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dewheater.py
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dewheater.py
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#
# dew-heater-control
#
# 2021-10-18 C. Collins created
#
# This code controls a relay which supplies power to a dew heater circuit. It has been tested with a hacked band dew heater (as referenced below) and
# with resistor based circuits too.
#
# A DHT22 or BME280 sensor is used to monitor temperature and humidity. When dew point cut-in set point is reached then the dew heater relay is closed.
# When the cut-out set point is reached the dew heater relay is opened. Both the cut-in and cut-out set points are defined in the configuration file as
# an offset from degrees Celsius of the dew point. This method of temperature control is primitive, but is sufficient for this purpose.
#
#
# The original design was based upon a dew heater like the one at the link below:
#
# https://www.amazon.com/dp/B08LGN222F?psc=1&ref=ppx_yo2_dt_b_product_details
#
#
#
import sys
import signal
import RPi.GPIO as GPIO
import time
import json
import Adafruit_DHT
from meteocalc import dew_point
import smbus2
import bme280
DHT_SENSOR = Adafruit_DHT.DHT22
ON = 1
OFF = 0
FIRST_TIME_ON = -1.0
def sigterm_handler(signo, frame):
print("SIGTERM signal received, forcing dew heater off, exiting.")
dewHeater.off(True)
GPIO.cleanup()
sys.exit(0)
class ConfigClass:
def __init__(self):
self.loadConfig()
GPIO.setmode(GPIO.BCM)
def loadConfig(self):
try:
with open('/home/pi/dewheater/dewheaterconfig.json', 'r') as f:
self.configFile = json.load(f)
print(json.dumps(self.configFile, indent=4, sort_keys=True))
self.debug = self.configFile['debug']
self.dhtPin = self.configFile['dhtPin']
self.sensorType = self.configFile['sensorType']
if (self.sensorType != "BME280" and self.sensorType != "DHT22"):
sys.stderr.write("\nInvalid sensor type: %s" % self.sensorType)
raise Exception(1)
self.bmeAddress = self.configFile["bmeAddress"]
self.bmePort = self.configFile["bmePort"]
self.dewHeaterPin = self.configFile['dewHeaterPin']
self.dewHeaterCutinOffset = self.configFile['dewHeaterCutinOffset']
self.dewHeaterCutoutOffset = self.configFile['dewHeaterCutoutOffset']
self.dewHeaterMaxTemp = self.configFile['dewHeaterMaxTemp']
self.dewHeaterMinTemp = self.configFile['dewHeaterMinTemp']
self.dewHeaterMaxTimeOn = self.configFile['dewHeaterMaxTimeOn']
self.dewPtCheckDelay = self.configFile['dewPtCheckDelay']
self.fakeDewPoint = self.configFile['fakeDewPoint']
self.fakeDewPointSamples = self.configFile['fakeDewPointSamples']
self.invertOnOff = self.configFile['invertOnOff']
if (self.invertOnOff):
self.relayOn = GPIO.LOW
self.relayOff = GPIO.HIGH
else:
self.relayOn = GPIO.HIGH
self.relayOff = GPIO.LOW
except:
sys.stderr.flush()
sys.exit("\nError opening or parsing config file, exiting")
f.close()
return (True)
config = ConfigClass()
class DHTClass:
def __init__(self):
GPIO.setup(config.dhtPin, GPIO.IN)
def getData(self):
self.humidity, self.temperature = Adafruit_DHT.read_retry(DHT_SENSOR, config.dhtPin)
return self.humidity, self.temperature
dht = DHTClass()
class BME820Class:
def __init__(self):
self.port = config.bmePort
self.address = int(config.bmeAddress, 0)
self.bus = smbus2.SMBus(config.bmePort)
self.bme_calibration_params = bme280.load_calibration_params(self.bus, self.address)
def getData(self):
data = bme280.sample(self.bus, self.address, self.bme_calibration_params)
self.humidity = data.humidity
self.temperature = data.temperature
return self.humidity, self.temperature
bme = BME820Class()
class ConditionsClass:
def __init__(self):
self.fakeDewPointCounter = 0
self.dewPointMet = False
def update(self):
if (config.sensorType == "BME280"):
self.humidity, self.temperature = bme.getData()
else:
if (config.sensorType == "DHT22"):
self.humidity, self.temperature = dht.getData()
else:
sys.stderr.write("\nInvalid temperature sensor type: %s" % config.sensorType)
return
if self.humidity is not None and self.temperature is not None:
if ((self.temperature >= -40) and (self.temperature <= 150)) and (
(self.humidity >= 0) and (self.humidity <= 100)):
self.temp_actual = self.temperature # set actual temp for use when fakeDewPoint is true
self.dewPoint = dew_point(self.temperature, self.humidity)
if (config.fakeDewPoint):
self.fakeDewPointCounter += 1
if (self.fakeDewPointCounter < config.fakeDewPointSamples):
self.temperature = self.dewPoint.c - 2
