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Topic: Amplifying sensor output (Read 2081 times) previous topic - next topic


I am currently trying to interface a MR rotation sensor to my arduino.

The sensor has 2 analog outputs of 2.5V+/- 0.1V. That is to say; if one output is 2.6V, the other is 2.4V.

I would like to take this output and manipulate it using an omp amp so that it is roughly in the range of 0-5V for use in the arduino's ADC.

I have been experimenting with a range of set ups and checking the results with a multimeter. Without the op amp plugged in, I have verified the sensor behaves as expected.

If I set up the opamp to provide an expected amplification of 10X, and plug in the sensor, the sensor output drops to 0.7V and the opamp output is 4.0V. However, at the point, the sensor does not seem to operate, as the output does not change in the presence of a magnetic field.

I believe my problem might be the Vcc and grounding I have used. Currently I have linked the 5V output and GND of the arduino to a breadboard, and linked all the required voltage inputs (from sensor and opamp) to this. Can anyone else suggest the problem and how to solve it?

Many thanks


Drawings necessary, that you try to implement.
and model/type of sensor as well, or data sheet specification



It appears you selection of the OPA was not the best.
No wonder, that voltage drops to 0.7V, as you apply signal from the sensor
directly to the input without matching network.
I'd not use this OPA.
Try to find something better, IC able to operate from single power line +5V
For start, check on LMP2021/22


Thank you for the advice. Could you please clarify what 'network' you are referring to when you suggest I need to match them? What about the LMP2021 makes it suitable to my application?


Feb 23, 2011, 02:28 am Last Edit: Feb 23, 2011, 02:31 am by Magician Reason: 1
O'K let me explain process, so next time you will be able teach others -):
Don't know why you stop your choice on LM3900, but first things to do it to
find data sheet on chip.  
I like:   http://www.alldatasheet.com
There is a big chance it will include application drawing, formula for calculation gain
parameters, power supply min and max, noise etc, etc.
(I've attached a pics and docs).
You will save a lot of time, because all this application details from manufacturer
engineer, who design a chip itself, anyone else knows better than they are?
Regarding LMP2021, I just came across it looking throw National Semiconductor
"Industrial Sensor Interface  Solutions Guide  national.com/industrial" document.
Doc size 1.4Mb, can't post here. Google pops up it for me on
"industrial differential amplifier" search pattern.
If for some reason IC difficult to find on a market, look on others "big monsters" sites,
TI - Texas Instruments, Linear Technology and so on.
Name of the guide and section ask on google, bastard knows everything -):



As I understand you need non-inverting amplifier with 2:1 amplification. I think this tutorial can help you:

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