DIY Thermal LPM for under $50

Sorry bros, that took alloonnggg time to create. Didn't work so long on it so someone else could try to sell it for me...that is IF I can sell it... theres still curcial development left that could be deal-breaking for all I know. However, there isn't any cheap and easy magical sensor or mystical coating going on here that i'm just being a dick for not sharing. This again was the product of many hours of engineering work. Its a multi-processor spi-biwire design and SMT only design. Anyone who could make heads or tails of the code / schematic would be able to build their own LPM of equivalent magnitude without having to reference mine.

The idea is simple and introduced in this thread, you need to measure the voltage coming from the peltier very accuartely. In addition, you need to filter,buffer,amplify, and bias that voltage. From there, its just a matter of being able to write low level driver code for LCD and USB implementations / communications as well as having access to high end meters for calibration.

random person said:

Sorry bros, that took alloonnggg time to create. Didn't work so long on it so someone else could try to sell it for me...that is IF I can sell it... theres still curcial development left that could be deal-breaking for all I know. However, there isn't any cheap and easy magical sensor or mystical coating going on here that i'm just being a dick for not sharing. This again was the product of many hours of engineering work. Its a multi-processor spi-biwire design and SMT only design. Anyone who could make heads or tails of the code / schematic would be able to build their own LPM of equivalent magnitude without having to reference mine.

The idea is simple and introduced in this thread, you need to measure the voltage coming from the peltier very accuartely. In addition, you need to filter,buffer,amplify, and bias that voltage. From there, its just a matter of being able to write low level driver code for LCD and USB implementations / communications as well as having access to high end meters for calibration.

Click to expand...

Still nicely done.
I want to tip you on Fusion PCB Service [PCB08511P] - $9.90 : Seeed Studio Bazaar, Boost ideas, extend the reach as they have a pcb service down to $9.9 for a 50x50 board (you get 10 for the price!).
I used em for my latest quad controller board (for RC stuff) and they were quick too. Boards came out nice.
(Your board looks custom so I assume you may have use for such a service, like I do.)

My LPM still works too btw, made by the same ideas as in this thread.
I used differential ADC though allowing 0-adjustment to be done directly, then the gain is done by the code that interprets/translates the reading to a power value. Simplifies electronics a lot and gives 3 power ranges automatically selected in software. (1x, 10x and 200x gain to support both low and high powered measurements.)

random person said:

My DIY LPM is b0$$ with 16 bit delta-sigma ADC + 24 bit oversampling + 3rd. order hardware input filter/buffer. Fully USB 2.0 compliant + Data logging.

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Is it just me, or is that picture half real and half generated?

I have something very similar in the works.

What would you need with 24 bit resolution?
that would give you microwatt resolution.
You could affect the reading by thinking to hard lol.

KreAture said:

Still nicely done.
I want to tip you on Fusion PCB Service [PCB08511P] - $9.90 : Seeed Studio Bazaar, Boost ideas, extend the reach as they have a pcb service down to $9.9 for a 50x50 board (you get 10 for the price!).
I used em for my latest quad controller board (for RC stuff) and they were quick too. Boards came out nice.
(Your board looks custom so I assume you may have use for such a service, like I do.)

My LPM still works too btw, made by the same ideas as in this thread.
I used differential ADC though allowing 0-adjustment to be done directly, then the gain is done by the code that interprets/translates the reading to a power value. Simplifies electronics a lot and gives 3 power ranges automatically selected in software. (1x, 10x and 200x gain to support both low and high powered measurements.)

Click to expand...

I like the way you think. Yup, Seeed was my fab for this board. Seeed is awesome and the only PCB fab I go with these days. Wasn't a huge fan of dorkbotpcb or batchpcb.

As for what your referencing, yea, I'm using a micro with a 16bit adc. So I have 2 micros, 1 is a master and the other is an adc micro slave. Originally I planned to use the micros internal PGA (programmable gain amplifier) to support multi power modes but the pga on the micro appeared to have some non linear elements when referenced with a true professional meter. Consequently I ditched that and went with a uni-polar design based upon a highly filtered/gained input.

