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Forum Index : Microcontroller and PC projects : analog negative inputs

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devigan
Newbie

Joined: 11/08/2011
Location: Australia
Posts: 26

Posted: 11:45pm 08 Sep 2011

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Hi, any idea on reading plus minus 5 volt input. just wandering how to read negative voltage. Dave

aargee
Senior Member

Joined: 21/08/2008
Location: Australia
Posts: 255

Posted: 12:51am 09 Sep 2011

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If it's on the same ground reference, the easiest thing would be to use an inverting/differential op-amp circuit. Have a Google of it...

For crying out loud, all I wanted to do was flash this blasted LED.

Xiongmao

Regular Member

Joined: 25/08/2011
Location: Australia
Posts: 48

Posted: 07:23am 09 Sep 2011

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And if the grounds are different or you need isolation for other reasons, feed the voltage to a V/F chip and output that through an opto. Count the pulses to determine the voltage.

seco61
Senior Member

Joined: 15/06/2011
Location: Australia
Posts: 205

Posted: 07:31am 09 Sep 2011

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It all depends on your ground reference. If the -5V supply was completely independent of the Maximite, then (with an appropriate voltage divider network) you could connect the negative rail to the Maximite ground and the supply 0V line to the Maximite input. Then just subtract the appropriate amount from the result.

However, if there is any risk of common grounds then using an inverting op-amp as mentioned above is probably the way to go (and you can scale the voltage by using appropriate values in the op-amp circuit).

Regards

Gerard (vk3cg/vk3grs)

devigan
Newbie

Joined: 11/08/2011
Location: Australia
Posts: 26

Posted: 09:05am 09 Sep 2011

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it's independent supply so I need some sort of a voltage divider. Thanks

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