Hello,
I'm trying to read a very small voltage, mostly I'm interested in if there is a voltage, however small, at all. I've read that the 10-bit ADC on the UNO board won't give me enough precision. I was able to follow this:
Building an Arduino DC Voltmeter - Udemy Blog and connct it to an LCD display.

I do have this HX711 sensor with a 24-bit ADC. From what I've found on it, it's used for weight scales, but could I use it to read little, if any voltage?

Am I going about this the wrong way? I don't need to know the actual voltage, only if there is any very small voltage present at all. I've heard people mention amplification... would that be more useful? I'm quite new to Arduino and electronics, I'm sorry.

legoleg:
I'm trying to read a very small voltage, mostly I'm interested in if there is a voltage, however small, at all.

You must be specific. How small.
All measuring devices have a limited range. e.g. Arduino's 10-bit A/D is ~1:1000
The voltages of the "thing" you want to measure have to be within that range.
Arduino's A/D, without preamp, can measure in quite small ~1mV steps with the right code.

The HX711 has a 128x preamp and onboard A/D.
But the "thing" you want to measure has to be within the range of the HX711's supply, superimposed on 4.3volt/2 = 2.15volt

We can give better advise if you tell us WHAT you want to measure.
Leo..

Wawa:
You must be specific. How small.
....

We can give better advise if you tell us WHAT you want to measure.
Leo..

Thank you for the reply! It's probably even be less than a millivolt that I want to measure... I'm basically generating tiny currents in a coil and trying to see if I can notice them, they would be momentary.

Floating or ground referred.
What is the frequency (The HX711 is slow).
Post a circuit diagram.
Leo..

I had to go read, but it would be a floating ground.

I'm not sure of the frequency, I don't think it would be thousandths of a second, probably on the order of a few hundredths.

The best I found for a circuit diagram is a completely different adc...
http://henrysbench.capnfatz.com/henrys-bench/ltc2400-arduino-voltmeter-module-user-manual/

Are there analogous pins on the HX711 that I could use? I think I understood the instruction in the link, it's just that that chip @\$20 is a little too much right now, but I'd try it if it was the right adc for the job.

I have the red/brown board pictured here:
http://hivetool.org/w/index.php?title=Interface_the_HX711_to_Pi

legoleg:
but I'd try it if it was the right adc for the job.

Which you haven't told us.

The HX711 is an instrumentation amp, followed by a 24bit A/D
It has differential inputs that have to be about mid-voltage.

The other board is just the A/D. Single ended input (ground referred).
0-4.096volt input because of the same reference voltage.

Two different animals.
Leo..

I'm not sure what all that means...

I need to see if there is a very small, very short-lived voltage present... single millivolts, probably less, lasting for maybe a couple hundredths of a second. I'm just experimenting and I don't know the specifics yet.

I understand that the 10bit adc on the UNO doesn't give enough precision.... 1024 steps between 0 and 5 volts isn's small enough. I have an HX711 with a 24bit adc, but I don't know if I can access it as an adc... or is there another way to determine if a very small, very short voltage is present?

legoleg:
I understand that the 10bit adc on the UNO doesn't give enough precision.... 1024 steps between 0 and 5 volts isn's small enough.

Make that 1024 steps between 0 and ~1.1volt.
~1mV resolution with 1.1volt Aref enabled (post#1).

Tell us more about the short pulse.
There might be other solutions you haven't thought about.
Leo..

Hi,
How are you going to see your signal in noise, you will need a well grounded bench and use differential inputs to detect what you need.
Look up ECG, Electrocardiogram, and arduino.
They make shields for these measurements with arduino, sound like the input signal level you are looking for.

Tom.....
What is your electronics, programming, arduino, hardware experience?

Thanks for the idea about EEG, I'll look into it.

In an experiment I did with only a multimeter and my coil I was able to see a little voltage generated, I think it was about a millivolt. I'm just passing a small magnet through it to see what I can see.

Id like to replicate that with the Uno, but then also see if I can recognize that even smaller voltages are generated. Is there a way I could use the HX711 "badly" as an ADC to see how it works? Even if it's noisy and slow to see it's drawbacks?

Is there another way to recognize that a small voltage is present from when it's not? I don't need to know how big it actually is, just if it is there.

I'm an ok programmer, but don't really have any electronics or Arduino experience. I've soldered before and put together a couple of USB battery packs from old cell phone batteries and ebay parts, and they haven't blown up yet. I can follow a tutorial and I've been able to use a few sensors so far. I'm hoping to be able to make a 6 legged combat creature not walk into walls soon, i think i have a basic idea of how that would work.