Bluetooth Notes

Last Modified: December 29, 2011


The Cogwheel Nixie Driver board includes a Roving Networks RN-41 Module.  This module provides a complete solution to interfacing a microcontroller system with Bluetooth using a common serial port. On the other end of the Bluetooth connection, a viritual serial port on a PC will appear as a standard hardware serial port, making the entire connection behave exactly as if it were a hard-wired serial interface.

This document describes how to operate the Bluetooth module on the Cogwheel Circuitworks Nixie Driver board. For further information refer to the RN41 documentation on

Uploading New Firmware Over Bluetooth

Firmware updates are done with  avr-dude, which is a utility that comes with the arduino software development kits. Under USB, updates are straightforward (explained elsewhere). In the case of Bluetooth the following procedure must be used:

  • Locate the AVR ISP socket pad which is a 6 pin, 2 row set of holes near the bottom center of the board.
  • With the power off, short pins 5 and 6. This is the system reset line (metal tweezers work well)
  • Power-on the board
  • Manually bring up a connection in your bluetooth neighborood (under XP, it is right-mouse->connect SPP)
  • Simultaneously start the avr-dude command and unshort the reset line.

Adding the Bluetooth Module Yourself

When adding the Bluetooth module keep in mind that this is a very tricky part to solder; Using the solder paste and hot-air method, Since there are no legs , there is a tendency for unmelted paste to get underneath the  module and cause shorts. The best methodology I have found is to first wick off all remnants of solder from the PCB pads then clamp the module in place with tweezers and a rubber band.  Apply a very small amount of paste to the pins and reflow using the lowest air flow setting possible. Add more a little paste until a good visual connect is made between the pads and the pins. Now increase the the air-flow to max or near max and heat the bottom of the board underneath the module. This will liquify any paste that is underneath the board. Then quickly go around and apply high air-flow direct heat to the pads.

In addition R21 (TX connection between USB chip and the microcontroller) needs to be removed. R22 (TX connection between the Bluetooth module and the microcontroller) needs to be added

Initializing a Bluetooth Module

If the Bluetooth module is already present on your board the following procedure has already been performed, so all you normall need to do is to follow the procedures to pair your device using the 1234 default pin.  If you added your own module, you must  first pair the device using the normal procedure:

  • Pair the device with your PC using the 1234 pin
  • Create an SPP device on your PC. It should be associated with a serial communications port
  • Power off the board
  • Power on the board and within 10 seconds, connect to that serial communications port using a terminal emulator program set to 57.6 / 8 / N / 1
  • Type $$$, an ? CMD prompt should appear
  • Type SU,57<enter> AOK should appear
  • Type 3 minus signs  - – - <enter> END should appear
  • Power-cycle, and disconnect/reconnect the terminal emulator. You should now be in communication with the board

This project is released under the Creative Commons Attribution Share-alike license  CC-BY-SA.