The NRF24L01+ and RFM69 transceiver communicates with the Arduino board via the SPI interface. It is important to always feed the radios with a stable power source of 3.3V.
Refer to the notes about using a regulator or a coupling-capacitor below.
Wiring the NRF24L01+ Radio
NOTE: The input pins on the NRF24L01+ is 5V tolerant. However, you cannot feed the module with more than 3.3V on VCC. If you use a 5V Arduino you have to use a step-down regulator!
|5VReg -> 3.3V||VCC||Red|
Note: The IRQ is currently not used by the MySensors library so it can be left un-connected. If you are using an Arduino Mega, see this post for instructions.
Wiring the RFM69 Radio
NOTE: The NSS, MOSI and SCK are not 5V tolerant on RFM69. You will need to use a level converter if you're using a 5V Arduino.
Configuring MySensors for RFM69
MySensors is configured to use th NRF24 radio by default. To use RFM69, the following needs to be added before including MySensors.h: (TODO, from https://forum.mysensors.org/topic/5526/rfm69-range-issues/36 )
RFM69 AntennaIMPORTANT: You MUST attach an antenna to the board. Aside from not working without an antenna, transmitters can be damaged if they transmit without an antenna present.
By cutting a wire to the proper length you can create a simple antenna for your RFM69 radio. Depending on the frequency of the radio, the antenna has to be cut to different lengths. Cut the antenna slightly longer to give room to solder it to your board. You can always trim it once soldered.
|Frequency||Length (in)||Length (mm)|
|434 MHz||6.47"||164.7 mm|
|868 MHz||3.22"||82.2 mm|
|915 MHz||3.06"||77.9 mm|
Above antenna length represent 1/4 wave. There is also commercial antennas to buy in proper length.
Connecting a Decoupling-Capacitor
If you experience bad reception or if transmitted data never reaches destination, try adding a decoupling capacitor of 4.7µ - 47µF (the exact size usually doesn't matter) across the radio's 3.3V and GND.
|- side||GND||Marked Black on radio|
|+ side||3.3V||Marked Red on radio|
The side with "< - < - "-marking should be connected to GND
Connecting a Voltage Regulator
NOTE: If you are using the 5V version of Arduino Pro Mini (that lacks the 3.3V regulated output) you'll have to connect a 5V->3.3V regulator between the Arduino and Radio.