How can I get negative values from ADC inputs? Xbee series 1

XBee & XBee Gateway XBee - 802.15.4
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1

Hi everybody,

I need help. I have a doubt measuring analog input voltage levels with my Xbee Series 1.
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I want to measure negative voltages providing the negative signal (-1V) into one analog input DIO0 or DIO1 pin at Xbee.
But the only values that I receive from Coordinator Xbee (Rx) with an API frame are “0000” = 0V.
I have realised that Xbee only can measure positive values from 0V-3.3V (Series 1) with Vref=3,3V, but…

Is there some way to measure negative values from a sensor? Maybe with a wave rectifier, a PIC or an op-amp?
> Once I get “positive values” from Xbee how can I distinguish between negatives and positives?
Could you post more details about how to make it possible?
>
> Thank you in advance!

2

Hi,

I will show you what Digi Customer Support says if someone has the same problem:

The best way is you for to use a Clamper circuit that would allow you to shift the ADC voltage within the radios 0 – 1.2V limits.

Sincerely,

Digi RF Technical Support

3

The XBee, AFAIK, can only work with positive voltages.

If you have negative voltages, you might want to consider using an opamp to invert the voltage.

What is your upper limit of voltage? Is this -1 V to 1 V, for example?

A quick google ‘dc voltage shifting’ turns up:

http://forum.allaboutcircuits.com/showthread.php?t=20132