably the best thing would be to improvise a shielding tube on the front of the meter to block off-axis radiation to the sensing surface.   I'm pretty sure the heater control thing was to stabilize the sensor because it was in a an enclosed, confined area where it could not give up any heat it accumulated or absorbed very well.  I think that accumulated heat would cause drift.  The heater would allow for a controlled and stable heat offset in the enclosed space.  I'm not sure about all that but it's probably only an issue with higher power lasers.

The meters are indeed sensitive..  I can even measure my cheap dollar store laser pointers at 1-5mW repeatably.

The off-axis sensitivity is not unique to this meter.. It's fairly common for all thermopile meters.  My old Coherent 210 thermal head has an optional 2" long aluminum tube that screws into the front of the head.  Having a digital display makes it seem worse but the old analog meter of the 210 shows the same sensitivity issues. It's just not as obvious.

I got it working! I had hoped my MXDL would be putting out more, but I'm sure it needs batteries.

I came up with a cool way to connect to PS to the circuit board and will share pics tomorrow. I'm dead beat now.

I got 50mW peak from my KD copper, 190mW from the Dorcy and 260mW from the MXDL (w/weak batteries).

All that's left is to drill some holes in the project box and mount it all up.

The instructions posted here were easy to follow. I discovered on my own that the circuit on the back side of the PS can be removed. I had to because the project box I used was only 2" deep.

See ya all tomorrow.

By "off axis" do you mean that the laser needs to meet the PS head on and not at an angle? I ask because most of my measurements were made with one hand while holding the DMM connectors to the pcb as I tested it. If so I should be able to get a little more power out (measured) of my lasers.

roSSco said:

By "off axis" do you mean that the laser needs to meet the PS head on and not at an angle?  I ask because most of my measurements were made with one hand while holding the DMM connectors to the pcb as I tested it.  If so I should be able to get a little more power out (measured) of my lasers.  

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No.. The laser can hit the sensor from just about any reasonable angle and should still be measured accurately.

roSSco said:

[quote author=knimrod link=1200112201/15#19 date=1200665971]If those of you outside the US really want one, I'm sure we can figure out how to get it to you.

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I'll buy some for those that need it overseas. It's not an illegal to export item is it? :

Paypal me the funds for the item + shipping and I'll be happy to help.

r0ssc0i@yahoo.com[/quote]

Hey r0ssc0,

I would like to take you up on that offer, how can I find out the postage so that I know how much money to send you?

cheers.

knimrod said:

[quote author=roSSco link=1200112201/105#108 date=1202015497]By "off axis" do you mean that the laser needs to meet the PS head on and not at an angle? I ask because most of my measurements were made with one hand while holding the DMM connectors to the pcb as I tested it. If so I should be able to get a little more power out (measured) of my lasers.

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No.. The laser can hit the sensor from just about any reasonable angle and should still be measured accurately. [/quote]
I need batteries!