However, if I run into a case where i'm maxing out my ADC at ~2-3W, I may lower my external input gain and rely on PGA gains and a more careful calibration. ... my specialty is hardware as opposed to software which is why i'd sooner have an external filter then have to mess around in software. Software is a necessary abomination that should be used as little as possible :evil:

Is it just me, or is that picture half real and half generated?

Click to expand...

That would be cool if I had nice CG skills in addition to my electronics skills =) . No CG here but I did use photoshop to sharpen the image. In addition the screen looks abit odd since their is plastic on it?

random person said:

I like the way you think. Yup, Seeed was my fab for this board. Seeed is awesome and the only PCB fab I go with these days. Wasn't a huge fan of dorkbotpcb or batchpcb.

As for what your referencing, yea, I'm using a micro with a 16bit adc. So I have 2 micros, 1 is a master and the other is an adc micro slave. Originally I planned to use the micros internal PGA (programmable gain amplifier) to support multi power modes but the pga on the micro appeared to have some non linear elements when referenced with a true professional meter. Consequently I ditched that and went with a uni-polar design based upon a highly filtered/gained input.

However, if I run into a case where i'm maxing out my ADC at ~2-3W, I may lower my external input gain and rely on PGA gains and a more careful calibration. ... my specialty is hardware as opposed to software which is why i'd sooner have an external filter then have to mess around in software. Software is a necessary abomination that should be used as little as possible :evil:

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Hehe. I do both SW and HW.
My current RC project puts a quad controller (for 4-motor helicopter) with 4 direct motor controllers, 3 axis gyro, 3 axis accellerometer, 3 axis magnetometer, 2.4 GHz radio and barometric height sensor on a single 16x16mm 1g pcb (including components) and the firmware is compatible with existing radio transmitters as I reverse engineered the protocol. The controller is for nano scale quad's but can control large ones too using external motor controllers for the larger motors.

The LPM can be calibrated accross the entire range via multiple points and interpolation/curve fitting btw. Also, the nonlinearity in many amps is a lot smaller than the errors you get from simply a draft in the room.

I have found this thread recently, as I was searching for a cheapo lpm, after building my first 445nm laser.
What I found is that I had to reverse the legs of the 10k trimmer for correct function (to raise the mV to reference laser mW, instead of lowering it).

Otherwise, the circuit works well. I did not have an LM358 so I used an LM324 instead and modified the circuit, accordingly. The peltier used is a 40mmx40mm TEC1-12705, painted with one layer of black paint then a layer of heat-resistant matte black.

The reading is slow, around half-one minute and the beam is defocused so it covers the whole area of the TEC.
I guess it is better to wait longer for the reading with defocused beam than to use a very small TEC and burn it with a focused beam of 1-2W :thinking:
Plus, it is much more safe to measure the defocused beam, in case of unwanted reflection if the laser moves accidentally or such.

My reference 660nm dilda outputs 190-200mW so I set the lpm to 200mV and measure my 445nm diy laser. It showed around 1000mW. That is exactly what I expected, by setting the driver to 1.2A and using the 3-element glass lens. So the lpm works correctly! I shall recheck the output again when my G-2 lens arrives.

Thank you for the solution described, you saved me a lot of money :thanks:

icahone said:

The reading is slow, around half-one minute and the beam is defocused so it covers the whole area of the TEC.
I guess it is better to wait longer for the reading with defocused beam than to use a very small TEC and burn it with a focused beam of 1-2W :thinking:

Click to expand...

I would surmise that with a 40mm X 40mm sensor your 100%
response time will be closer to 90-120 seconds than 30 seconds.
We have done the tests...

Using a smaller precision sensor with our broadband coating
allows us to test Lasers to 3.2 Watts with a 100% response time
of 10-15 seconds..


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Hi Jerry,

understood.
I just do not want to throw out money for getting higher precision. (30+$ for a good tec) I am not a laser builder just a hobbyist so it is fine how it works now. When I tested after 1min. the reading did not raise anymore so I assumed it was the max. The difference in reading times may be either in the coating or the heatsink mass.
Anyhow, I am satisfied, so thanks again and HNY!

icahone said:

Hi Jerry,

understood.
I just do not want to throw out money for getting higher precision. (30+$ for a good tec) I am not a laser builder just a hobbyist so it is fine how it works now. When I tested after 1min. the reading did not raise anymore so I assumed it was the max. The difference in reading times may be either in the coating or the heatsink mass.
Anyhow, I am satisfied, so thanks again and HNY!

