The python script used to collect XBee Kill-a-Watt data.

wattcher.py

#!/usr/bin/env python
import serial, time, datetime, sys
from xbee import xbee
from socket import socket
import sensorhistory

LOGFILENAME = "powerdatalog.csv"   # where we will store our flatfile data
DEFAULT_CARBON_SERVER = 'localhost'
DEFAULT_CARBON_PORT   = 2003

SERIALPORT = "/dev/serial/by-id/usb-FTDI_TTL232R-3V3_FTGADQ32-if00-port0"    # the com/serial port the XBee is connected to
BAUDRATE = 9600      # the baud rate we talk to the xbee
CURRENTSENSE = 4       # which XBee ADC has current draw data
VOLTSENSE = 0          # which XBee ADC has mains voltage data
MAINSVPP = 170 * 2     # +-170V is what 120Vrms ends up being (= 120*2sqrt(2))
vrefcalibration = [492,  # Calibration for sensor #0
                   491,  # Calibration for sensor #1
                   489,  # Calibration for sensor #2
                   492,  # Calibration for sensor #3
                   501,  # Calibration for sensor #4
                   493]  # etc... approx ((2.4v * (10Ko/14.7Ko)) / 3
CURRENTNORM = 15.5  # conversion to amperes from ADC
NUMWATTDATASAMPLES = 1800 # how many samples to watch in the plot window, 1 hr @ 2s samples

# open up the FTDI serial port to get data transmitted to xbee
ser = serial.Serial(SERIALPORT, BAUDRATE)
try:
    ser.open()
except:
    print "%s was already open!" % (SERIALPORT)

# open our datalogging file
logfile = None
try:
    logfile = open(LOGFILENAME, 'r+')
except IOError:
    # didn't exist yet
    logfile = open(LOGFILENAME, 'w+')
    logfile.write("#Date, time, sensornum, avgWatts\n");
    logfile.flush()

DEBUG = False
if (sys.argv and len(sys.argv) > 1):
    if sys.argv[1] == "-d":
        DEBUG = True

sensorhistories = sensorhistory.SensorHistories(logfile)
print sensorhistories

# the 'main loop' runs once a second or so
def update_graph(idleevent):
    global avgwattdataidx, sensorhistories, DEBUG

    # grab one packet from the xbee, or timeout
    packet = xbee.find_packet(ser)
    if not packet:
        return        # we timedout

    xb = xbee(packet)             # parse the packet
    #print xb.address_16
    if DEBUG:       # for debugging sometimes we only want one
        print xb

    # we'll only store n-1 samples since the first one is usually messed up
    voltagedata = [-1] * (len(xb.analog_samples) - 1)
    ampdata = [-1] * (len(xb.analog_samples ) -1)
    # grab 1 thru n of the ADC readings, referencing the ADC constants
    # and store them in nice little arrays
    for i in range(len(voltagedata)):
        voltagedata[i] = xb.analog_samples[i+1][VOLTSENSE]
        ampdata[i] = xb.analog_samples[i+1][CURRENTSENSE]

    if DEBUG:
        print "ampdata: "+str(ampdata)
        print "voltdata: "+str(voltagedata)
    # get max and min voltage and normalize the curve to '0'
    # to make the graph 'AC coupled' / signed
    min_v = 1024     # XBee ADC is 10 bits, so max value is 1023
    max_v = 0
    for i in range(len(voltagedata)):
        if (min_v > voltagedata[i]):
            min_v = voltagedata[i]
        if (max_v < voltagedata[i]):
            max_v = voltagedata[i]

    # figure out the 'average' of the max and min readings
    avgv = (max_v + min_v) / 2
    # also calculate the peak to peak measurements
    vpp =  max_v-min_v

    for i in range(len(voltagedata)):
        #remove 'dc bias', which we call the average read
        voltagedata[i] -= avgv
        # We know that the mains voltage is 120Vrms = +-170Vpp
        voltagedata[i] = (voltagedata[i] * MAINSVPP) / vpp

