I need and request as much help as I can get. Please offer what you might or point me elsewhere.

As an 85 yo 9-year non-professional student of sleep breathing, my goal is to log chest-belt extension-excursion data from my second piezometric belt (of two) into a text or csv file. My first belt and logger, purchased new, whole and mated, is great but too high cost to repeat.

An amplified and filtered analog voltage is to come from my piezometric belt that goes around my chest and/or abdomen to help with other breathing sensors.

My understanding is that the signal from the belt I have is 1mV (or ranges up to that) and that filtering out of 0.1 Hz and 70 Hz noise is desired. I also have a LabJack U3-LV data logger. My understanding of the well documented Labjack is that it will log analog data into a text file. I bought the used items separately on ebay.

My inquiry to Labjack—to their credit—drew this response I appreciated and paraphrase: 1 mv needs amplification before the U3 can make much sense of it. Something like and inAmp would do the trick. Filtering will need to be done in analog or post processing. "The Analog option requires building a circuit with desired filtering characteristics."

Thank you for considering this.

*********************

Other more extraneous information:

In blissful ignorance I gambled that the necessary amplifier and filter could be put together at reasonable cost, but I learned late that finding local electronics supply and techs is difficult. Gone are Allied, Radio Shack, Heath, not to mention small local vendors like our "Sparky's"—all long gone. Looking at Adafruit for boards or chips was above my head for choosing. Too much trial and error awaits. There are cell phone repair shops and techs but . . . a visit to one today suggested only a hobby shop for model planes and and other remote controlled items was the only suggestion. Surprising for the main city of a half million in a California county with a population of a million.

My bits of electronics experience was Navy Class C Radar School in '58 (of the glass tube era) followed by lower division college physics for engineering students with one major subsection, "Electricity and Magnetism"

 

What I see as a possibility is an alternative approach. Start with your sensor signal and use an instrument amplifier IC , along with an inexpensive, low power bipolar power supply +12 and -12 volts, with linear regulators to avoid noise. Then add the instrument amplifier to the supply, and use that amplified signal to drive a voltage to frequency converter, and feed that frequency into a computer "sound card port. Now software can interrogate the sound card and know the frequency, which directly correlates to the voltage. So that frequency can can be interpreted as a voltage and logged into a CSV data table.

 

The labjack U6 would seem to more more suited for direct connection to the belt signal after a filter. Likely a lot more expensive, even used.

https://labjack.com/products/u6
14 Analog Inputs (16-18-bit) expandable up to 84 AINs using Mux80 Expansion board
±10V, ±1V, ±0.1V and ±0.01V Voltage ranges

As was said above, a good instrument amplifier for the needed ±0.01V Voltage range into your U3 will likely work too.

 

I would consider an alternative sensor altogether.

You could create a very inexpensive sensor belt around a capacitive sensor concept.
Sandwich some metal foil or fine mesh between some layers of compressible rubber or foam, creating a variable capacitor.
The whole sandwich can be enclosed by a grounded layer to remove influence from external capacitance.

This capacitor can be part of an oscillator that will change frequency as the sensor is compressed, it's much simpler to measure frequency than low level analog signals.
I would build a simple RC oscillator into the belt, with a 3 wire cable: Gnd, Power and signal, now the cable can even be unshielded.

 

Some additional advice to the TS is that the first requirement is a better understanding of basic instrumentation systems, so as to be able to ask the right questions. Being able to ask the more appropriate questions to the correct people will often provide much more useful answers.

 

Hello All,

Slow to get back here, I appreciate the several responses and ideas. MisterBill2's last put his finger on a key reason for my being slow.

I hoped to quickly get with a local Makers group that will meet soon. It has an electronics subgroup I was going to ask for help—helps with the helps in MisterBill's initial, emailed response. Obviously, I have hit the books hard before pestering you and ACA more.

Thank you,

Jon