How can I get negative voltage values from a sensor

XBee & XBee Gateway XBee - 802.15.4
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Hi everybody,

I have a sensor that has a voltage value range from -50mV to 1V connected to an Xbee end device that transmits data into a Coord Xbee. Both are Series 1.

With positive values from 0V to 1V any problem, I can measure from 0V to 3.3V with Vref=3,3V in 3mV steps. 10 bits ADC -> 3,3V/1023=max resolution.

But when I measure negative values all the API frames that I receive show “0000” hex value = 0V measured from DIO0 or DIO1 analog input pins.

So, the question will be: How can I measure negative voltage levels? Maybe with a PIC, wave rectifier or an add-on? How can I do that?

In this case, how can I distinguish between “original-negative” values if all values that I get are positive?

Thanks in advance for the replies!

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Hi,

as I’ve posted before 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