A week ago I got a set of HopeRF Anarduino Mini RFM69HW boards in the mail. These boards are similar to an Arduino Pro Mini but have a RFM69HW wireless module mounted on them. They’re reportedly 100% Arduino IDE compatible and run at 8Mhz. The 6-pin header interconnect is an unpopulated set of six IO interfaces for FTDI type USB to UART (or similar) module or cable. The board also supports all the GPIOs you’d find on a similar Arduino board plus two additional analog pins, A6 and A7. You can see on the image here the FTDI headers and the four GPIO pins I’ll be using.
First things first, I soldered a set of straight male pains on the two GPIO interfaces and a set of 90 degree pins on the FTDI interface. After downloading and installing the RFM69 libraries I was ready to go. Then I connected a SparkFun FTDI 3.3VDC Basic Board to the FTDI interface, plugged in a USB cable and and fired up the Arduino IDE. Worked like a charm.
On the 1.6.4 version of the Arduino IDE you have to select the board, the processor and COM port. Initially I tried the Arduino Mini with no luck. After poking around on the internet I found a recommendation for using an Arduino Pro Mini setting and that did the trick. Once the IDE recognized the board I was able to compile and upload a demo program and soon had the two devices talking across the wireless link. However, as is normally the case with me and new hardware, there was a small problem.
The RSSI was running in the -110db to -115db range; not great if you want any distance at all. As I moved them more than a few feet apart the signal was lost. Like I said, not a good situation. I tried different orientations but they provided only meager success. With more poking around on the Internet I came across information on installing an external antenna. I ended up cutting a section of 24 ga solid core copper wire to 6 and 13/16th inches and soldering it into the antenna connection pint on the board. Wow, did that do the trick! I’ll get some more detailed information on that later. The short version is that it worked.
RSSI climbed to -10db and I was able to move the client node outside the house with no issue. Even at a distance of ~40’ though multiple walls I’m seeing -45db. Next step is adding a TMP102 sensor and battery pack to the setup. More to come.