Analog Inputs not working correctly at all!

Forum 2005-2010 (read only) Hardware Interfacing
1

Hello everyone!

I am trying to read 3 thermistors and spit it out onto a webpage. I am having some problems so decided to check out whats really going on.

I plugged the USB cable into the Arduino+EtherShield and just did (all the way to 5). Output below is with nothing hooked up to the board.

client.print(analogRead(0));
client.print(" - 1
");
client.print(analogRead(1));
client.print(" - 2
");

And got this as an output on the webpage:

1023 - 1
1023 - 2
931 - 3
833 - 4
717 - 5
649 - 6

I then wanted to see what happened without anything hooked up to the arduino... just the board itself (no shield) and did this:

   Serial.println(analogRead(0));
   Serial.println(analogRead(1)); (all the way to 5)

And got this for the output with no wires connected (kept floating... ok....):

415
407
369
332
290
304

And this when I hooked up 3 aInputs with everything (http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1254096639/3) but the thermistors:

0
0
0
114
179
219

What is happening to the analog inputs with the Ethernet Shield? Is their something I am doing wrong? >:(

2

So why would the first two analog inputs state 1023 when nothing is connected to them? Does it have to do with the Ethershield?

I never said anything was wrong with the arduino. (Just said the analog inputs weren't working :wink: )

3

Jut to reiterate what you are seeing is the expected correct behavior from your analogue inputs. They all behave like this. Look up floating inputs.

4

^Where I purchased it from

Mike: I now know that the floating values are normal.

5

So why would the first two analog inputs state 1023 when nothing is connected to them? Does it have to do with the Ethershield?

Following the links on Adafruit's site, I found a link to the schematic. Look at J2 (Far Right Side): http://arduino.cc/en/uploads/Main/arduino-ethernet-shield-05-schematic.pdf

Pins 1 and 2 of J2 which are Analog input 0 and 1 have external Pull-Up resistors on them.