I am using a load cell to measure a certain force on the load cell. I found a tutorial on instructables and followed it and the load cell works (more or less). The load cell only goes to 1kg, but the problem I have is flucations in the readings. For example:
0,32348
0,38668
Are taken with the same force on it (this is in N). Is there a way to make the load cell more stable (add some electronic component in between to stabalize the readings?)
I also use the INA125 amplifier. What I would like is to get as stable readings as possible (I know it depends on the INA125 too).
Any input from people who know more from electronics than me?
This is the tutorial I followed: http://www.instructables.com/id/Arduino-Load-Cell-Scale/ I didn't use the LCD display though.
Thanks in advance!
That circuit is fairly simplistic.
A good load cell anplifier shouls give 1 part in 10000 repeatability.
The amplifier is the important bit.
Iv only ever bought them off shelf and they are expensive.
That ic should give better results than that though, depends on the components around it.
Could it be the resistor i use as gain? I know resistors are made in different accuracy. I use a 68 ohm one, but if it differs 5% or 10% (depends on the manufacterer) it could explain a part of the flucations.
If you search the forum you will find this chip has been discussed before.
Can you post a picture.
Your results indicate it to be working but with some variability.
The link you posted has a picture showing breadboard being used.
This is a bad idea for this type if circuit, solder it with pad board.
The resistor's accuracy refers to how close it is to its rated resistance. That doesn't mean that the resistance fluctuates when it's in use.
It's not likely that the InAmp is outputting fluctuating voltages but more likely that the Arduino is doing a poor job reading the InAmp's output. What else does your circuit include? If you have blinky LEDs somewhere or anything else using the analog ports that will affect the accuracy of the Arduino's read of the InAmp.
I have a hall sensor connected to the arduino too to read the rpm of my motor. Could the problem be because of the wires i use? Those are on average 20-30cm long (from load cell to arduino board) and from hall sensor to arduino board.
For the rest i have nothing but the INA 125 on the board. All connected with wires though. No soldering.
Any noise on the lines between the InAmp and the load cell is going to be amplified greatly and the motor would be a good source of that. Maybe you can try wrapping the wires in foil and connecting the foil to GND.
I never saw any problems with using a breadboard with an InAmp. Also, the InAmp is designed to eliminate noise in the power lines so that's not a likely source either. Sure would be nice if you had an oscilloscope to check things out.
I will check on monday. The flucations also appear without a load yes. To be honest (I will check tonight to be sure), the load is good untill 1 gram. But if I want to set the motor thrust to 2N it is difficult to set it as a constant 2N (even with constant rpm) it flucates a lot.
Chagrin:
Any noise on the lines between the InAmp and the load cell
I never saw any problems with using a breadboard with an InAmp. Also, the InAmp is designed to eliminate noise in the power lines so that's not a likely source either. Sure would be nice if you had an oscilloscope to check things out.
Iv not used one of thos but have definatley had problems with op amps.
Poor contact being the most common problem.
Wires are most likely scource of pickup though, twisting them and keeping the same length can help.
Hi, are you using the circuit as in the instructible's item, if so it is missing bypass capacitors at the supply pins of the INA125.
Please read the spec sheet for the INA125 and not instructible's.
In fact the instructible's circuit uses the arduino 5V as the load cell reference/excitation.
The spec sheet uses the specifically designed selectable reference pin to do this job.
In fact the instructible's sets up a 5V reference, then doesn't use it...
[soapbox] instructible's..... ahh whats the use.. waste of good soapbox code tags..[/soapbox]
Hi, yes like that, pin4 should be connected to pin15, that will then make 5V at pin15 and 4.
The capacitor as you have drawn it, as close as possible to the two power pins.
