I’ve searched high and low for a solution to UART communication on Roving Network’s RN-XV. Mostly I’ve found that a lot of people seem to have the same problem I do. Hook the lines up, try to send a command signal ($$$), get zero response, and inevitably go with setup via ad-hoc.
So what am I missing with this chip? I know it’s 3.3v tolerant, so I’ve got a level shifter (a 4050) and a 7833 to get 3.3v out of my 5 (it actually measures about 3.25, but if I read the specification right, that should be fine, right?). On the communication end, I’m using an FTDI cable 5v. I’ve got my Rx going to the DOUT on the xbee breakout, and my TX going to the DIN. I’ve tried connecting through the “screen” command in OS X as well as using the Terminal built into Arduino (selecting the FTDI cable)
I definitely see communication coming out of the cable (with my oscilloscope). I just get no response from the RN-171. Am I missing something obvious here? Has anyone here had success communicating with an RN-XV over Uart (from a computer I mean…)
Suggestions? Thoughts?
I use the FTDI USB-serial breakout board (from SparkFun), with 3.3 V I/O connected directly to RX and TX on the RN module, and talk to it with TeraTerm on a PC. I’ve had no problems communicating.
Make sure that RX/TX are the right way around, that there is a common ground and that your baud rate is correct. I’ve been told by Roving Networks that the module should be powered up before voltages are present on the RX and TX lines.
As a check you can telnet to the module at port 2000. After emitting HELLO it will respond to “$$$” in the same way as over the UART connection.
Well, I feel a bit foolish, but I found my solution.
Using my 4050 level shifter, I had plugged in my RN-XV DOUT into the output, and the RX line on my FTDI to the input. So the RN-XV was communicating just fine, but I never saw it because the output never made it to the RX line. It was a silly mistake, but one you can make if you’re not paying attention.
It’s a common problem. If you have an o-scope, I would advise looking at the lines once while you have it attached backwards, then fix it and take another look at them. It’s pretty easy to spot swapped serial coms if you’ve seen it before.