I'm working on a wireless sensor network in which I have one coordinator router (API mode 2) connected to a Raspberry Pi 2, 5 or more routers in API mode 2 as well. Each router is connected to an Arduino Uno. The Unos also have different sensors attached to them (temperature, humidity etc). I have to send data from the sensors to the coordinator and process it. I have successfully transferred data using one router and coordinator (just two XBee S2 modules). On the Arduini I'm using Andrew's library https://github.com/andrewrapp/xbee-arduino and on the Pi I'm using a Python-xbee library https://github.com/nioinnovation/python-xbee. For a single router and coordinator my codes are: Arduino Code (Router):
#include <XBee.h>
#include <math.h>
// create the XBee object
XBee xbee = XBee();
int sensor = A5;
uint8_t payload[8] = {0, 0, 0, 0, 0, 0, 0, 0};
// union to convert float to byte string
union u_tag {
uint8_t b[4];
float fval;
} u;
// SH + SL Address of receiving XBee
XBeeAddress64 addr64 = XBeeAddress64(0x0013a200, 0x40DC7C90);
ZBTxRequest zbTx = ZBTxRequest(addr64, payload, sizeof(payload));
ZBTxStatusResponse txStatus = ZBTxStatusResponse();
int statusLed = 13;
int errorLed = 12;
void flashLed(int pin, int times, int wait) {
for (int i = 0; i < times; i++) {
digitalWrite(pin, HIGH);
delay(wait);
digitalWrite(pin, LOW);
if (i + 1 < times) {
delay(wait);
}
}
}
double Thermistor(int RawADC)
{
double Temp;
Temp = log(10000.0 * ((1024.0 / RawADC - 1)));
Temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * Temp * Temp )) * Temp );
Temp = Temp - 273.15; // Convert Kelvin to Celcius
//Temp = (Temp * 9.0)/ 5.0 + 32.0; // Convert Celcius to Fahrenheit
return Temp;
}
void setup() {
pinMode(statusLed, OUTPUT);
pinMode(errorLed, OUTPUT);
Serial.begin(9600);
}
void loop() {
float rawADC = analogRead(sensor);
float t = Thermistor (rawADC);
// check if returns are valid, if they are NaN (not a number) then something went wrong!
if (!isnan(t)) {
// convert temperature into a byte array and copy it into the payload array
u.fval = t;
for (int i=0;i<4;i++){
payload[i]=u.b[i];
}
u.fval = 100.33;
for (int i=0;i<4;i++){
payload[i+4]=u.b[i];
}
xbee.send(zbTx);
flashLed(statusLed, 1, 100); // flash TX indicator
// after sending a tx request, we expect a status response, wait up to half second for the status response
if (xbee.readPacket(500)) {
// got a response!
// should be a znet tx status
if (xbee.getResponse().getApiId() == ZB_TX_STATUS_RESPONSE) {
xbee.getResponse().getZBTxStatusResponse(txStatus);
// get the delivery status, the fifth byte
if (txStatus.getDeliveryStatus() == SUCCESS) {
// success. time to celebrate
flashLed(statusLed, 5, 50);
} else {
// the remote XBee did not receive our packet. is it powered on?
flashLed(errorLed, 3, 500);
}
}
} else if (xbee.getResponse().isError()) {
//nss.print("Error reading packet. Error code: ");
//nss.println(xbee.getResponse().getErrorCode());
} else {
// local XBee did not provide a timely TX Status Response -- should not happen
flashLed(errorLed, 1, 50);
}
}
delay(2000);
}
Raspberry Pi Code (Coordinator):
from xbee import ZigBee
import serial
import struct
import datetime
PORT = '/dev/ttyUSB0'
BAUD_RATE = 9600
def hex(bindata):
return ''.join('%02x' % ord(byte) for byte in bindata)
# Open serial port
ser = serial.Serial(PORT, BAUD_RATE)
# Create API object
xbee = ZigBee(ser,escaped=True)
# Continuously read and print packets
while True:
try:
response = xbee.wait_read_frame()
sa = hex(response['source_addr_long'])
rf = hex(response['rf_data'])
obj = createObject(response)
obj.createPacket()
print ("Temperature: %.2f" % obj.packet['temperature'],
"Humidity: %.2f" % obj.packet['humidity'],
"Source Address: 0x%s" % obj.packet['sourceAddressShort'],
"Timestamp: %s" % obj.packet['timestamp'].isoformat())
except KeyboardInterrupt:
break
ser.close()
class createObject:
def __init__(self, response):
self.sourceAddrLong = hex(response['source_addr_long'])
self.rfData = hex(response['rf_data'])
self.sourceAddrShort = hex(response['source_addr_long'][4:])
self.options = response.pop('options')
self.frameType = response['id']
self.temperature = struct.unpack('f',response['rf_data'][0:4])[0]
self.humidity = struct.unpack('f',response['rf_data'][4:])[0]
self.dataLength = len(response['rf_data'])
self.packet={}
self.dateNow = datetime.datetime.utcnow()
self.packetJson=0
def createPacket(self):
self.packet.update({
'timestamp' : self.dateNow,
'temperature' : self.temperature,
'humidity' : self.humidity,
'dataLength' : self.dataLength,
'sourceAddressLong' : self.sourceAddrLong,
'sourceAddressShort' : self.sourceAddrShort,
'options' : self.options,
'frameType' : self.frameType
})
I have a few questions that I can't find answers to. I have looked almost everywhere but still have some confusions.
1) In the Arduino code, there is a portion of code at the end where it checks for the status response (I did not write the code, found it on the internet). When I set it up, my errorLED connected to pin 12 blinks once and looking into the code it means that the "local XBee did not provide a timely TX Status Response". My question is, do I have to send a response myself from the coordinator in python or is it generated automatically? If I have to do it myself, how would I do it? Because right now, there is not response. My setup works fine as I'm getting correct values on my Pi.
2) When I have more than one router, how would I handle it in the code? Would I keep sending sensor values after every 2 seconds from the arduino and loop through the address on Pi or is there another way that it is done usually? I'm very confused about it.
3) Right now, if I add more routers, they will keep sending out frames with sensor values and the coordinator reads them in a loop. How can I setup the system such that the coordinator sends a signal to each router and asks for the data and then the router replies with the data? Is it possible?
Any help would be really appreciated. Thank you in advance :)
