sketch only works with when reading one analog pin.

Projects Programming
1

I was hoping that someone could help me out. I'm very much a novice when it comes to arduino.
I have posted the code for my project on bitbucket for you to take a look at.

The projects purpose is to read the analog pins, which I have temperature sensors hooked up to.
I have an android app that connect to the server and gets the temperatures for each probe.
As an example of my problem, I have probes connected to analog port 0,1,2.
0 = 118F water
1 = 37F water
2 = 87F room temp.
If I only have probe 0 hooked up, i get a reading of 118 for that probe. When I leave probe 1, both, the readings of probe 0 and 1 will become the same reading (85,85)

I tested it the other day, all seemed find at the beginning, probe 0 had an accurate temp of 250, and probe 1 was 45, and probe 2 was 47. Later on in the day I noticed that probe 1 and probe 2 temps were inaccurate, they were always within a few degrees of each other. Later on, I had to disconnect all three, and when I plugged them back in they all read the same temperature.
It seems that if I have only one probe connected, it doesn't matter if its connected to pin 0,1 or 2, the temp is accurate.
but if multiple probes were connected that's when I was having issues.
Does anyone have any idea what may be going on, or what I can do to troubleshoot the cause of this issue?
let me know if my description is confusing.

2

You read the channels very short after each other and as the Arduino has only one ADC (multiplexed) they influence each other.

One error

double readValue;

should be

double readValue = 0;

What you should try is to read the temp sensors in the background with some delay between them (or throw away the first read after switching pins. Then when a web request comes in than you give the "cached "values in return.

3

Thank you.
I did fix the readValue to readValue = 0; while I was troubleshooting.

I was also thinking of "Caching" the values, but haven't gotten to do that yet.

I've read a lot about having to add the delay. Do you think a day of 200 milliseconds is enough? or should just doing a read, then recording a read, then doing another read, and throwing away the first and last work just as well?
Once again, thank you for your help.

Joe