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ARGMeter the Open Source Laser Power Meter

ARG

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I unfortunately can't make the whole thing through hole as some components only come in the SMD form factor.

The gain is set by two 0402 resistors. You calculate the gain needed by taking a laser of a known power, shining it on the sensor and reading the voltage.
Say you get a reading of 150mV from a 1W laser on the sensor

1000mV/150mV = 6.6x gain.
The Rg value is always 1k, so from the equation
Gain = Rf/Rg + 1
6.6 = Rf/1k + 1
Rf = 5.6 * 1k
Rf = 5.6k Ohms

I sell these for 150$ with the sensor, if you don't need the sensor or calibration I can offer it to you at 120$, but I will need the gain that you want set.
 



unrealistic

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I sell these for 150$ with the sensor, if you don't need the sensor or calibration I can offer it to you at 120$, but I will need the gain that you want set.
Good price so it comes ready to use? and i learned that formula too =D. You dont sell blank pcb? and why cant use trim pot, I thought resistor have few% tolerance? that might screw the readings
 
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ARG

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The OPA gain is only approximate to get the voltage to where it needs to be to be read by the ADC, the rest of the calibration is done in firmware.

I didn't like the idea of having a trimpot for the gain, resistors will stay at the value they need to be, I didn't want anyone changing the calibration thinking it's the screen contrast :p

I don't sell the blank PCB at the moment as I am out, and working on some updates before getting more fabricated.
I can send you the .brd file if you want to get your own fabricated. :)
 

unrealistic

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Tell me your price for a blank pcb, i will consider if scientech head with this or totally yours depend on price =D send me the file too, interested to see
 
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ARG

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10$ for the blank ARGMeter PCB, shipping is 5$ anywhere in the world. Beware though - there are SOT-23's to solder.

I don't have any more of the v1.1.0 PCB left for sale. You'll have to wait until v1.1.1, I'm doing a bit of prototyping before the next release. I have to wait on a part from China and test out the specs to make sure it will work as intended, then I can release.
 

ARG

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PCB takes four weeks from when I submit it to when I receive it(I would ship DHL but they stole 50$ from me) parts will arrive in two weeks or so.
A couple months?
 
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Atomicrox

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Hey ARG, I just received a MAX1044 on the mail and hooked it up just like the ARGMeter 1.1 schematics. My Ophir hasn't arrived yet, so I tested the negative supply without load.

I get a voltage drop of about 40mV to 80mV on the negative supply relative to the battery and it also fluctuates much more than the batt itself. I've read that even a mV unbalance can affect readings and now I'm worried either my chip is busted or the MAX1044 isn't suitable to this task...

Your chips have this drop as well? Did you compore with another LPM to see if it knocks readings off?
 

ARG

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It should only drop about 30mV-60mV under load (of an Ophir head) The readings won't be effected unless the difference is greater than 100mV, and even then it won't be by a large percentage. You can add a couple 7806 7906 regulators with decoupling capacitors to the design if you want.
I've spoken to a few people about this, with 9V batteries a difference of 60-80mV did not affect their readings. My readings at 1.8W stay within 1mW up to a 120mV rail difference.

This has been changed in the next design, there is a 5V to +/-12V converter with 6V regulators to curb the difference.
VBSD1-S5-S12-SIP CUI Inc | 102-1361-ND | DigiKey
I was also looking at the MAX680 but that may not be able to handle the current demands.
http://www.digikey.ca/product-detail/en/MAX680CPA+/MAX680CPA+-ND
 
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Atomicrox

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I'll take the readings again when the Ophir arrives and let it be if it's < 100mV. Not really sure adding regulators would help since their tolerance is at least 2% (180mV @ 9V). Maybe we could use adjustable regulators and those multi-turn pots to set them at exactly the same voltage...

Do you think the whole thing'll be able to run off USB with that? That would be really cool!
 

ARG

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Yup, the plan to to get it running all of of 5V :)

Adjustable regulators with resistors would work out well, that might be the simplest option at the moment.
What I had in mind now is to use two 8.192V shunt regulators since they have high precision.

I'm also considering the OP amp route, or using a 5V to 12V converter and then a rail splitter.

Lots of testing and prototyping to be done :p The next release will be much better.
I want to make this easier to read and understand so I'm starting fresh and redoing most of it for the next version. Right now my designs are rather poorly presented so I am reworking all of it.
 
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Atomicrox

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Sounds good but I'll wait for your tests before trying any of those, since I don't have another calibrated LPM to test against :p
 

ARG

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I really like the adjustable voltage regulator idea :p I think I'll try that out. Even if someone's multi-meter is off it won't matter as long as both the rails match.
 

ARG

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Update to the ARGraph's! Now introducing v3:


I got a lot of requests to make something smaller, so now this is only 15x31x31mm! It will fit in every LPM!

The part cost has also been reduced from ~55$ to ~20$ that's a 35$ drop in parts :D

Optional status LED's have also been added to the PCB, one for power and one that blinks when data is sent to the data logging application.

Changelog:
* Removed Arduino for standalone a Atmega32U4
* 31mmx31mm size
* Easier to mount
* Entirely USB powered (No external power needed)
* Easier to set up
* 20$ part cost
* More accurate
* Added status LED's (Power & Serial communication)
 
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Atomicrox

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ARG, hope you don't mind me asking for some help here.

Got my Ophir head in the mail today, and your ArgGraph had arrived yesterday. Before testing with datalogging I went and mounted the MAX1044 on a breadboard just like in the ARGMeter 1.1 schematics. Tested the Ophir with it and a DMM and it was reading around 12.5mV with no laser, which seemed a bit too much. Then I took readings of the +9V and -9V rails and noticed a voltage drop on the order of 200mV on the negative rail!

The only thing I can think of is that the battery is too old.. it's reading about 8.7V unloaded and 8.5V loaded with the Ophir. Will get a new one laer today.

Any other ideas as to what may be causing this?
 
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