Assignment 15: Networking and Communications

I built a radio network using two of my self-made ATtiny44A-boards: the board for Assignment 6: Electronics Design and the one for Assignment 13: Output Devices. Luckily I had added the serial connector for the servo controlling board, even though it was not needed at that time.

Radio module configuration:

I used three Digi International XBEE radio modules. One module is configured with the XCTU program of Digi International as Zigbee Coordinator AT. The PAN ID is arbitrarily chosen, but is the same for all radio modules. The DL Destination Address Low is FFFF for broadcasting.

Coordinator:
 

The other two XBEE modules are configured as Zigbee Router AT. The DH Destination Address High is the SH Serial Number High of the Coordinator, and the DL Destination Address Low is the SL Serial Number Low of the Coordinator. The idea is, that the Coordinator broadcasts to all Router modules, but the Router modules send only to the Coordinator.

Node1:


Node2:


Connections:

The Coordinator is connected to the PC computer using a SparkFun XBee Explorer USB.



The Routers are connected to an Arduino Wireless Shield connected to an Arduino Uno board. These are used only as voltage regulators to power the XBEE modules and the self-made ATtiny44A boards. The ATtiny board for servos has a 5V regulator and is connected to the 7.5 V Vin of the Arduino, where as the Attiny board without regulator is connected to 5V of the Arduino. The serial bus pins from the ATtiny44A boards are connected directly to the Arduino Wireless Shield pins connected to the XBEE module, as can be seen in the photograph below. An extra header is used between the Arduino Uno board and the shield to give access to the serial bus pins.


Application:

The idea of the network is, that the Coordinator transmits the node number and the corresponding node toggles its LED. After that the node transmits back its node number and the state of the LED so that we know it without seeing the LED. Below is an example of the data traffic. The Serial Console of the XCTU program of Digi International was used. The blue symbols are transmitted by the Coordinator, whereas the red symbols are transmitted by the Router nodes and received by the Coordinator. I tested the range of the radio link to be at least 20 m, which is about the width of our Fab Lab.



Software:

The main loop of the Router nodes reads a character from the serial port, checks if the charater is its node number, toggles the LED if the node number is correct, reads the state of the LED pin, and transmits the node number and the state of the LED to serial port.
The code is modified from Neil's hello.bus.45.c. The main loop is shown below.

#define node_id '2'
...
while (1) {
       
        get_char(&serial_pins, serial_pin_in, &chr);
        if (chr == node_id) {                        // is it me?
            PORTB = PORTB ^ 0x04;                    // toggle LED
            if (PORTB & 0x04){                        // put the state of the LED in character
                ledstate = 'T';
            }
            else{
                ledstate = 'F';
            }
           
            put_char(&serial_port, serial_pin_out, node_id);        // send node number
            put_char(&serial_port, serial_pin_out, ledstate);    // send LED state
           
        }
    }


Files:
Node1
Node2

Home