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Topic: OPamp (Read 2 times) previous topic - next topic

Thestrongestduck

Hi.

I am in need of some assistants, and was hoping that you guys might be able to help. I'm trying to find a suitable OPamp for a 45KG load cell, I've spent the last couple of days surfing the web hoping to find an answer and I sort of did, many of you suggest using the INA125 instrumentation amplifier, but here's the thing, I don't really need an accurate readout.

I'm in more of a need of weight detection than weight measuring, with a resolution of say 25KG. So I was hoping that a more basic OPamp would do. Or perhaps another device altogether if there is such a thing?

I do have some requirements for the amp, I'd like for it to work of 5-9V and have a adjustable gain using a resistor, if the output was fairly noise free.

Thanks in advance. 

johnwasser

What is the output of your particular 45KG load cell?
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fat16lib

I assume the load cell has no amplifier.  If it has typical ratings, a MCP3422 or MCP3424 would work well.

The LSB (Least Significant Bit) at full gain corresponds to about 2 microvolts.

http://ww1.microchip.com/downloads/en/devicedoc/22088c.pdf

This is an 18-bit ?? ADC with Differential Inputs. It has these features:

On-Board Programmable Gain Amplifier (PGA) with gains of 1, 2, 4 or 8.

On-Board Voltage Reference (VREF) Accuracy: 2.048V ± 0.05%.

I2C interface.

Here is an old post with some test code http://forums.adafruit.com/viewtopic.php?f=31&t=12269

Thestrongestduck

#3
Sep 06, 2012, 04:12 pm Last Edit: Sep 06, 2012, 04:32 pm by Thestrongestduck Reason: 1
Thanks a lot for the tips, I'm in no real need of a ADC though, since I'll be hooking it up to the arduino.

EDIT:
Hmm, haven given it more than 5 seconds of thought, I kinda see how it would work, maybe I should mention that I plan on using it in a Wheatstone Bridge configuration, measuring the 2 voltage differences between the resistors and amplifying that,

The load cell or strain gauge "not entirely sure which is which" have been scavenged from a bathroom scale, and is very similar to the ones that Sparkfun sell.   

Chagrin

The load cell is a wheatstone bridge. Not sure why you'd be adding resistors?

If the cell has the typical four wire colors (red, black, green, white) then you would connect red and black to an appropriate voltage (typically 5V) and the remaining two into the Arduino analog pins. The difference between the analog readings varies with the weight applied. It's a very small difference; you might not be able to do this without some kind of amp.

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