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### Topic: Arduino 50 Hz sine wave Analog read problem (Read 6670 times)previous topic - next topic

#### Achira

##### Sep 25, 2014, 05:50 am
HI,

I use arduino to read a sensor (Antenna) value. we measure from a oscilloscope that antenna values. we got that the maximum value or peak value is some what 200 mV. But the analog read value gives 1023 read as peak. when i give 5 v to the that pin then it gives 1023 also. what is the problem. Can you help me?
Here i attached the arduino readings and the screen shot of the oscilloscope.

#### Achira

#1
##### Sep 25, 2014, 06:02 amLast Edit: Sep 25, 2014, 08:46 pm by robtillaart Reason: 1
hi,
can you help me with this?

this signal is 50 Hz.

I use arduino to read a sensor (Antenna) value. we measure from a oscilloscope that antenna values. we got that the maximum value or peak value is some what 200 mV. But the analog read value gives 1023 read as peak. when i give 5 v to the that pin then it gives 1023 also. what is the problem. Can you help me?
Here i attached the arduino readings and the screen shot of the oscilloscope.

#### Grumpy_Mike

#2
##### Sep 25, 2014, 10:56 am
Quote
But the analog read value gives 1023 read as peak. when i give 5 v to the that pin then it gives 1023 also. what is the problem.

The problem is how you have wired it up. You need to post a schematic.

#### robtillaart

#3
##### Sep 25, 2014, 08:47 pm
moderator:

thank you.
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#### mrburnette

#4
##### Sep 27, 2014, 02:01 amLast Edit: Sep 29, 2014, 02:18 pm by mrburnette Reason: 1

...
this signal is 50 Hz.
as peak. when i give 5 v to the that pin then it gives 1023 also. what is the problem. Can you help me?
Here i attached the arduino readings and the screen shot of the oscilloscope.

http://www.eetimes.com/author.asp?section_id=36&doc_id=1319495

You are misunderstanding what you are measuring w/ the o'scope.
You are simply measuring the power-line 50Hz inducement into the open wire connected to a probe with a 1 megaOhm typical AC/DC impedance.
W/Arduino, the AC hum inducement will be based upon the ADC characteristic DC impedance of approx 100 megaOhm.  But, Atmel indicates that a DC impedance of 10 kiloOhm is desired for accurate ADC measurements:
Quote
(23.6.1) Page 257 states: "The ADC is optimized for analog signals with an output impedance of approximately 10 k? or less. If such a source is used, the sampling time will be negligible. "

Then there is the whole issue that on the Arduino, you can only measure positive voltage, so the input signal must " ride" a bias voltage to allow the +/- nature of the AC to be DC offset.

So, in American lingo, you are comparing Apples to Oranges.

Ray

#### KenF

#5
##### Sep 29, 2014, 12:25 pm
Your problem would be more obvious if you attached a speaker instead of an oscilloscope.  Mains hum is very distinctive

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