I need your help. I would like to connect external analog signal to the Arduino nano analog input. But, I must get high resolution sensing, so I thought maybe there is a way to divide the income analog signal between 2 analog inputs. This way I will get low resolution changes via the first analog input and the high resolution changes in the second analog input and I will calculate it the result will be much wider than 0-1024 values.
But I don't know electronics, anyone here can advice me how to do that ?
There are some tricks using oversampling to get greater resolution, but the Arduino board is handicapped by not being designed with analog capture in mind, and the Atmel chip isn't completely separated internally between the analog and digital sections.
I concur with PaulS, use an external ADC. It is even more important with greater bit depth to pay attention to layout, power supply decoupling, noise, distortion, etc. There is something called ENOB, Effective Number Of Bits. Basically, the lowest bit or two is garbage because of the problems of noise, quantization error, distortion, etc.
What kind of resolution do you need? I mean really need. 24 bits is unrealistic without a -lot- of work. And at what speed?
The 32 bit ARM based Teensy 3 ($20) has a 16 bit ADC. The Teensy 3.1, current version, has lots of improvements over the 3.0 and the Due, including two ADC converters and 5V tolerant inputs (the Due and Teensy 3/3.1 are 3.3V chips).
Theoreticaly, with diferential amp (using op amps) you could, for instance, take 0-10V signal, then split it to upper and lover 5V and measure each individualy, but that doesn't really give you much greater precision (if at all considering all the other components). Then again, you could split it to more parts but then you are just implementing an ADC so no point in that. If you need more precision get a better ADC chip.
polymorph:
xzarth: If you "split" 0-10V, when the signal is above 5V, the lower is always 1023. When the signal is below 5V, the upper is always 0.
All you've really done is add one more bit of information.
Oversampling, or a higher resolution ADC with a lot of care put into low noise, low distortion, etc. Look up ENOB.
Yes, i know, that's why i said you don't get much more, if anything. And you can use single pin, you don't need to use two (basically you do need another one to control input voltage, but you could do it in smaller steps. Like if you had 0-5V input you could split it in 1V chunks and then amplify those to 0-5V range and measure those gaining a few more bits with same two pins. And yes, i'm avare that it almost certainly wouldn't be any more precise, it would just add more bits.
I should not be so hard on xzarth, I just realized that that is essentially how flash A/D converters work. Though flash converters are not used for better resolution, but speed.