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DIY Thermal LPM for under $50

MarioMaster

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Oh hey look what I found

o7amOtW.jpg
 



Cyparagon

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Does the zero adjust really need that much range though? Or is it more a low BOM count you're going for here?
 

MarioMaster

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Does the zero adjust really need that much range though? Or is it more a low BOM count you're going for here?

I was going for low BOM count but I am currently doing some testing and plan on updating some component values to make some adjustments less fiddly
 

icah93

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Feb 5, 2009
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Today I decided to build the circuit (V2).

While powering it from 2 different batteries, it does not work at all, there is no voltage change when heating the TEC at all.

When powering only the V1 side (and jumpered), it works but it is impossible to zero the initial voltage,
it always remains in the negative range (best -600-700mV).
When radiating the TEC with a 200mW laser the voltage moves
around 20mV total, getting 10mV sensitivity, that is not good enough.

I have rechecked the circuit and the components many times and found everything okay.
The only reason for not being it sensitive enough can be the TEC I guess.
Now I am using a 60W 15V TEC that I used previously with another opamp circuit which worked fine (LM328). The TEC has 127 junctions.

Can it be that it is not sensitive enough in the 100mW-2000mW range with this opamp and that is why it does not amplify the voltage to a reasonable level?
 

sk8nfool

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Jan 14, 2019
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Yup, a very simple circuit that is also very effective.

As per request here's a circuit board layout
Red is the top layer, blue is the bottom. The circuit board has a large ground plane to eliminate noise.
lpmtop.PNG

lpmbottom.PNG

I just found your post. Nice design. The board layout seems to be missing (or I don't know where this forum hides attachments).
 
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Dec 14, 2020
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My DMM oscillates when i connect the virtual ground for zeroing :(
I am in dual rail mode, the 2nd op amp of lm358 is properly terminated as per the datasheet.

It zeroes just fine, but oscillates 100mV at 2Hz

the oscillations stop when I connect DMM- to GND directly and skip the zeroing

What is going on?
 




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