no xbee communication on this design

I have been beating my head against a wall all weekend trying to get this circuit to communicate via xbee.

Can anyone see a reason why this would not work? I have put a scope the xbee din pin and I can see data there but I am not receiving anything on my xbee dongle.

I removed the xbees and then connected a wire from pin 3 of the xbee dongle to pin 2 of the xbee header on my board (rx). I then connected the grounds. By this setup I was able to receive data.

It is once I try to do this wirelessly that it does not work....

I tried different firmware versions for the xbee and used the default settings (vis XTCU restore). I have used the latest firmware and tried older versions (like 1084) to see if it is a matter of not setting the firmware up correctly.

I am trying to use the xbees as a direct virtual serial cable.

I offer $20 via paypal to anyone who figures this out for me!!

I am using atmega168 Xbee series 1 Firmware 10C0

I have tried the default (via XTCU restore) settings and also configuring a Coordinator - Enduser pair.

I checked on the receiving xbee that it had power. I am still totally lost as to why this is not working... I have wasted about 16 hours so far!

Com speed?

I tried at 9600 and at 19200

Do I need to tie the reset pin high?

I have confirmed 100% that the issue is totally with my board design and not with the xbees.

Bummer. I hope it's not too difficult to fix the board design.

I have been up all night but can't figure out what the problem is.

I built a second board just to be sure there was not a fault in the first one.

It should be so simple though.... alll the xbee needs is 3.3V and gnd (which it is getting). I am wondering if there is some kind of noise level that is too high and causing the xbee to freak out?

alll the xbee needs is 3.3V and gnd

Well, it also needs something to transmit, and some place to dump what it receives back (Tx and Rx), but your schematic implies that you have those.

You might try attaching an led, with resistor, to the ASSOC line, grounding the other end, to verify that the board is getting power and is functioning.

I have a very simple sketch running that is constantly sending a string of text and checking to see if any characters are received. If it receives a character it turns an led on pin13 on. When I connected the tx/rx points by wire to the xbee dongle on my pc the transmission/reception routing worked (i.e. I kept receiving the proper string and every time I sent characters the led on the arduino clone pin13 would light up).

I have also tried disconnecting the DIN in line on the xbee (via the jumper on my schematic) to see if I just got transmission but got no results.

I have also tried wiring the 4 pins of the xbee directly to the board using discrete wires to try and isolate some problem with headers (i.e. solder bridge I couldn't see etc.)

I am guessing there has to be a layout issue with my pcb that is causing too much noise on the power lines? Maybe the xbee is way more sensitive than I would believe (even though you can see in the schematic that there is adequate filtering).

I am going to try putting a couple of 0.1u caps right on the xbee module between pwr and gnd to see if some extra filtering will help.

I will also attach an led to pin 15 as suggested.

Do you mind sharing the schematic and board files? Perhaps there is something not quite matching between the two. Another set of eyes might help.

Don't mind sharing at all, I want this to be an open source/shared project. What is the best way for me to post them here? Upload to my webpage and link to the files?

Don't mind sharing at all, I want this to be an open source/shared project. What is the best way for me to post them here? Upload to my webpage and link to the files?

I was just measuring the voltage on the reset pin with my DMM and it seems to fluctuating between 0.5 and 2.0V... I have tried tying this pin to 3.3V in case the reset pin was floating but it made no difference (and I think it has internal pullups anyways)

Upload to my webpage and link to the files?

That's the best way.

Here are the files. The first set is the board I had made (with embarassing mistakes… always hurts to rush a design)

This second set is a corrected layout that I will build next:

Just did another test:

I took my xbee module and connected three wires to it: 3.3V, GND, and the DOUT.

I connected these three pins to an arduino: 3.3V, GND and RX and then uploaded the same test code.

This worked without issue (i.e. the xbee connected and received data)

On my pcb I cut the trace to the RX pin so that I could solder the XBEE directly to it in the same way as my arduino test. That meant the only other things I connected were power and gnd yet this did not work!! argh

In the meantime I have been testing all sort of other functionality on my design and it all works (including using the SPI port etc.)

So what does this mean?? Is there something totally wrong with the 3.3V power supply?

Or is there something connected to other pins of the arduino that somehow interferes?

Could it have something to do with the xtal I am using? (I am guessing no since I was able to receive serial via direct wire)

So frustrating!!

finally some good news! I got it to work by bypassing the 3,3V regulator and then using a TO202 one instead. I am not sure why the one I was using was a problem since my meter showed that it was producing 3.3V and the only thing drawing current from it was the xbee (which is fairly low power). The simple solution design wise is to just use the component that works but I still want to know why this was a problem....

woohoo! SOLVED

So this particular 3.3 regulator does not like having 100n caps on the output but it requires a 10uF cap (at least). Without either of those things it won't work at all.