Analog pins questions

I assume these work as arduino pins do apply a voltage and get a number in return 0 - 1023?

questions,

can the range be changed to 1v to 3v thus improving the resolution?

The Due is a 10 bit pin giving 0 - 3.3v 4000 points. can this be done?

I am trying to construct a specific gravity sensor using differential pressure specifically measuring between 1.0 to 1.1 . the sensors are sensitive enough.

any help would be appreciated.

thank yoiu
steve

Hi @murmsk

Hereâ€™s the doc:

Analog inputs are similar to the ones in the Arduino world but differ in some respects, like, 0-3.3V input and 0-4095 range. The input impedance of the analog inputs is lower on the ST Micro processors so depending on what you are measuring, you might need a small amount of external circuitry.

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@murmsk, as (the amazing) @bko pointed out, the Photon ADC provides 12-bits of accuracy over a range of 3.3v, give a rough bit resolution of 806uV/bit. For a 1.0-1.1v range, that represents a range of 124 bit-count. You need to take into consideration the fact that the ADC reference voltage comes from the 3.3v supply, and any noise on the sensor input. Both will â€średuceâ€ť that effective 124 bit-count range.

You may be better served by expanding the input voltage using an op-amp input, with gain, in a differential or AC coupled mode depending on your signal. In differential mode, you would set one input of the op-amp at 1.0v (using a voltage divider for example) so that only the â€śdifference valueâ€ť of the input is amplified. With the right gain, the â€śdifferenceâ€ť of 0.1v could be expanded to the full 0-3.3v ADC range.

Using a AC-coupled input would amplify (as above) only the non-DC component of the gravity sensor but if the signal is low frequency, you may be better served with a differential configuration.

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You can also look at 16bit dedicated ADC boards with differential inputsâ€¦ makes for much less noisy sensor inputs and also have better resolution.

The ADS-1115 is an I2C bus based ADC with 4 x16bit channels and including a up to x16 gain amplifier built inâ€¦

I have a Oxygen sensor that produces a signal from of 0.55 mV to 55mV and with this chip in differential mode and x16 gain, I get super accurate and low noise signal without any op-amp circuitsâ€¦

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