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# "Ratiometric Analog Output" and Arduino Uno interface

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#### SolarPlexus

##### Newbie level 3
Hello all,

I'm trying to interface a pressure sensor (specifically, a Honeywell NSCSANN015PAUNV piezoresistive pressure sensor) with an Arduino Uno analog input, but I'm not having much luck. The output from the pressure sensor is a "ratiometric analog output" with a pin corresponding to V+out and a pin for V-out. My problem is that I haven't found an effective way of rectifying the output signal for interfacing with an Arduino input pin.

I have created a standard curve for the pressures of this sensor and have found that the voltage across the pins at atmospheric pressure and 5V input is approximately 75mV. This makes sense, as according to the datasheet (https://sensing.honeywell.com/index.php?ci_id=142173) the nominal mV/V/Full Scale Span = 15 for a supply voltage of 5V (maybe I'm completely misunderstanding what this spec means?). Anyways, this standard curve is approximately linear, with 15mV intervals (yintercept ~ 0).

In order to integrate the sensor with the Arduino, my first thought was that I could use a simple, zero-gain differential amplifier circuit (with an LM741 Op Amp and 10kOhm resistors). Unfortunately, the output from this circuit is only 65mV at 5V, which contradicts what I found when testing the pressure sensor on its own. Other voltage readings were similarly incongruent. I don't know how to get an accurate reading of the output from this sensor with my Arduino, and I've tried several LM741 arrangements to no avail. I would appreciate any advice on this matter, and whether or not I'm going about this measurement all wrong. I'm still a bit fuzzy about what "ratiometric analog output" means in this context.

Hi,

The output of this pressure sensor is differential and has very small amplitude <65mV. In your scheme you are handling the output of the sensor as single ended signal. Single ended signals perform very poorly in noisy environments. In your case your signal of interest is very small that it is even comparable to power supply noise of your system. I would sugegst you to use Instrumentation amplifier [1] to amplify the differential signal output of your sensor, and connect Single ended output of differential instrumentation amplifier with Arduino Uno Analog input. You will need to give about gain of 80 to 100 to the signal. And I would suggest you to use single supply instrument amplifier such as INA126[2], isntead of 741 which requires dual supply.

[1]. https://en.wikipedia.org/wiki/Instrumentation_amplifier
[2]. https://www.digikey.com/product-detail/en/INA126P/INA126P-ND/254672

Regards

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