Prop with RN-XV Issue

msg558

I recently got the RN-XV WiFly module from SparkFun. https://www.sparkfun.com/products/10822

I was able to configure it and access some files on my local FTP server with it using the XBEE usb adapter board. Things went down hill when I tried to interface it with my prop quickstart board. I connected the UART_TX and UART_RX of the module directly to the prop's 0 and 1 pins. The module remained powered with LEDs blinking in this configuration for a few minutes, but then the LED's stopped blinking. The module is now unresponsive when using the usb adapter board as well. Apparently connecting the TX and RX pins directly was a bad choice, but would that be enough to fry the module?

prof_braino

I thought 3.3 v was fine to connect directly to prop pins. We do it all the time using the HC06 bluetooth modules, I do ever stupid mistake possible and havent fried one yet. We only use the 10k resistor thing when connectiong a 5v output to our prop pin input. The rest are just straight wires.


What was the circuit, the code you used?

Mike Green

I use the RN-XV WiFly module regularly, usually on Prop BOE and Prop Activity Boards. I've used them with Parallax's USB Adapter Board and the xBee Adapter Board. You can connect the UART_TX and UART-RX pins of the module directly to Propeller I/O pins although you need to be careful that you've got the I/O pins programmed properly. You don't want the Propeller to be transmitting to the WiFly's transmit pin. That will eventually burn out the WiFly's transmit pin. A 220 Ohm resistor between the WiFly pin and the Propeller I/O pin will protect both from this mistake.

You can't use the 5V/3.3V xBee Adapter directly with the Propeller since this adapter is meant for use with 5V microcontrollers like the Stamps or the Arduino.

msg558

Here's a snapshot of how it was hooked up. The module is just on the xbee adapter board http://www.parallax.com/product/32403. Reviewing my code reveals at least one error. I was trying to communicate with the module using the parallax serial terminal object: pst.StartRxTx(1,0,0,9600) where pin 1 was set as the prop RX pin. In the picture you can see that pin 1 is going to the module's RX pin. So I WAS transmitting to the module's TX pin. I certainly didn't expect this error to damage the module though.

Mike Green

Yeah, that's what it sounds like happened. The Propeller's I/O pins are robust in design and, when tested, seem to be able to tolerate short circuits indefinitely, not so for other chips like the WiFly. When two I/O pins are connected together and one is set high and the other is set low, you have a short circuit between Vdd and Vss. Depending on how the output structures are designed, you might (like on the WiFly) have currents flowing that can melt the transistors involved or, more likely, the interconnects. Some of these high current failures are due to cumulative effects. They're not necessarily instantaneous. That sounds like what happened to you. Best to use the 220 Ohm resistor I mentioned. This will limit the short circuit current to something on the order of 15mA which should be tolerable to pretty much any chip.

msg558

I guess I've been spoiled by the propellor's robustness! I will definitely be using the resistors whenever the new module comes in (it appears my motto is buy, fry, buy again). Thanks for the help!