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Oh hey look what I found
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DIY Thermal LPM for under $50
- Thread starter 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?
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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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icah93
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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?
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?
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.
I just found your post. Nice design. The board layout seems to be missing (or I don't know where this forum hides attachments).
loreadarkshade
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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?
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?