# 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

Here’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 “reduce” 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 “difference value” of the input is amplified. With the right gain, the “difference” 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. 1 Like

You can also look at 16bit dedicated ADC boards with differential inputs… 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 in…

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 circuits…

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