    # normalize current readings to amperes
    for i in range(len(ampdata)):
        # VREF is the hardcoded 'DC bias' value, its
        # about 492 but would be nice if we could somehow
        # get this data once in a while maybe using xbeeAPI
        if vrefcalibration[xb.address_16]:
            ampdata[i] -= vrefcalibration[xb.address_16]
        else:
            ampdata[i] -= vrefcalibration[0]
        # the CURRENTNORM is our normalizing constant
        # that converts the ADC reading to Amperes
        ampdata[i] /= CURRENTNORM

    #print "Voltage, in volts: ", voltagedata
    #print "Current, in amps:  ", ampdata

    # calculate instant. watts, by multiplying V*I for each sample point
    wattdata = [0] * len(voltagedata)
    for i in range(len(wattdata)):
        wattdata[i] = voltagedata[i] * ampdata[i]

    # sum up the current drawn over one 1/60hz cycle
    avgamp = 0
    # 16.6 samples per second, one cycle = ~17 samples
    # close enough for govt work :(
    for i in range(17):
        avgamp += abs(ampdata[i])
    avgamp /= 17.0

    # sum up power drawn over one 1/60hz cycle
    avgwatt = 0
    # 16.6 samples per second, one cycle = ~17 samples
    for i in range(17):
        avgwatt += abs(wattdata[i])
    avgwatt /= 17.0


    # Print out our most recent measurements
    print str(xb.address_16)+"\tCurrent draw, in amperes: "+str(avgamp)
    print "\tWatt draw, in VA: "+str(avgwatt)

    if (avgamp > 13):
        return            # hmm, bad data

    # retreive the history for this sensor
    sensorhistory = sensorhistories.find(xb.address_16)

    # add up the delta-watthr used since last reading
    # Figure out how many watt hours were used since last reading
    elapsedseconds = time.time() - sensorhistory.lasttime
    dwatthr = (avgwatt * elapsedseconds) / (60.0 * 60.0)  # 60 seconds in 60 minutes = 1 hr
    sensorhistory.lasttime = time.time()
    print "\t\tWh used in last ",elapsedseconds," seconds: ",dwatthr
    sensorhistory.addwatthr(dwatthr)

    # Determine the minute of the hour (ie 6:42 -> '42')
    currminute = (int(time.time())/60) % 10
    # Figure out if its been five minutes since our last save
    if (((time.time() - sensorhistory.fiveminutetimer) >= 60.0)
        and (currminute % 5 == 0)
        ):
        # Print out debug data, Wh used in last 5 minutes
        avgwattsused = sensorhistory.avgwattover5min()
        print time.strftime("%Y %m %d, %H:%M")+", "+str(sensorhistory.sensornum)+", "+str(sensorhistory.avgwattover5min())+"\n"

        # Lets log it! Seek to the end of our log file
        if logfile:
            logfile.seek(0, 2) # 2 == SEEK_END. ie, go to the end of the file
            logfile.write(time.strftime("%Y %m %d, %H:%M")+", "+
                          str(sensorhistory.sensornum)+", "+
                          str(sensorhistory.avgwattover5min())+"\n")
            logfile.flush()

        sock = socket()
        try:
            sock.connect( (DEFAULT_CARBON_SERVER, DEFAULT_CARBON_PORT) )
        except:
            print "WARNING: Couldn't connect to %(server)s on port %(port)d, is graphite running?" % { 'server':server, 'port':port }

        timestamp = int( time.time() )
        if (sensorhistory.sensornum == 1):
            message = "%s %s %s" % ("wattage.office.watts", sensorhistory.avgwattover5min(), int(time.time()))
            sock.sendall(message + "\n")

        sock.close()

        # Reset our 5 minute timer
        sensorhistory.reset5mintimer()

while True:
    update_graph(None)