Logo

Several months ago I bought a 434Mhz transmiter and a receiver planed to make a wireless project, but I couldn't manage to make them work. Later on, I gave up for those moudels and find other way, then I found Xbee which has several good features including Analog-to-digital conversion, low power consumsion and free testing and configuration software. I purchesed 2 Xbee ZigBee OEM RF modules but not a development kit, becasue I want to develop on my breadbord. but I found that the Xbee pin is not fit into my breadboard!! Now I understand why there are Xbee Breakout board in electronics stores.

After put those 2 Xbee into my own breakout board, I found that a transparent mode is very easy to use because they don't need any configuration. I just direct connect Data OUT pin to PIC's RX pin and Data IN to PIC's TX pin and provide 3.3V supply for Xbee. They are amazing replace USART hard-wire between 2 PICs.

For this example, I made wireless thermometer by taking adventage of Xbee ADC, convert voltage value form LM34 temperature sensor and send back to host to calculate and display temperature.

First of all, I need to config 2 Xbee, one is a sender and the other is a receiver.

Sender	Receiver
ID = 0x3456 'PAN ID	ID = 0x3456 'PAN ID
MY = 1 'my address	MY = 2 'my address
DL = 2 'destination address	DL = 1 'destsination address
D0 = 2 'D0 is analog	IU = 1 ' I/O output enable
IR = 0x3E8 'sample rate every 1 second	WR ' save configuration
IT = 1 'sample before transmit 1 time
WR 'save configuration

 

To setup those configuration, for those who have an Xbee's development board, you can use X- CTU program config all those parameters. but I don't have a development board, so I wrote a simple program and let PIC config the Xbee. I use my EASYPIC3 with PIC16F877A on board, connect RS232 port to my PC and then connect PIC's TX pin to Xbee's Data IN pin and PIC's RX pin to Xbee's Dataout pin. Program following below into microcontroller, open USART terminal program under Tools, click Connect and then press Reset button to start program. If all responds in UART terminal window are "OK", the Xbee has been configed. Change setting for receiver and redo again with another Xbee.

char buff = 0;

void interrupt(){
if(PIR1.RCIF){
buff = RCREG;
TXREG = buff;
while(!TXSTA.TRMT);
}
}

void Print_str(char *txt){
while(*txt) Usart_Write(*(txt++));
}
void delay100(){
delay_ms(100);
}

void main(){
INTCON.GIE = 1;
INTCON.PEIE = 1;
PIE1.RCIE = 1;
TXSTA.TXEN = 1;

Usart_init(9600); // initail USART

//Code for sender
Usart_Write('X');
delay_ms(1500);
Print_str("+++"); //enter AT command mode
delay_ms(2000);
Print_str("ATID3456"); //PAN ID
Usart_Write(13);
delay100();
Print_str("ATMY1"); //my address 1
Usart_Write(13);
delay100();
Print_str("ATDL2"); //destination address 2
Usart_Write(13);
delay100();
Print_str("ATD02"); //input 0 in analog mode
Usart_Write(13);
delay100();
Print_str("ATIR3E8"); //sample rate 1 second (hex 3E8)
Usart_Write(13);
delay100();
Print_str("ATIT1"); //samples before transmit 1
Usart_Write(13);
delay100();
Print_str("ATWR"); //write settings to firmware
Usart_Write(13);
delay100();

}

//Code for receiver

Usart_Write('X');
delay_ms(1500);
Print_str("+++");
delay_ms(2000);
Print_str("ATID3456"); //PAN ID
Usart_Write(13);
delay100();
Print_str("ATMY02"); //my address 2
Usart_Write(13);
delay100();
Print_str("ATDL01"); //destination address 1
Usart_Write(13);
delay100();
Print_str("ATWR"); //write settings to firmware
Usart_Write(13);
delay100();

Onec both Xbees-- the sender and the receiver, have been configed. Connect LM34 to D0 pin and provide 1.28V reference voltage to Vref pin as figure shown below.

For recceiver, I use my EASYPIC3 board with PIC16F877A @ 8MHz clock. Provide 3.3V for Xbee and connection shown below.

Figure show below is received data.

Data come in framed using API structure, the packet can be break down as:

• 7E Start delimiter.
• 00 0A Length bytes.
• 83 API identifier value byte.
• 00 01 Source address bytes.
• 20 RSSI value byte.
• 00 Option byte.
• 01 Sample quantity byte.
• 02 00 Channel indicator.
• 02 A2 Sample data ADC0
• B4 Check sum.

For this example, the temperature is calculate form byte 12 and 13. And because it's pretty much the same as my previous LM34 project, so I'm not show C code here.

I found a great web site to upgrade Xbee Firmware , that use a few component. I did follow step by step from that site and it work well, so I built one for my own to upgrade and config my Xbee.

The default config of the Xbee is to operate in Transparent mode, the Xbee act as a serial line replacement. By set AP = 1, the Xbee operates in API (Application Programming Interface) mode which is capabillties for networking application.

When operate in API mode, all data entering and leaving the module is contained frame that define operation or event in the module. To perform 16-bit address sending data in API mode, you have to follow frame structure shown below.

The Length is a number of byte of Frame Data not include Checksum byte. Checksum byte can be calculate by 0xFF - sum of all data in Frame Data.

/*
 * Project name:
     Xbee's API frame structure example
 * Copyright:
      Nicholas Sirirak
  * Description:

 * Test configuration:
     MCU:             PIC18F2620
     Dev.Board:       -
     Oscillator:      HS, 16.0000 MHz
     Ext. Modules:    -
     SW:              mikroC PRO V1.65
  * NOTES:

*/
#define _CTS  PORTC.F0
#define _RTS  LATC.F1

#define Delimeter    0x7E    // start dilimeter
#define DH    00             // MSB destination id
 #define DL    01             // LSB destination id
#define TX_request_16   1    //API identifier
 #define Frame_id        0    // frame id

//******************************************************************************
// Performs API packet data
 //******************************************************************************
void API_frame_send(char *str){
      char checksum = 0;
      char count = 0;
      while(*str != 0){
      checksum += *str;              //sum all text
      count++;
     str++;
     }
      checksum += TX_request_16;     //API identifier
      checksum += Frame_id;          //frame id
      checksum += DH;                //MSB destination address
      checksum += DL;                //LSE destination address
      checksum += 1;                 //Option byte
      checksum = 0xFF - checksum;
      
     str -= count;                  //reset pointer
      count += 5;                    //add 5 byte to counter
 
     UART1_write(Delimeter); // Start delimiter
     UART1_write(0);         // MSB length byte
      UART1_write(count);     // LSB length byte, delimiter and check sum is not include
      UART1_write(TX_request_16);    // API identifier
     UART1_write(Frame_id);    // frame id
      UART1_write(DH);    // MSB destination id
     UART1_write(DL);    // LSB destination id
      UART1_write(1);    // option byte
      while(*str != 0){
      UART1_write(*str);
     str++;
     }
      UART1_write(checksum);
     
}
//******************************************************************************
 // MAIN    MAIN     MAIN
//******************************************************************************
void main() {
      TRISB = 0;
      TRISC = 1;
      ADCON1 = 0x0F;   // all digital I/O
      _RTS = 0;
      UART1_init(9600);
     
     while(1){
         API_frame_send("API structure test");
        delay_ms(1000);
      }
}