What is the frequency of the signal you are measuring?
There is no gain on the differential amplifier.
Vout = (V2-V1)*(R3/R1)
Therefore:
Vout = (V2-V1)*(10k/10k)
Vout = (V2-V1)*1
Increase the 10k resistor going across the inverting input and the output of the differential amplifier to 3M resistor.
That would be a gain of 300 which should be suffice for the arduino adc.
There is no gain on the differential amplifier.
Vout = (V2-V1)*(R3/R1)
Therefore:
Vout = (V2-V1)*(10k/10k)
Vout = (V2-V1)*1
Increase the 10k resistor going across the inverting input and the output of the differential amplifier to 3M resistor.
That would be a gain of 300 which should be suffice for the arduino adc.Will do first thing tomorrow. Thanks!
But what is the use of the central trimmer? Sensitivity?
Is worth trying to get rid of the 10mV of common mode voltage left over after the first stage?
Another possibility is getting an instrumentation amplifier IC. All you need is a gain resistor.
http://www.farnell.com/datasheets/1837576.pdf
LM741's will be replaced by 14pin 4ex RC4136 or TL084 in definitive version.
It does not amplify anything, but manages to reference the signal to ground effectively:
I am just wondering that the trimmer (Cermet 100kOhms) is affecting the sensitivity but not amplifying?
Thusly should the 10k resistor with the question marks be replaced by a 100k or 1M Resistor?
Before this I did 3 test boards, I tried solving it on my own but I have only solder burn marks to show for it...
Edi: Added extra view with a previous 4 ex TL084 - that did not work - doing the LM741 version to be able to trouble shoot it.
Now the output must be converted from it's 0.01mv/0.30mV range to the Arduino ADC 3.2mV/3.3V range.
That means that each 0.01mV must become about 3.2mV, or amplified 320 times.
No worries for an Op Amp, 10kOhm on the positive and 3MkOhms between the negative and the output! No?
He says its going to a micro so can't he just calibrate it in software? Then he could use general purpose op amps.
He says its going to a micro so can't he just calibrate it in software? Then he could use general purpose op amps.
He says its going to a micro so can't he just calibrate it in software? Then he could use general purpose op amps.
A couple degrees change in temperature will destroy the calibration.
With analog switches there are various ways he could make his own auto-zero mechanism of course.
I am not surprised that the trimmer isn't actually altering the gain of your circuit. Nodes C and D from your original schematic are merely buffered versions of A and B.
The way you have your circuit wired, you have a gain of exactly 1.
You need to connect the inputs of the differential amplifier to the outputs of the first two opamps, not the feedback nodes. See attached image.
Thanks to forum suggestions, I was able to set up basic three wire load cells to have insignificant drift (less than 0.01mV per day).
I've tweaked that circuit during the last 2 weeks (long test times) and it's better than what I can measure
Now the output must be converted from it's 0.01mv/0.30mV range to the Arduino ADC 3.2mV/3.3V range.
That means that each 0.01mV must become about 3.2mV, or amplified 320 times.
No worries for an Op Amp, 10kOhm on the positive and 3MkOhms between the negative and the output! No?
Not really, I have about 1.645 V of common mode voltage to remove and the noise on the ground is higher than my signal (must use 6V Samsung phone chargers).
Thanks to forum suggestions, I was able to set up basic three wire load cells to have insignificant drift (less than 0.01mV per day).
I've tweaked that circuit during the last 2 weeks (long test times) and it's better than what I can measure
Now the output must be converted from it's 0.01mv/0.30mV range to the Arduino ADC 3.2mV/3.3V range.
That means that each 0.01mV must become about 3.2mV, or amplified 320 times.
No worries for an Op Amp, 10kOhm on the positive and 3MkOhms between the negative and the output! No?
Not really, I have about 1.645 V of common mode voltage to remove and the noise on the ground is higher than my signal (must use 6V Samsung phone chargers).Even if you are learning a lot doing it this way - take a look at the AD8237. This tiny (and cheap) Diff-Amp will -with some low tempco-Resistors - do it much better then you can do it....
BTDT.
Good luck
I'm going to do a final test board with a RC4136N.
I'm going to do a final test board with a RC4136N.Why? Do you not have access to decent precision op-amps?