Analog read problem with T4.1

[Keith B]

Hello,

I appear to be having a problem with analogueRead using T4.1

I have a simple setup, a potentiometer wired to 3.3v and Gnd, with the sweeper pin connected to A14.
I am reading the analog value using analogRead(14) and simply displaying this on the serial port.

As I sweep the potentiometer, I get value printed out from 0 to 1023 as expected. However, around the centre point there is a gap between 490 and 590 ( when turning the pot CW) and a gap between 560 and 460 when rotating the pot CCW.

I get the same results when connected to A15 as well.

Any ideas when this could be?

Thanks in advance
Keith

 

[Keith B]

After further tests and searching on this forum, I believe I've got a fix in adding a pinMode(A14, INPUT) line in the setup code.

Not sure why this would fix the problem, but it appears to work.

 

[el_supremo]

Just an FYI: pin 14 and A14 are not the same thing. pin 14 is the analog pin referred to as A0. A14 is on pin 38.

Pete

 

[MarkT]

Any ideas when this could be?

I think this is the pin being in Schmitt-trigger mode, ie deliberate hysteresis circuit is active. I suspect this may
be the chip default at reset (to prevent power drain from floating inputs). I presume setting INPUT selects a
truely floating input mode - but this is only my guess.

 

[jonr]

Possibly different on the T4, but "INPUT" means "digital input". So either don't use pinMode() at all or use pinMode(n, INPUT_DISABLE).