else:
config.fakeDewPoint = False # fake done, clear flag
if (self.temperature <= self.dewPoint.c + config.dewHeaterCutinOffset):
self.dewPointMet = True
else:
if (self.temperature >= self.dewPoint.c + config.dewHeaterCutoutOffset):
self.dewPointMet = False
else:
sys.stderr.write("\nError calculating dew point, input out of range:")
sys.stderr.write("\nTemp = %3.1fC" % self.temperature)
sys.stderr.write("\nHumdidity = %3.1f%%\n" % self.humidity)
return
conditions = ConditionsClass()
class DewHeaterClass:
def __init__(self):
GPIO.setup(config.dewHeaterPin, GPIO.OUT)
self.cycleRelay() # cycle the relay just as a start up test, if you dont hear it clicking then it aint working
self.status = OFF
self.off(True) # force off in case left on by previous session
self.minTempOn = False
self.maxTempOff = False
self.temp_actual = 0.0
self.maxTimeOn = False
self.timeOn = FIRST_TIME_ON
self.hoursOn = 0
def on(self, forced=False):
if (forced):
GPIO.output(config.dewHeaterPin, config.relayOn)
self.status = ON
if (self.timeStampOn == FIRST_TIME_ON): self.timeStampOn = time.time()
return
if (self.maxTempOff):
print("Max temp reached, 'on' command ignored")
return
if (self.maxTimeOn):
print("Max time on exceeded, 'on' command ignored")
return
GPIO.output(config.dewHeaterPin, config.relayOn)
self.status = ON
if (self.timeStampOn == FIRST_TIME_ON): self.timeStampOn = time.time()
def off(self, forced=False):
if (forced):
GPIO.output(config.dewHeaterPin, config.relayOff)
self.status = OFF
self.timeStampOn = FIRST_TIME_ON
self.hoursOn = 0.0
return
if (self.minTempOn):
print("Min temp on, 'off' command ignored")
return
GPIO.output(config.dewHeaterPin, config.relayOff)
self.status = OFF
self.timeStampOn = FIRST_TIME_ON
self.hoursOn = 0.0
def cycleRelay(self):
self.status = OFF
GPIO.output(config.dewHeaterPin, config.relayOn)
time.sleep(1)
GPIO.output(config.dewHeaterPin, config.relayOff)
time.sleep(1)
GPIO.output(config.dewHeaterPin, config.relayOn)
time.sleep(1)
GPIO.output(config.dewHeaterPin, config.relayOff)
def checkTemps(self):
conditions.update()
if (conditions.temp_actual > config.dewHeaterMaxTemp): # use temp_actual for when fakeDewPoint is set
self.maxTempOff = True
self.off(True)
print("Max temp exceeded, dew heater turned off")
return ()
else:
if (self.maxTempOff):
self.maxTempOff = False
self.on(False)
if (conditions.temperature < config.dewHeaterMinTemp):
self.minTempOn = True
self.on(False)
return ()
else:
if (self.minTempOn):
self.minTempOn = False
self.off(False)
return
if conditions.dewPointMet:
if (not self.maxTempOff):
self.on(False)
else:
if (not self.minTempOn):
self.off(False)
def checkMaxTimeOn(self):
if (config.dewHeaterMaxTimeOn > 0):
if (dewHeater.status == ON):
self.hoursOn = (time.time() - dewHeater.timeStampOn) / 3600
if (self.hoursOn > config.dewHeaterMaxTimeOn):
self.maxTimeOn = True
self.off(True)
print("Max dew heater on time exceeded, dew heater turned off. Restart service to reset")
dewHeater = DewHeaterClass()
def dispalySatus():
print("====================================================")
print("Sensor Type = %s" % config.sensorType, end='')
print(" Dew heater state = ", end='')
if (dewHeater.status == ON):
print("ON ", end='')
else:
print("OFF ", end='')
print(" invertOnOff = %s" % (config.invertOnOff))
print("Temp = %3.1fC, temp_actual = %3.1fC, Humidity %3.1f%%, Dew Point = %3.1fC" % (
conditions.temperature, conditions.temp_actual, conditions.humidity, conditions.dewPoint.c))
print("Dew Point + cut-in offset = %3.1fC, Dew Point + cut-out offset = %3.1fC" % (
conditions.dewPoint.c + config.dewHeaterCutinOffset, conditions.dewPoint.c + config.dewHeaterCutoutOffset))
print("MinTempOn set point = %3.1fC, MinTempOn = %s" % (config.dewHeaterMinTemp, dewHeater.minTempOn))
print("MaxTempOff set point = %3.1fC, MaxTempOff = %s" % (config.dewHeaterMaxTemp, dewHeater.maxTempOff))
print("MaxTimeOn = %3.2fH, MaxTimeOn met = %s, hoursOn = %3.2fH" % (
config.dewHeaterMaxTimeOn, dewHeater.maxTimeOn, dewHeater.hoursOn))
print("Dew point met = %s, fakeDewPoint = %s, fakeDewPointCounter = %i " % (
conditions.dewPointMet, config.fakeDewPoint, conditions.fakeDewPointCounter))
print("====================================================")
def main():
signal.signal(signal.SIGTERM, sigterm_handler)
while True:
dewHeater.checkTemps()
dewHeater.checkMaxTimeOn()
dispalySatus()
time.sleep(config.dewPtCheckDelay)
if __name__ == "__main__":
main()