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Transparent mode no comms

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Hi there,
I am having issues with a 900HP unit on a custom board. I cannot get the radio to communicate in transparent mode. The MCU is running at 5v with a level shifter between the RX/TX and Xbee RX/TX. Converts to 3.3v. Also I am only transmitting a hello world Serial dump.
The PCB is a custom board, running an ATMEGA2560 AU MCU. I have checked at the xbee headers I am getting power +3.3v, I have GND, I also have RX and TX (checked with FTDI cable jumpered into pin 2,3 and GND) I can then get the message ("Hello world Serial3") broadcast every 2 seconds (so shouldn't be anywhere near buffer overrun) This is through the FTDI cable and read in minicom. I have disabled flow control ATD6 0 ATD7 0 and am monitoring from another Xbee in minicom. SO in short or all in all. I have power, I have Serial data but I am not seeing this transmit to the partnered radio. The distance is maybe 5cm between units on the bench, there is no source of interference. I have set the units up in XCTU and can transmit back and forth. Connecting through Serial in XCTU and just sending hello world. I can also use Xbee usb bases and see the info in either direction. It leads me to suspect a connection on the PCB BUT I have also used an XBee breakout board jumpered into the PCB power, ground rx and tx. I have swapped rx and tx just in case there has been a cock up on the PCB but no change. My question is this is there something simple I am missing that would account for this? Like I say I can read a Serial message through FTDI cable, I can read power at the headers but still no comms. Also when I issue an ATND command from the monitoring Xbee it finds the other unit and reports its address etc so they are associating and sharing the same basic settings. I'm getting a little confused over what I should test next for this. I think it must be a setting I need to change but I'm not sure where to head to for it.
asked Jun 18, 2016 in RF Solutions and XBee by simonpearce New to the Community (0 points)

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1 Answer

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Sounds like it is a voltage issue with the level circuit. Try picking up a 3V to 5V level shifting circuit from someone like Spark fun electronics and see if that works between them.
answered Jun 20, 2016 by mvut Veteran of the Digi Community (11,445 points)
Thank you MVUT I will try this avenue now. Oddly enough just yesterday I tried to power the Xbee from a seperate power supply on a breadboard and then connect gnd, rx and tx and it worked briefly. I think you're probably right I either have a level shifting issue(we are using a TXB0108 chip to translate levels) where I have damaged the chip or I have a power issue where there is not enough current being supplied. Interestingly, I also tried different power levels on broadcast on lowest setting nothing got through on 2 it transmitted and on 4 it did not. I was thinking this was maybe due to power and a lack of it. I have already had to modify the boards as when we had them done a connection was missed to a 500mA regulator's enable pin, this was to power the xbee, level shift as well as some LED's as indicators. I am thinking that by using the 3.3v regulator for the gps to power everything by soldering on a jumper wire I am overloading the circuit and it it not stable or some such causing it to not have sufficient power to perform all tasks. This might link up well with the level shifter as problem or Xbee not receiving a stable supply? Once again thank you, I will go test and see if I can get this right.
I think you are on the right track.
We're slowly getting there, have amended the boards to run a seperate 1300 mA regulator to supply the Xbee and Level Shift and also the LEDs, these are now being printed and assembled. It was just too reliable using the explorer bases and separate supply. I'm fairly certain it's a power issue. Using the recommended breadboard circuits it all works even using our board as the controller still. It's always a worry I guess when you have to amend boards and remove things make soldered connections etc. Hoping these next revisions will be back within a month and we move on with testing.
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