XBEE-PRO ADC receiving incorrect data sample

Hi there,

i have set up two XBEE-Pro modules to transmit and receive ADC data.

AD0: 0.771V. (LM34 Temperature sensor )
AD1: floating
VREF: 3.3V

I am receiving:
7E 00 0C 83 50 05 29 00 01 06 00 03 FF 03 FF F7

(Modem: XBP24, Function Set: 802.15.3, Version: 10CD)

Occasionally the AD0 value changes to zero in the received packets so it looks something like this:
(7E 00 xx 83 50 05 29 00 01 06 00 00 00 03 FF xx)

In the past the ADC device was giving me the correct output. I moved on to another part of my project (changed some settings) and now I am receiving this frame.

I have restored the default settings on both devices and set the parameters following: http://www.digi.com/support/kbase/kbaseresultdetl.jsp?kb=180

current settings:

ID 3332
DL 5001
MY 5000
IU 1
IT 1
IR 0

ID 3332
DL 5000
MY 5001
D0 2
D1 2
IT 1
IR 250

Can anyone help me figure out my problem?
I have returned my circuit to a basic setup with:
VCC (pin 1) 3.3V
GND (pin 10) GND
VREF (pin 14) 3.3V

I have also measured using a multimeter at the DIO/ADC pins on the xbee module and I am getting the expected voltage reading.

Is it possible I have somehow destroyed my xbee ADC pins? I However get the correct outputs using DO High and DO Low.

Any help would be very much appreciated.

The checksum on the first frame you quoted should have been F3. Still, as it’s a received frame, I’m guessing that was just a typo.

Have you made sure the pullup resistors on the analog inputs are disabled? If they’re not, that might cause the symptom.

Also worth noting is the need for a decoupling capacitor on any analog input. Without that you’ll get noisy and inaccurate readings. This is the voice of experience - I’m using similar sensors. However, the absence of a capacitor would not cause the problem you’re seeing at the moment.

Sorry - forgot to say this before.

Firmware version 10CD is a bit old. I don’t think that affects your immediate problem, but an upgrade to the latest version might save you from other future problems.

Thanks for your re,

I’m so sorry I left this link for so long, but I was expecting a notification email or something to be sent. So I have assumed no one had replied.

I have thought about the pull up resistors, and adjusted the bits accordingly (used 0x67 to disable PR on D0 and D1. However, it still did not work. I also updated my firmware to 10e8, again this had no effect.

I thought that maybe my 3.3V regulator wasn’t supplying enough current to sample. It supplies a max current of 250mA. I’m using the xbee pro model and the max transmission current is 250mA :s

I’m not to sure if this would have an effect. I thought 250mA would have been just enough. I’ll try a higher rated regulator and let you know how it goes.

What do you think?

The regulator does look marginal, so I reckon that’s a good idea.

As to whether the pins are ok, you could reconfigure to use different pins, or swap the chips. If it still doesn’t work, it’s probably not the pins. I assume it’s unlikely that all pins on both chips could be damaged…

If none of that works, then I’m running out of ideas. But you could try saving the configurations of both chips (using X-CTU) in a pair of .PRO files and posting those. It might give a bit more to work on.