Hi, I have an arduino mega with a signal (0-5v) connected to analogue pin 0, the problem is that signal doesnt have a GND exit, then I have my reading with a lot of noises, how can I solve it?
I read something that I need a pull up resistor, is that true?
Some data: when output signal is 5v it have 25 mA.
The code that I am using is just analogRead(A0)
Regards
What do you have connected to A0?
Do you have a common ground with the device?
Is it an analog or digital signal?
Some kind of GND is needed between the sensor and controller. Else nothing works.
Post a link to that device, mybe aldo a picture.
This is a current 4-20mA to Voltage converter, I supply it with 24v DC (From a external power source) to have a better range to read (If I supply it with 5v from the arduino, I will only have 0 to 3 volts readings (but without noise :D)). This is product link : LINK
Presumably you are connecting VOUT to your Arduino. You also need to connect the Arduino GND to GND on the module.
Doesn't the module convert the 4-20mA signal into a digitial signal?
...R
Connect that DC gnd to controller GND. Then use the range adjuster to yield a maximum of the Vcc used for the controller.
Robin2:
Presumably you are connecting VOUT to your Arduino. You also need to connect the Arduino GND to GND on the module.Doesn't the module convert the 4-20mA signal into a digitial signal?
...R
Railroader:
Connect that DC gnd to controller GND. Then use the range adjuster to yiekd a maximum of the Vcc used for the controller.
If I connect the module GND to both devices at the same time (External power source and arduino), it will not cause any electrical issue?, and for Robin last question, its give me a voltage signal, then is a analogue output.
Thanks a lot.
I already share the external gnd with the arduino gnd, now I dont have noise.
Thanks a lot u guys.
Regards!
I supply it with 24v DC (From a external power source) to have a better range to read (If I supply it with 5v from the arduino, I will only have 0 to 3 volts readings (but without noise).[/quote]If that board is capable of putting-out more than 5V you should have a voltage divider or an over-voltage protection circuit because more than 5V can smoke your Arduino. Although... You are safe without a common ground. 
DVDdoug:
You are safe without a common ground.
Yes, really safe, but no useful readings.
Reading against Vcc is a bad idea with an absolute voltage signal... read against the internal 1.1V reference (so yes, you have to bring down the board's output voltage range to match, and in the process you an get rid of the 24V supply as well).
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