Wednesday, August 27, 2014

RFM12B Radio

The radio part was left out a bit since beginning of the project. I believe in wires in such way that they are more reliable, and also can carry the power for the remote nodes. But the radio is important for future expansions as well. It can be used for remote self-powered PIR sensors, authorization nodes or for data gathering.
Yesterday I have decided to give them a try, because I had two RFM12B at home along with one bought antenna for the main station. Main station is build in metal enclosure and connected to earth that would block the radio waves. I put together one node with ATMega168 and soldered a radio on it. Then the 1/4 wave length antenna made out of single wire:

Wire lengths:

433 1/4 wave = 164.7mm
433 1/2 wave = 329.4mm
433 full wave = 692.7mm

868 1/4 wave = 82.2mm
868 1/2 wave = 164.3mm
868 full wave = 345.5mm

915 1/4 wave = 77.9mm
915 1/2 wave = 155.9mm
915 full wave = 327.8mm

And went for a search for library. I have found this library from LowPowerLab that looked good and suitable to my needs. Radios didn't work out of the box, but I had suspected it because my wiring are not using the ports the library expect. Main Board uses different pin for radio interrupt.

#elif defined(__AVR_ATmega644P__) || defined(__AVR_ATmega1284P__)
  #define RFM_IRQ     10    // PCINT 10 / INT2

Allowing the PINCHG_IRQ instead of attachInterrupt did not work as well. But luckily changing the attachInterrupt form 0 to 2:

  if (nodeID != 0)
    #if defined(__AVR_ATmega644P__) || defined(__AVR_ATmega1284P__)
      attachInterrupt(2, RFM12B::InterruptHandler, LOW);
      attachInterrupt(0, RFM12B::InterruptHandler, LOW);
    #if defined(__AVR_ATmega644P__) || defined(__AVR_ATmega1284P__)

And packets started for flow through. For a short while, or they would go on on the main board, but the Ethernet stopped working. They both work on the SPI and the RTOS has no direct driver for it. A solution  worked fine:

#elif defined(__AVR_ATmega1284P__)
  #warning W5200 for AlarmBoard only!
  inline static void initSS()    { DDRB  |=  _BV(1); };
  inline static void setSS()     { cli(); PORTB &= ~_BV(1); };  // no interrupt while the SPI bus is busy
  inline static void resetSS()   { PORTB |=  _BV(1); sei();};   // no interrupt while the SPI bus is busy

Edit the Arduino Ethernet library file W5100.h so that it doesn’t allow RFM12b to interrupt while the SPI bus is busy handling Wiznet5100. Just add a cli(); and sei();. I will publish the modified libraies to GitHub.

Saturday, August 23, 2014

The project.

Why I have started the project? Simply because I wanted protect my house from burglars.

Some years ago we've started build a house and the idea sparked in me that I can actually create a security and monitoring system my-self. I've been playing with Arduino and Atmega uCPUs and I wanted to use it for some real project. In the house I have put all the wires for PIR sensors, smoke alarms and entry panels. And along with it I've started researching wire and wireless protocols and possibilities. Step by step I've become more and more interested in the idea and the project started.

What it should do? It should replace standard home security alarms, and in future gather statistics from various sensors and do some home automation.

Some of the functions are already there. I have RS485 nodes connected to main board and talking with it over one twisted pair. I have library created that works with the half duplex receiver/transmitter, handles the communication, packets, and is able to detect contention and errors during transmission. Then I have the hardware ready for widely used and reliable RFM12B radio which will be used for cases where wires are not possible or more preferred. There is also Ethernet module working that can serve web pages for communication and configuration.

What is the mission? I must say I'm happy with this project. It is working well and brings me a lot of joy. I went through several version of software, hardware and design and still I'm not discouraged by all the little pitfalls it has brought along. And because I'm reader of hackaday I've decided to enter the TheHackadayPrize and started to post some project news. This just led me into idea that someone else can benefit from my project or better someone can join and add new features or hardware. In the future I will be posting here the project logs, schematic, source code and documentation.