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 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.
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.
why doesnt an amplifier help the arduino?
it would be 2 times cheaper...
the ISL28130CEZ can do G=10000 with 100nV sensitivity... according to the datasheet...
Chagrin:
The load cell is a wheatstone bridge. Not sure why you'd be adding resistors?
I need to add resistors as a "dummy" load cell since the ones I have aren't "full-bridge" I could also combine 2 or more cells into a bridge but that seems like a waste of expensive parts to me.
Chagrin:
you might not be able to do this without some kind of amp.
That's why I started this topic, it's less about the cells and more about the OPamp
I'm really starting to get that drowning sensation, you know water over your head
The ISL28130CEZ isn't "available" where I'm at, I can of course get a hold of it but I'd like to get things moving.
The LM358AN has been suggested by some, It's seems to do the things I need, Sadly I have little experience with OPamps beyond the Cmoy, so I'm not really sure.
The video uses a full bridge sensor but you just need two resistors and/or a pot to complete the bridge. The video uses a true instrumentation amplifier, an AD620, which is expensive but easy to use.
18 - 24 bit delta-sigma ADCs are a better fit for this type application. A delta-sigma ADC requires less signal conditioning circuitry, less amplification, and has greater resolution than the Arduino SAR ADC.
I don't really need any higher resolution than 1 bit, I intend to use the load cell for weight increase detection not measuring, I'd like for my Arduino to detect if the base value of the load cell increases by say 10Kg not 5Kg not 1Kg, In fact I'd be very happy if it didn't even notice a 5Kg increase.
So a high resolution or great accuracy is not something I'm in need of (Low noise is though).
The less expensive the better (not that I'm cheap I'm just thinking large scale).
I bet the ADC you talk about fat16lib, is great it might even make my life easier, And if you feel that It's what's best suited for my application than I'll try it.
If you have three wires coming out, I think you have two resistor elements in the strain gage, one is on the piece of steel that strains, and the other is in another place where it is an offset for temperature correction.
growerdick:
If you have three wires coming out, I think you have two resistor elements in the strain gage, one is on the piece of steel that strains, and the other is in another place where it is an offset for temperature correction.
They make up half of a wheatstone bridge.
You think?
Your assumption is sadly not correct.
The strain gauge is a voltage divider. It works alot like a potentiometer only the strain gauge only changes it's resistance value by a couple of ohms at full load. There is no resistor in there for temperature correction. However by using two Half-bridge gauges, one as a pressure sensor and the other as a reference for the amplifier you'd get your temperature correction.