Robomotic's Lab

Arduino pro mini + wireless transmitter= good fun!

The previous breakout board I have produced can be used to interface the RFM12b to a controller such as the arduino pro mini. The RFM12b is a single chip, low power, multi-channel FSK transceiver designed for use in applications requiring FCC or ETSI conformance for unlicensed use in the 433, 868 and 915 MHz bands. 
I have 2 versions of the breakout board:

• a version that requires an external whip antenna: a simple wire soldered on the proper pin
• a version that includes a chip antenna (printed on the board): no need for an external wire

Because there are 2 versions of the RFM12b you need to use a wire of the proper length:

• for the 433MHz range @ 1/4 wave = 164.7mm
• for the 868MHz range @ 1/4 wave = 82.2mm
• for the 915MHz range @ 1/4 wave = 77.9mm

In this snapshot I soldered two breadboards with an 868MHz (the red wire) and a 915MHz (the blue wire), they sit nicely on a standard breadboard for prototyping.

Now the boards are powered at 3.3V as well as the Arduino Pro mini, I'm using one with an atmega328. The RFM12b uses the SPI interface of the atmega and we need a software driver to use the module.

There's already some quality software developed at the Jee Labs, so we only need to use the same wiring used in the Jeenode v.4.
To simplify the process I did a simple wiring table:

For the power connection:

This is how it should look like after the wiring (yes a bit messy) but good for your reference.

The next step is check the transmission between a couple of arduino+rfm12b or a jeenode -if you have one-.

What I suggest you to do is to dowlnoad the last RFM12.h library from:

svn co svn://svn.jeelabs.org/jeelabs/trunk/libraries/RF12

Use Arduino IDE version 18 or later, and put the "RF12" inside a "libraries" folder next to your sketches.

Load the sketch called RFdemo on both the arduinos, setup them correctly in the same band, group and send ack or non ack packages. If you see the same numbers coming out on the serial port, that means is working.

Now if you want to give it a go, you can order the boards with or without the radio module and the pin header. When you place the order please specify which frequency you want, the antenna length (default or different sizes) and if you want the header pin.

For today that's all, in the next article I want to show you my other cool board!

Ciao!