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ArcticMyst Security by Avery

My DIY Laser Power Meter ***PIC HEAVY***

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Feb 9, 2011
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My DIY Laser Power Meter

I want to introduce you guys to my recent build. I have been working on this off and on for a few months now. The circuit is based off MarioMaster from his thread with all the parts and components needed listed there: http://laserpointerforums.com/f42/diy-thermal-lpm-under-50-a-51129.html

This is actually my second attempt at this since my first one didn't work so well. My first attempt failed because of an improper connection made on the second (unused) op-amp on the LM358.

I first had the unused op-amp with one input to GND and the output feed back into the other input like this:
opampwrong.jpg


That didn't work and actually made the IC extremely hot and readings fluctuated erratically. I gave up after that failed try, but after a month or so the topic came up and a few members helped me out. It seems that a dual op-amp IC like the LM358 won't work correctly since both op-amps feed from the same power supply, but would work with a single op-amp IC.

So after some revision here is the final schematic:
LPMschem.jpg


Final board:
*not all connections are seen because they are connected to the ground plane*
LPMbrd-1.jpg


Acutal board (front):
IMG_0221.jpg


Actual board (back):
IMG_0222.jpg


Board all components soldered:
IMG_0224.jpg


IMG_0225.jpg


8x8 mm TEC:
IMG_0098.jpg


8x8 mm TEC (uncoated):
IMG_0099.jpg


8x8 mm TEC (coated):
IMG_0101.jpg


Paint used (Rust-O-Leum high heat flat black):
*It's important to use a non glossy paint most of the beam is absorbed*
IMG_0097.jpg


Heatsink used:
Digi-Key - EA-T220-64E-ND (Manufacturer - EA-T220-64E)
IMG_0109.jpg


Heatsink with TEC thermal pasted on:
IMG_0234.jpg


Heatsink with 1/8 plug cable attached:
IMG_0231.jpg


Project box (6x2.5x2):
*taped up and ready to be cut :yh:*
IMG_0223.jpg


Project box cut with volt panel meter unassembled:
IMG_0226.jpg


3 1/2 digit volt panel meter:
UP8135A-R20V-2.jpg


Switch being mounted:
*I used a DPST (double pole single throw) switch to connect both the volt panel meter and amplifier circuit*
IMG_0227.jpg


Inside box:
IMG_0228.jpg


1/8 plug jack:
IMG_0229.jpg


Mounted switch:
IMG_0230.jpg


Completed LPM (off):
IMG_0235.jpg


Completed LPM (on):
*Ignore LPM output value because it's not calibrated yet*
IMG_0237.jpg


Videos:

Off/on:


Sample metering:


Final thoughts:
Overall I'm pleased with the outcome. However, there are just a few things that bothered me. It will do for the time being until I buy a credible LPM. I think I spent about 60-80 dollars total for this build.

1. When I attempted to zero my meter it will not go to zero! It will only set at -.011V. :mad: I tried using my multimeter and it zeros fine. So it might be the panel meter having the problem.

2. When I try to calibrate for the power output it does not want to go down lower than .194V because I know for sure my PHR-803T isn't outputting over 200mW, unless its a freak diode. I highly doubt it because I tried metering my 445nm and it wont go down less than 2W. :(

3. I accidentally nicked the front of my LPM box with my dremel as I cut the hole for the panel meter. Not a big deal, but I like my things spotless :(

:thanks: for looking!

Any questions, comments, concerns feel free to post.
 
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Re: MY DIY Laser Power Meter ***PIC HEAVY***

Very well done!!
I love to see the nicely done build tutorial as well. Thanks for sharing, i'll have to add this to my project list. :beer:
 
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Re: MY DIY Laser Power Meter ***PIC HEAVY***

Nice clean DIY build....:gj:
I like that that you use Masking tape to mark
and cut the holes... A professional trait..;)

I've seen badly built/cut enclosures from sellers
that would make you cringe...

Nice solid and neat wiring...
Good choice of an 8mm X 8mm TEC... much faster
response than the 15mm X 15mm type..


Jerry
 
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Re: MY DIY Laser Power Meter ***PIC HEAVY***

Nice clean DIY build....:gj:
I like that that you use Masking tape to mark
and cut the holes... A professional trait..;)

I've seen badly built/cut enclosures from sellers
that would make you cringe...

Nice solid and neat wiring...
Good choice of an 8mm X 8mm TEC... much faster
response than the 15mm X 15mm type..


Jerry

Like my first and second attempts at mounting that laserbee? :tinfoil: haha

-Dustin
 
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Re: MY DIY Laser Power Meter ***PIC HEAVY***

No Dustin...
I'm referring to multiple products being sold as "well" built
business products...

Any member willing to do a DIY build will get kudos from me
just for trying... No matter what the outcome looks like... ;)

Jerry
 
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Re: MY DIY Laser Power Meter ***PIC HEAVY***

No Dustin...
I'm referring to multiple products being sold as "well" built
business products...

