Go Down

Topic: Arduino Due Analog Pin Impedance (Read 516 times) previous topic - next topic

Does anyone know what the impedance is on the analog pins on the Arduino Due?

I've got a sensor that's resistance ranges from 25 to 375kohms and need to know this to see if its going to work or not.

Thanks.

Graynomad

AFAIK it varies with the speed you run the ADC, table 46-35 shows the "Source impedance values" and they range from

10k with ADC clock of 20MHz
to
274k with ADC clock of 1MHz

It takes 20 clock cycles to take a reading so you can do the maths as to the sample rate. As for what rate is set by the Arduino init code I have no idea but I would assume they went for the fastest.

In other words the faster you want to sample the lower the source Z has to be.

This is for 12 bits, for 10 bits the Z can be slightly higher, ie 14k and 353k for the above speeds.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

Got it.  I understand.

I read the table you are speaking of a wasn't sure if that was what I was looking for or not before posting.

Go Up