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### Topic: Sensing negative voltage (Read 3549 times)previous topic - next topic

#### SW_guy

##### Dec 16, 2012, 09:30 pm
I have a project that requires sensing voltage over a range of -2 volts to +2 volts.  The voltage will vary from + to - several times per second.  I cannot find that the Arduino analog pins can sense any voltage outside the range of 0 to +5 volts.  Is there any way to sense & measure negative voltage?

Thanks to anyone who can help

#### retrolefty

#1
##### Dec 16, 2012, 09:48 pm

I have a project that requires sensing voltage over a range of -2 volts to +2 volts.  The voltage will vary from + to - several times per second.  I cannot find that the Arduino analog pins can sense any voltage outside the range of 0 to +5 volts.  Is there any way to sense & measure negative voltage?

Thanks to anyone who can help

Not directly. Usually in cases like yours one can use an external op-amp circuit to 'level shift' the -2 to +2 range to a say 0 to 4 volt or 1 to 5 volt range and then just factor out the offset in software.

Lefty

#### winner10920

#2
##### Dec 16, 2012, 10:16 pm
Are you talking about like an analog reading orjust positiveor negative? If the latter then just an optocoupler will work to tell you if you have negative voltage

#### Magician

#3
##### Dec 16, 2012, 10:22 pm
Other option is to connect voltage divider (1:1) between input and +5V. Than negative -2 would be sensed as +1.5V, and +2V as 3.5V.

#### Tom Carpenter

#4
##### Dec 16, 2012, 10:25 pm
Potential divider is the simplest approach. (EDIT: as Magician has said.)
~Tom~

#### mmcp42

#5
##### Dec 16, 2012, 10:56 pm

Other option is to connect voltage divider (1:1) between input and +5V. Than negative -2 would be sensed as +1.5V, and +2V as 3.5V.

very clever solution
there are only 10 types of people
them that understands binary
and them that doesn't

#### Tom Carpenter

#6
##### Dec 16, 2012, 11:21 pmLast Edit: Dec 16, 2012, 11:23 pm by Tom Carpenter Reason: 1
Just for completeness, attached is the proposed circuit.

The two values 'R' are the same, but the exact value depends on what sort of load resistance you can put on your signal. Ideally they should be no more than 32kOhm, which would present 64kOhm to your signal source.
~Tom~

#### MarkT

#7
##### Dec 17, 2012, 02:08 pm

Other option is to connect voltage divider (1:1) between input and +5V. Than negative -2 would be sensed as +1.5V, and +2V as 3.5V.

Well since we don't know the source's impedance this isn't guaranteed to work - some more information about the source of the
+/- 2V signal would be useful.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

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