Any member willing to do a DIY build will get kudos from me
just for tying... No matter what the outcome looks like... ;)

Jerry

haha, must admit my first two attempts turned out as... well flat out horrible :p
I still have it in the 3rd clear enclosure and its living happily :)

@OP sorry for threadjack, very nice work! nice and clean :wave:

-Dustin
 
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Re: MY DIY Laser Power Meter ***PIC HEAVY***

Very well done!!
I love to see the nicely done build tutorial as well. Thanks for sharing, i'll have to add this to my project list. :beer:

Thanks 532 with Envy! :beer:
Nice clean DIY build....:gj:
I like that that you use Masking tape to mark
and cut the holes... A professional trait..;)

I've seen badly built/cut enclosures from sellers
that would make you cringe...

Nice solid and neat wiring...
Good choice of an 8mm X 8mm TEC... much faster
response than the 15mm X 15mm type..


Jerry

Thanks Jerry! I was thinking of ways on how to cut it and I thought just making lines would have been hard to follow through. So I had some painter's tape and it really helped me guide my dremel in making some nice clean cuts.

As for the TEC, I'm amazed at how sensitive it is. I tried to put my finger in front of it and the meter went up 2-4mV.

haha, must admit my first two attempts turned out as... well flat out horrible :p
I still have it in the 3rd clear enclosure and its living happily :)

@OP sorry for threadjack, very nice work! nice and clean :wave:

-Dustin

Thanks man! Don't worry about it :)
 
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Great job with your documentation there. I like how you listed your parts and supplies and links. Very nice ;) Which TEC did you go with? I see you sacrificed getting a 4 digit display in order to get a display that has input isolation. I'm torn between which to get.

When I attempted to zero my meter it will not go to zero! It will only set at -.011V. I tried using my multimeter and it zeros fine. So it might be the panel meter having the problem.

Multimeters are generally bad at reading very low negative voltages.

The issue is the op amp has a 7mV offset I think? So your offset compensation measures are likely an overkill? What happens if you bypass your your compensation and just tie X2-2 to X2-4. If it still reads negative at that point, you can safely confirm its an issue with the lcd meter screen. Theres the pot on the meter though that should fix this problem.

Eitherway, beeatiful project! =)
 
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Thanks random person!

The TEC I used was an 8x8 mm module, I forgot the exact model number but it should be in that picture on the first post.

And actually I purchased the 3 1/2 digit on purpose for its compact size and doesn't compromise the output reading since it can display digits 0-1.999V or 0-19.99V. The half digit can only display 0 or 1. It also has a dip switch on the back with allows for common and or isolated ground so that was a plus.

The actual IC I used was a Fairchild Semiconductor LM358N. Input offset voltage typical is 2.9mA and max at 7mA. I didn't think that would have mattered much since other members who have built this same circuit had no zeroing issue. You could be right about the pot on the panel meter. The datasheet for that was pretty vague. I'll try adjusting that and see what happens.
 
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With that Alpha circuit by MM... We have found that the Zeroing control
starts to become an issue after multiple High Power Laser tests and
the heat from thesurface of the sensor gradually propagates to the
heat sink and theheat sink starts to warm up above ambient temperature.

At that point if the Zeroing pot can no longer Zero the reading... the solution
(with the circuit as is) is to let sensor/Heat Sink acclimate to the Ambient test
area temperature... (~30min to ~1hour) before doing another test...


Jerry
 
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Benm

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Looks like a very nice build to me :)

Where did you get that TEC?

Also, i wonder if it is possible to do thermal calibration on these units: You could temporarely fix a SMD resistor to the sensor surface (using removable thermal compound), and then apply a known amount of power (say 200 mW).

I think the prescense of the smd heater resistor will have some effect on the value read, but perhaps this effect is small enough to make an acceptable 5%-ish calibration without a laser of known power?
 

Benm

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What is the advantange of that TEC over this one? 00711-5L31-03CA

The price difference is pretty big, and so is the difference in rated power - but is that important in this application?
 
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What is the advantange of that TEC over this one? 00711-5L31-03CA

The price difference is pretty big, and so is the difference in rated power - but is that important in this application?

His TEC Tmax is 200C and the one you linked is only 125C...
That is only important if you decide to bake it...

Your TEC link is cheaper at ~$14.00 and the OP's TEC is ~$39.00
I would assume the OP's TEC uses more P/N Thermocouples..
hence (probably) the price difference... IMO

I cant see why either TEC would not work as Thermopiles with
that DIY Op Amp circuit...


Jerry
 
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@ Benm

Also, the other differences and the main reasons that yours is more cheaper, they are.

The one you say is smaller 8 x 8 x 3.6 mm, the other is 8.4 x 8.4 x 2.3mm

Yours has a much lower number of Couples, only 7 couples (14 pellets, 7 N and 7 P), and this of Jufran88 has 31 Couples (62 pellets, 31 N and 31 P)

Apart from this, the voltage, amperage and temperature, which are also different in the 2 models, and this can be seen easily in the datasheets.
 
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Sorry, got a question for you since i'm very new to PCB design.

When looking at
LPMbrd-1.jpg


Apart from the VIAs and the 2 red traces, is that really all the copper you have on the top side of your board? Is there still copper everywhere else on the top layer that is simply not connected to your traces?

Also, isn't it best to make use of copper plates as much as possible? I would assume just using traces would cause more noise? Especially regarding power and ground. When looking at PCB design files on this site generally all I see are just traces and not plates... why is that?

Anyone else care to chime in when its best to use a copper plate versus a trace?
 
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