Click to expand...

As long as you are happy with your results... that's all that
counts for you.

BTW... Once the readings stabilize you have hit the 100%
reading time. The accuracy also depends on the linearity
of your coating over its range and the accuracy of your
calibration source..

Likewise HNY....:beer:


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Hi Jerry,

my G2 lens arrived today so I did new tests, using a reference laser, my red dilda V1. Assuming it is 200mW, I got the readings below.

Used diy laser with M140 driven by diy LM317 linear driver@1.25A, with double RCR123A nominal 1000mAh/3.7V batteries (4.04V by test) used:
- 3 element glass lens: 1170mW
- G2: 1502mW

Just to mention, the full cycle of measure start, stabilizing, getting back the TEC to initial values last ~2.3min (dilda) - 3min (diy), so the stabilization phase last only those 1-1.5min. as I assumed earlier.

Even if my dilda is putting out around 180mW (I doubt, with 3.7V nominal batteries), I am around 1350mW with the G2 lens. That is fine, I do not want to push my device further. It is getting warm after ~1min. of usage only, that is fine for me. My next project with the 9mm diode may reach the 2.5W, but the duty cycle will be really short.

icahone said:

Hi Jerry,

my G2 lens arrived today so I did new tests, using a reference laser, my red dilda V1. Assuming it is 200mW, I got the readings below.

Used diy laser with M140 driven by diy LM317 linear driver@1.25A, with double RCR123A nominal 1000mAh/3.7V batteries (4.04V by test) used:
- 3 element glass lens: 1170mW
- G2: 1502mW

Just to mention, the full cycle of measure start, stabilizing, getting back the TEC to initial values last ~2.3min (dilda) - 3min (diy), so the stabilization phase last only those 1-1.5min. as I assumed earlier.

Even if my dilda is putting out around 180mW (I doubt, with 3.7V nominal batteries), I am around 1350mW with the G2 lens. That is fine, I do not want to push my device further. It is getting warm after ~1min. of usage only, that is fine for me. My next project with the 9mm diode may reach the 2.5W, but the duty cycle will be really short.

Click to expand...

Post about it Might want to move this message to him, to the correct place.

-Shane

Ahh, okay.
One can either move or delete my post surely if needed.
It was not really addressed to Jerry but anyone who is reading this thread.

icahone said:

Hi Jerry,

my G2 lens arrived today so I did new tests, using a reference laser, my red dilda V1. Assuming it is 200mW, I got the readings below.

Used diy laser with M140 driven by diy LM317 linear driver@1.25A, with double RCR123A nominal 1000mAh/3.7V batteries (4.04V by test) used:
- 3 element glass lens: 1170mW
- G2: 1502mW

Just to mention, the full cycle of measure start, stabilizing, getting back the TEC to initial values last ~2.3min (dilda) - 3min (diy), so the stabilization phase last only those 1-1.5min. as I assumed earlier.

Even if my dilda is putting out around 180mW (I doubt, with 3.7V nominal batteries), I am around 1350mW with the G2 lens. That is fine, I do not want to push my device further. It is getting warm after ~1min. of usage only, that is fine for me. My next project with the 9mm diode may reach the 2.5W, but the duty cycle will be really short.

Click to expand...

Which is what I stated in Post #423...

Any accuracy in your readings will depend on your
assumptions of the output of you "200mW" Laser.

Your measurements will allow you to getrelative
measurements. (One is more powerful than the other)


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Does anyone have a good tutorial for a beginner on building a LPM for under $50?

laserlight84 said:

Does anyone have a good tutorial for a beginner on building a LPM for under $50?

Click to expand...

Will this module be okay to use?
Module Thermoelectric Tecnologic Power Generator Tec 6 6mm x 8 3mm Laird Compay | eBay

I can't find the spec sheet for this particular tec module. I found on the manufacturer's website similar sized modules and this should have a Qmax of around 3W.