HX710B pressure sensor module issues

I am using HX710B pressure sensor module for my sphygmomanometer project on Arduino. The problem is that while using the formula (((16hx711.read()(2.98023224/10000000))-40)*760)/101.325 to convert ADC to mmhg, one sensor is starting the reading in -14, and the other at -105. Why is that?

Whenever troubleshooting the first thing you should do is output the raw ADC values. You should verify the read function provides a 16 bit or 24 bit number. Arduinos being basically an 8 bit device will have to make three reads to get the complete number. Is this being accomplished in your library?

Low cost pressure sensor from China. I would imagine it could leak. Simple test bring it to a pressure and clamp the tube going to the sensor (really tight, like vice grips tight). Then see how fast the decay is.

Has the OP considered that to help us help you, we'd want to see things like schematics and project photos and code in code tags?

Using an Uno?

The maths is also an issue

(2.98023224/10000000))-40)

2.98023/100000000 is a tiny number , multiplied by the analog reading then subtracting 40.
You may well be suffering rounding errors or numbers getting out of range, or your maths might be wrong .You need to think about this and try some values with your calculator , round off any numbers with too many significant figures .
Re arranging the equation so you multiply by the 760 first might yield better results ?? Try it

As others have said always start printing out the raw numbers to see if it’s working ok
?

Lack of calibration?

What is the output, in mV, of each sensor, measured with a DMM, when they are at the same pressure?

There is an example in the library for the HX710B. You should use it to sort out the numbers you think you are receiving before you do any project calculations.

Thanks. Oops, I guess your device has an on-board HX710B, so the output of the Wheatstone bridge in the sensor is not easily measured. So, never mind.....

But I wouldn't be surprised if, as I implied in my first post, that the sensors need to be calibrated before they give reasonable results.

In fact, I just found the following website says: "One thing to note is that after testing several sensors - they do not all agree in sensitivity and offset. Therefore, the user must CALIBRATE EACH SENSOR in order to provide an accurate representations of pressure."

You are prototyping a medical device (sphygmomanometer ... blood pressure sensor) and intend to manufacture it for sale to health professionals?

An electronic sphygmomanometer will definitely require calibration both at the factory and periodically in use. However this is not the issue. The sensor used must be stable enough to make it from one calibration date to the next without drifting out of tolerance. Should we assume thie

Also note, with low pressure sensors like this the Zero reading is never stable. Most often the controller will "measure" the output with a known Zero pressure and use that measurement to remove the zero offset.

You mention you verified the calculation " (((16hx711.read() (2.98023224/10000000))-40)*760)/101.325" by hand. Have you looked at each operand result to see if it overflows/underflows your processor?

Also there is a air constant leakage in the system the source of which I am not able to identify

Can you tell us what the "system" consists of? And how you determined there is a leak?

In any case as I am prototyping with manufacturing in mind....

Is this an exercise or a real thought of manufacturing a product?

If a product, have you considered quality control, verification of stability of "EVERY" device you mfg? Is a hobby bridge IC really the best part for a commercial product?

Have you considered..

repeatability
repeatability
repeatability
repeatability
repeatability
repeatability
repeatability
repeatabelty
repeatability
repeatability
repeatability
repeatability

Yep, when ever I see maths like this , there is more than likely a problem . Do as much of the maths outside of the sketch and , as I said look carefully at the order of calculation and sensitivity to value errors

Why didn't you try Google?

Hi,
Welcome to the forum.

I Googled;

2SMPP-02 Omron arduino

It has library and example code.

Tom.... :smiley: :+1: :coffee: :australia:

The sensor will not connect directly to the Arduino. You will need an interface board like the HX-711.
This sensor has 4 resistors connected together in a bridge configuration. When you apply pressure the resistors change resistance (slightly). To measure these changes you need a high gain amplifier/converter.

I'm guessing @TomGeorge's link seems to be for a different Omron sensor.

@anon90086852 Beginners tutorials is a place for posting guess what, tutorials aimed at beginners. NOT for asking questions about some project of yours. It says so in the description of the section. Therefore I have moved your post here. Please be more careful where you post in future.

You may want to read this before you proceed:-
how to get the best out of this forum

@Grumpy_Mike sure, will take care in future. and thanks

@TomGeorge isn't that a different pressure sensor?

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Thanks to all those who helped and added to this list.

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