With the addition of an #RFM12Pi expansion board, a Raspberry Pi running emoncms can be used as a powerful emonBase base-station to log, process and visualise energy, temperature and other environmental data.
Data can be logged locally to the Raspberry Pi's SD card and/or to a remote emoncms server. Emoncms graphs and dashboards can be served from the Raspberry Pi's web-server.
The RFM12Pi GPIO expansion board enables the Raspberry Pi to receive or transmit data via RFM12B wireless (433/868/915MHz) from other OpenEnergyMonitor modules such an an emonTx energy and temperature monitoring node, or an emonGLCD display. The RFM12Pi expansion board can be purchased from the OpenEnergyMonitor shop
For the new pre-assembled RFM12Pi V2 see new documentation
The RFM12Pi is uses an ATtiny84 microcontroller running a modified version of JeeLabs RF12Demo to receive wireless data via an RFM12B wireless transceiver and transmit data via the Pi's internal serial port
The RFM12Pi board and much of the software is the work of Martin Harizanov. We worked with Martin on the hardware design and emoncms software integration. We owe Martin a big thank you for the effort put into making this solution work well.
| Quantity | Part |
|---|---|
| 1x | ATtiny84 (RF12B firmware preloaded) |
| 2x | 100nF |
| 1x | 5mm LED |
| 2x | 10K (brown, black, orange, gold) |
| 1 x | 100R (brown, black, brown, gold) |
| 1x | RFM12B (433/868 Mhz) |
| 1x | GPIO 6x2 pin header female socket |
| 1x | ISP 3x2 pin header |
The RFM12Pi's Eagle CAD PCB design files, schematic and Arduino based firmware can be downloaded from Martin Harizanov's GitHub
It's recommended you read this guide and familiarise yourself with the steps before you start the build.
Step 1 - Identify Components and Kit Contents
Lay out, and identify, the components from the kit.
Ok, we're ready to start. Here is the PCB:
Step 2 - 10k Resistors
As a general principle we're going to build up from the lowest-profile component. Start with the resistors. Bend each leg of the resistor 90 degrees, right next to the body. The last colour on all of the resistors is brown - it's recommended that you align them all in the same direction and have the brown at the same end. The colours for the 10K resistor are (brown, black, orange, gold).
Step 3 - 100R Resistor
Add the 100R resistor in exactly the same way, its colours are (brown, black, brown, gold)
Step 4 - ATtiny84 DIL Socket
Fit the ATtiny84 DIL Socket as shown in the picture. Note that one end has a small notch in it - this signifies pin 1 and should match up with the notch on the PCB silkscreen. Make sure the socket is fitted flat on the board.
Step 5 - Green LED
Add the green LED. Ensure the long leg (and round edge) are facing the + symbol printed on the board.
Step 6 - RFM12B RF
Place the RFM12BRF module on the pads (observe the orientation - Crystal on the LEFT) and solder each pad to the board.
Step 7 - 100nF Ceramic Capacitors
Add the two 100nF ceramic capacitors one at either end of the board.
Step 8 - 3x2 pin ISP header
Add the 3x2 pin ISP header. Long pins point up, short pins are soldered to the board.
Step 9 - 6x2 pin GPIO header female socket
The GPIO socket needs to go on the bottom of the board.
Step 10 - RF Antenna
Add the Antenna through the bottom-right hole, and solder it in place. The length of the Antenna is dependant on the frequency of your RFM12B module. This is a piece of wire 82mm long for 868MHz and 165mm for 433MHz which will act as a quarter-wave antenna. For more information on the RFM12B see: 1
Step 11 - ATtiny84 Integrated Circuit
Fit the ATtiny84 IC into its socket. Note the spot next to pin 1 and ensure you insert it the right way round.
ICs usually come with their legs pointing slightly outwards. To get them to fit easily into the socket, put the legs flat on a desk and rock the IC slightly to bend the pins inwards - do that to both sides and try to fit it into the socket again.
Step 12 - Relax job done
Turn off your soldering iron and go and have a cup of tea :-)
The ATtiny84 microcontroller should come pre-loaded with the required firmware (RFM12 Demo sketch). If you have obtained a blank ATtiny84 you'll need to upload the rf12 demo firmware to it:
The 'easy' way to do this is to flash the pre compiled hex file onto the ATtiny, this avoids the need to set up the Arduino IDE for an ATtiny, getting the correct Arduino libraries, etc:
- Download the pre compiled RF12 demo .hex file from the firmware folder on Mharizanov's RF12Pi Github Repo
- Power the RF12Pi board with 3.3V, this can be done from the Pi
- If you have an AVR ISP MKII programmer simply connect it to the ISP
header and run the following terminal commend:
$ sudo avrdude -c avrispmkII -p t84 -P usb -e -Uefuse:w:0xFF:m -Uhfuse:w:0xD7:m -Ulfuse:w:0xE2:m -U flash:w:ATtiny84_RF12_Demo.cpp.hex- This avrdude command sets the ATtiny fuses for internal 8Mhz crystal with the BOD disabled and flashes a pre-compiled RF12 Demo sketch
Alternatively you can compile the RF12 Demo sketch yourself using Arduino IDE:
- Setup Arduino 1.x IDE for operation with an ATtiny by following our guide
- Download a modified version (to use software serial on the ATtiny) of JeeLabs RF12 Demo from Mharizanov's RF12Pi Github Repo
- Ensure you have the latest JeeLabs JeeLib Arduino library installed
- Power the RF12Pi board with 3.3V, this can be done from the Pi
- Connect your AVR programmer to the RF12Pi's ISP header and select your programmer in the Arduino IDE tools>Programmer menu
- In the Arduino IDE, select ATtiny84 @ 8Mhz (internal oscillator; BOD disabled) in the Tools>Board menu and click Tools>Burn Bootloader
- You are now ready to upload the RF12 Demo to the ATtiny84 using the Arduino IDE
- Note: if you're having trouble it might be best to go back to basics with the ATtiny on a breadboard and follow this detailed guide to working with an ATtiny.