Relay + Temp sensor

main

#!/usr/bin/python

import Adafruit_BBIO.GPIO as GPIO
from w1thermsensor import W1ThermSensor
import time, json, thread

TARGETTEMP = 80.0
THRESHOLD = 1.0
READDELAY = 5

DUMPEVERY = 500
DUMPFILE = "readings.json"

relaypin = "P8_10"

sensor = None
limits = {"high": 0.0, "low": 999.0}
readings = []
readingsamount = 0
timestart = time.time()

def setup():
    global sensor
    sensor = W1ThermSensor()
    GPIO.setup(relaypin, GPIO.OUT)
    GPIO.output(relaypin, GPIO.HIGH)  # Turn off relay by default
    with open(DUMPFILE, "w") as f:
        l = "{\"readings\":["
        f.writelines(l)

def teardown():
    import os
    global readings, readingsamount
    timeend = time.time()
    final_report = {"timings": {"start": timestart, "end": timeend}}
    switch_relay(False)
    dump_readings(readings)
    with open(DUMPFILE, "a+") as f:
        # We can't 'natively' create a JSON file that progressively dumps to
        # a file. To do so would mean loading the whole file into memory, and
        # them dumping it to a file once again, defeating the
        # purpose of doing an "append only" file. That's why we build
        # the JSON file manually.
        f.seek(-1, os.SEEK_END)
        f.truncate()  # Remove the last comma introduced by 'dump_readings()'
        f.writelines("], %s}" % (repr(final_report)[1:-1]).replace("'", "\""))
    print "Shutting down. Final temp: %.3f C" % sensor.get_temperature()
    print "Did %i readings" % readingsamount

def switch_relay(setting):
    GPIO.output(relaypin, GPIO.LOW if setting else GPIO.HIGH)

def relay_status():
    return True if GPIO.input(relaypin) == 0 else False

def dump_readings(readings):
    # Protip: It's estimated that 9 days of logging every 2 seconds
    # would take up around 12 GB of storage.
    with open(DUMPFILE, "a+") as f:
        f.writelines("%s," % json.dumps(readings)[1:-1])

def status_report(temp, readings):
    print "Target         | %.3f +/- %.3f" % (TARGETTEMP, THRESHOLD)
    print "Temperature    | %.3f" % temp
    print "Highest/lowest | %.3f  /  %.3f" % (limits["high"], limits["low"])
    print "Readings       | %i" % readingsamount
    print "Relay status   | %s" % ("ON" if relay_status() else "OFF")
    print ""

def main():
    global readings, readingsamount
    while True:
        temp = sensor.get_temperature()
        if temp < (TARGETTEMP - THRESHOLD):
            if not relay_status():
                switch_relay(True)
        #elif temp > (TARGETTEMP + THRESHOLD):
            # Cooling code would go here.
            #if relay_status():
            #    switch_relay(False)
        else:
            # Upper limit is useless without true cooling,
            # so just turn off at tripping point
            if relay_status():
                switch_relay(False)

        if temp > limits.get("high"):
            limits["high"] = temp
        if temp < limits.get("low"):
            limits["low"] = temp

        newread = {"time": time.time(), "temp": temp}
        if len(readings) == 0 or readings[-1].get("temp") != newread.get("temp"):
            readings.append(newread)
        readingsamount += 1

        status_report(temp, readingsamount)

        if len(readings) >= DUMPEVERY:
            print "Dumping to file..."
            thread.start_new_thread(dump_readings, (readings[:],))
            readings = []

        time.sleep(READDELAY)

if __name__ == '__main__':
    try:
        setup()
        main()
    except KeyboardInterrupt:
        #switch_relay(False)
        teardown()
    except Exception as e:
        print "ERROR! Something happened: "
        print e
        teardown()