Minimum ADC input value ????

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi all,

Has any of you, during experiments with ADC, been able to get the lowest input possible ?

I have a small voltage and want to read it with the Arduino but I'm trying to avaoid uadding external circuitry like an OPamp for boosting the signal so I need to know the minimum voltage I'll be able to read

Tnx

2

Let's do the math.

Using the standard hardware (i.e. using the internal Vref) it measures 0 to 5V. It's a 10 bit ADC, which means 1024 steps.

5V/1024 steps = 4.88mV/step

So, 4.88mV is the smallest measurable input.

A different reference voltage (via an external reference) will reduce the range measured with a corresponding reduction in V per step (e.g. a 3.3V Vref would result in 3.22mV/step).

-j

3

OK for that :slight_smile:

But I f I use an external Vref, like 1.5V, I can increase the resolution in the area of 0-1.5V and it gives me a 1.3mV.

Is the Atmel chip able to read it ?

My sensor (MPX5500) has an output of 9mV/ KPa and I am only interested by the 0-150 KPA area.

Tnx

4

Have a look at this page : analogReference() - Arduino Reference

5

I've read that already but good as a reminder.
So I'll give a try with the internal 1.1V and how it goes.

Tnx for all :wink: