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Author Topic: Load sensor amplifier  (Read 3202 times)
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I would buy this IC http://www.ebay.com/itm/INA125-Instrumentation-Amplifier-w-precision-voltage-reference-INA125PA-OpAmp-/181049159026?pt=LH_DefaultDomain_0&hash=item2a275eed72
I have used INA125's for load cell amps in the past and this has the benefit of a precision voltage that you can excite the load cell with.

For schematics get the datasheet for the IC and read it.
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I'd'a thunk that the vendor of the loadcell hardware would have sold a compatible, tried-and-tested, electronics package with it?

They often do, but marketing to the industrial base they tend to be pretty expensive. Omega Engineering company sells lots of load cells and accessories for them.

Lefty
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$0.99 50 x Resistors 250 Ohms OHM 1/4W 5% Carbon Film
$0.99 50 x Resistor 10K Ohm 1/4W 0.25W 5% Carbon Film
$0.99 3 x 0.1uF 50V Radial Capacitor Tantalum
$14.28 2 x INA122 Precision Instrumentation Amp, 2-36Vsup R-RO

Total: $17.25

worth it?
« Last Edit: March 05, 2013, 01:19:51 pm by TrailerTrash » Logged

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$0.99 50 x Resistors 200 Ohms OHM 1/4W 5% Carbon Film
$0.99 50 x Resistor 10K Ohm 1/4W 0.25W 5% Carbon Film
$0.99 3 x 0.1uF 50V Radial Capacitor Tantalum
$14.28 2 x INA122 Precision Instrumentation Amp, 2-36Vsup R-RO

Total: $17.25

worth it?


Priceless!  smiley-wink
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What you'll find is that when the cell is at rest it will report some non-zero voltage (load cells are never perfectly balanced), and then you'll want to get the largest voltage swing possible from that point when load is applied. You'll be doing a lot of fiddling with the gain resistor when you're setting this up and will want to have 500R or 100R or maybe even 10R trimmers on hand to do that.
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$0.99 50 x Resistors 250 Ohms OHM 1/4W 5% Carbon Film
$0.99 50 x Resistor 10K Ohm 1/4W 0.25W 5% Carbon Film
$0.99 3 x 0.1uF 50V Radial Capacitor Tantalum
$14.28 2 x INA122 Precision Instrumentation Amp, 2-36Vsup R-RO

Total: $17.25

worth it?

As Lefty say's, 'priceless', though one has to wonder why on Earth, or in your case 'a rogue planet called Nibiru' would you design a circuit with a precision op-amp costing $14 and buy for less than one dollar, 50 resistors that are a inferior 5% carbon film?
I can see that the two 10kΩ resistors probably do not need to be exactly 10kΩ, but for me, it's about good design practice.
Out of the 48 resistors left over, a time will come where you wished you had 1% metal.
_____
Paul
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What you'll find is that when the cell is at rest it will report some non-zero voltage (load cells are never perfectly balanced), and then you'll want to get the largest voltage swing possible from that point when load is applied. You'll be doing a lot of fiddling with the gain resistor when you're setting this up and will want to have 500R or 100R or maybe even 10R trimmers on hand to do that.
too late, i bought all the stuff already
you think i should replace the 250ohm resistor with a 250k ohm Trimmer Potentiometer? but they have 3 pins. draw it.

http://www.ebay.com/itm/10pcs-3296W-101-100R-ohm-3296W-Trim-Pot-Trimmer-Potentiometer-new-/330810783476
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« Last Edit: March 05, 2013, 07:40:41 pm by TrailerTrash » Logged

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What you'll find is that when the cell is at rest it will report some non-zero voltage (load cells are never perfectly balanced), and then you'll want to get the largest voltage swing possible from that point when load is applied. You'll be doing a lot of fiddling with the gain resistor when you're setting this up and will want to have 500R or 100R or maybe even 10R trimmers on hand to do that.
too late, i bought all the stuff already
you think i should replace the 250ohm resistor with a 250k ohm Trimmer Potentiometer? but they have 3 pins. draw it.

http://www.ebay.com/itm/10pcs-3296W-101-100R-ohm-3296W-Trim-Pot-Trimmer-Potentiometer-new-/330810783476


To use a pot as a variable resistor you just wire to the wiper terminal and to only one of the fixed terminals. Presto variable resistor.
Lefty

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http://www.ebay.nl/itm/121022291106?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
24 bit ADC with I2C com for load cell amplification at a low cost ready to use.

Paco
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Never to old to learn and I learn every day

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http://www.ebay.nl/itm/121022291106?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
24 bit ADC with I2C com for load cell amplification at a low cost ready to use.

Paco

Very impressive find. I looked for it on the US ebay site and found it here:

http://www.ebay.com/itm/121022291106?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

And ordered one. With that kind of resolution one can directly read low level wheatstone bridge devices without requiring amplification at all. Lets see how good it's low noise performance is when it arrives.

Lefty
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I'd be interested in your results, Lefty. Seems too good to be true.
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Hey! As fate would have it; I am currently a scale technician--previously worked on helicopter's that towed stuff (they're pretty cool) technician--and I found Arduino, explicitly from my interest doing this same project. How has it turned out? & "what-all" have you pieced together to get it done?

I have lots of experience on the hardware and end-market commercial software for scales;

REALLY look forward to hearing about this

Thanks!
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