My Arduino mega 2560 pins are inputing random numbers

[nonkapa]

Hi, I have an arduino mega 2560. When I trying to take an input from a sensor (for example a voltage sensor) the pins of the arduino are inputing random numbers instead of inputing the output of the sensor. Even when I completely remove the sensor for the arduino it is still inputing random numbers istead of inputing 0. Any ideas on what may cause this?

[Koepel]

Welcome to the forum.

When a pin is not connected, then it is "floating". It is picking noise and static electricity from the air. The impedance of a input pin is in the hundreds of GigaOhm.

[PerryBebbington]

@nonkapa

Even when I completely remove the sensor for the arduino it is still inputing random numbers istead of inputing 0.

What makes you think an unconnected input will read as 0?
Have a read of this for an explanation of the reason this is not the case: Buttons and other electro-mechanical inputs (introduction)

As for your sensors, without knowing what they are or how they are wired it's difficult to offer advice that isn't just guess work. Please post a schematic, details of what components you have and your code.

[nonkapa]

I forgot to mention that I had it working before a week or so... when I was disconnecting the sensor the input that I was reading in the Serial monitor was 0

[nonkapa]

Hi, I will read the post. Do you recommend some program or a site for me to make the schematic?

[nonkapa]

That is my code.

#define vpin A1

float vraw;
float vout;

void setup()
{
pinMode(vpin,INPUT);
Serial.begin(9600);
Serial.println("Voltage: ");
}
void loop()
{
vraw=analogRead(vpin);
vout=(vraw/1023)*25;
Serial.println(vout);
delay(1000);
}

[Grumpy_Mike]

@nonkapa

I forgot to mention that I had it working before a week or so.

That just means you were fortunate, a pin can read anything and a digital pin can only return zero or one ( high or low), so it matters little what it did a week ago. The thing is it is not stable and the input is floating.

If this is from a sensor it is often the case that the common ground connection is not made.

To learn about floating inputs and how to deal with them read this
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

And to learn why you need a common ground for both inputs and outputs read this
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

[PerryBebbington]

How to make a schematic you can post.

When you submit a question on the forum you will usually need to add a schematic (circuit diagram). The tutorial that follows will explain some ways to create a useful image; however lets start by explaining how to add the image to your post. Its easy. Having created the image all you need to do is : Save the image somewhere convenient - maybe your desktop Start your post, and place the cursor (insertion point) where you want the image to be shown; [upload image to forum] 3: click th…

[srnet]

@nonkapa

I forgot to mention that I had it working before a week or so... when I was disconnecting the sensor the input that I was reading in the Serial monitor was 0

And wave your hand over the Arduino, or just look at it, or the weather changes from humid to dry and it might change from 0 to some random number.

[nonkapa]

First of all you guys are right about weather and humidity having a effect on the analog input when the pin is in the air. I have great news! I solved the problem! It was a malfuctioning cable. I switched cables and the arduino is reading the sensor just fine now. Thank you everyone for your time and advice!