What is the maximum analog input voltage

I read on someone’s Xbee Project that it’s easy to burn out the analog inputs if the voltage is too high. They said the the max voltage for the analog input is 1.2 volts. Is this correct? I thought the max voltage would be the same as Vcc or about 3.3 volts.


Use VCC as the max input voltage for all pins of the XBee radio. The analog pins have an internal voltage reference of 1.2V however, which is where that number came from. voltage readings above the reference voltage will simply read at maximum. That is of course as long as the voltage isn’t above the Vcc voltage.

@gworle: I really do hesitate before querying a known expert :slight_smile:

Is this right though? The series 2 XBees are said to have a 1.2V reference, but I thought the series 1’s used the VREF pin (and this is a series 1 forum so I’m assuming that’s what Scott216 is asking about). With series 1 it’s common I think to connect VREF to the 3.3V power line, in which case 3.3V corresponds to the maximum reading, not 1.2. I don’t remember any mention of 1.2V in the 802.15.4 product manual and in my own 802.15.4 application I seem to get sensible results by connecting VREF to VCC and calculating on the basis that VREF==VCC.

Looking at the XBee project referenced by Scott216, I reckon that project was using series 2 XBees, and hence the reference there to 1.2V.

Maybe Scott216 could confirm the XBee version?

Quite right, and good catch. The individual in the link was using the ZigBee devices which have the internal 1.2V reference. The 802.15.4 modules, whose forum this is, has an external voltage reference pin, as you have correctly pointed out.

To Scott, johnf is of course correct, and you may want to double check which module you actually have, because they indeed act differently.

In either case however, as long as the voltage isn’t above the Vcc voltage, you won’t damage any of the pins.

I’m using Series 1. I didn’t know about this difference between series 1 and 2.

Thanks for the clarification.