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### Topic: reading a voltage (Read 849 times)previous topic - next topic

##### Oct 07, 2013, 03:50 pm
have a AVR board that is not an arduino

if i send 5v to one of the analogue channels it outputs a voltage in MV

ie  5v = 5000

however if i send it 5v i get 3600   :--   3.6 v

i have also noticed that the board is reading 177 mv when it is ov  (gnd connected to signal)

what am i dong wrong ?

where is my voltage going !

#### johnwasser

#1
##### Oct 07, 2013, 03:54 pm
Sounds like the wiring of your non-Arduino doesn't match the software.  Perhaps you should ask the vendor of the non-Arduino or the person who wrote the software.
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#2
##### Oct 07, 2013, 03:56 pm
What processor does it use? What is Aref set to? Are you using the internal voltage reference?

How are you applying 5v and getting two different readings?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#3
##### Oct 07, 2013, 09:24 pm
hi guys

thanks for your suggestions - it appears the channel is -2..5 to +2.5 volts !

what is the easiest way to read the 5v ? a voltage divider ?

#### johnwasser

#4
##### Oct 08, 2013, 05:30 pm

thanks for your suggestions - it appears the channel is -2..5 to +2.5 volts !
what is the easiest way to read the 5v ? a voltage divider ?

If you can accurately read values between -2.5V and 2.5V you can use two equal resistors (about 10K Ohms) to divide your 5V signal in half.  Connect your signal to one resistor, the other resistor to Ground and both resistors to your analog input 'channel'.
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