Return of the Arduino Dehumidifier controller.

My very good friend Oto has a problem.

He's moved into a new house.

He's wanted some space for his lathes & mills etc, which this has.

 After a few weeks, his machines are showing signs of going rusty.... Why is this?

 It's humidity.. after installing a dehumidifier, things have improved dramatically, except his electricity bill...

 It's time for a slightly revised version of the first project I did on this website back in May 2014 (where does the time go??!?)

It's got a similar display, except it's in Czech, but it has an adjustable set point for humidity, and a mode switch to set between auto , whereby it switches on 5 degrees C before the dew point, or manual, where it switches on when the desired humidity set point is reached.

The mode switch is S2 on the diagram below, and S3 is a centre-biassed momentary toggle, which is used to alter the set point up or down.

The set point is stored in E2PROM, and is restored in the event of power failure.

The temperature and humidity is read from a DHT22 sensor, and the dew point calculated.

The dehumidifier is switched on with a suitable rated relay, via T1.

Here's the code:

/* Oto's Simpler Dehumidifier controller Copyright A.G.Doswell May 2017 License: The MIT License (See full license at the bottom of this file) Visit Andydoz.blogspot.com for description and circuit. */ #include <dht.h> dht DHT; #define DHT22_PIN 7 // DHT data connected to pin 7 #include <LiquidCrystal.h> #include <EEPROM.h> LiquidCrystal lcd(12, 11, 5, 4, 3, 2); // define constants & global variables const int rlyPin = 8; //defines pin the relay is connected to. relay is active low boolean confidence = 0; //confidence default boolean mode = true; // True if dew point selected, false if humidity selected const int TimerLength = 1800;// number of seconds in an hour / 2 - this sets the minimum time the dehumidifier will remain on for. int Timer = 0; //timer is off to start const int modeSwPin = 6; const int upPin = 10; const int downPin = 9; int setPointHumidity; // humidity % set point int setPointTimer = 0; int setPointEEPROM; void setup() { lcd.begin(16, 2); // defines the LCD as a 16 x 2 pinMode (rlyPin, OUTPUT); // sets our relay pin digitalWrite (rlyPin, LOW); // sets the relay off for default condition. pinMode (modeSwPin, INPUT_PULLUP); // sets mode switch pin pinMode (upPin, INPUT_PULLUP); // sets up control pin pinMode (downPin, INPUT_PULLUP); // sets down control pin setPointHumidity = EEPROM.read(0); } void loop() { int chk = DHT.read22(DHT22_PIN); // these 4 lines get data from the sensor int dew = dewPointFast(DHT.temperature, DHT.humidity); // calculate dew point in degrees C int temp = (DHT.temperature); int humidity = (DHT.humidity); int dewTrip = dew + 5; // dew point trip 5 degrees before dew point readModeSwitch (); setPointAdjust (); // writes information about the system to the LCD lcd.clear (); lcd.print("Vlhkost:"); // Czech for humidity! lcd.print (humidity); lcd.print("%"); lcd.setCursor(0, 1); lcd.print(temp); lcd.print((char)0xDF); lcd.print("C"); lcd.setCursor(5, 1); lcd.print("Rosa:"); // Czech for dew! lcd.print(dew); lcd.print((char)0xDF); lcd.print("C"); // dew detect loop. If the dewTrip point is reached, start the timer running and set the dewFlag flag if (mode == true) { if ( temp <= dewTrip) { Timer = 1; } if (Timer >= TimerLength) { // If the timer has expired switch the dehumidifier off. Timer = 0; digitalWrite (rlyPin, LOW); } } if (mode == false) { if (humidity >= setPointHumidity) { Timer = 1; } } if (Timer != 0) { // If the timer is running, switch the dehumidifier on , and write On to the lcd. digitalWrite (rlyPin, HIGH); lcd.setCursor (12, 0); lcd.print ("Na"); Timer++; } else { lcd.setCursor (12, 0); lcd.print ("off"); } if (mode == true) { lcd.setCursor(15, 1); lcd.print ("R"); } else { lcd.setCursor(15, 1); lcd.print ("%"); } delay(2000); // we can only get data from the sensor once every 2 seconds. } double dewPointFast(double celsius, double humidity) { double a = 17.271; double b = 237.7; double temp = (a * celsius) / (b + celsius) + log(humidity * 0.01); double Td = (b * temp) / (a - temp); return Td; } void readModeSwitch () { if (digitalRead (modeSwPin) == true) { mode = true; } else { mode = false; } } void setPointAdjust () { if (digitalRead (upPin) == false) { setPointHumidity++; if (setPointHumidity >= 101) { setPointHumidity = 100; } lcd.setCursor (0, 0); lcd.print ("Nastavte vlhkost "); lcd.setCursor (0, 1); lcd.print (" "); lcd.print (setPointHumidity); lcd.print ("% "); delay (200); setPointTimer = 100; } if (digitalRead (downPin) == false) { setPointHumidity--; if (setPointHumidity <= 0 ) { setPointHumidity = 1; } lcd.setCursor (0, 0); lcd.print ("Nastavte vlhkost"); // Czech for "Set Humidity" lcd.setCursor (0, 1); lcd.print (" "); lcd.print (setPointHumidity); lcd.print ("% "); delay (200); setPointTimer = 100; } if (setPointTimer == 0) { // delay return to loop for 5000 operations setPointEEPROM = EEPROM.read(0); if (setPointEEPROM != setPointHumidity) { // if the value changed, write new value to the EEPROM EEPROM.write(0, setPointHumidity); } return; } setPointTimer --; delay (50); setPointAdjust (); } /* Copyright (c) 2017 Andrew Doswell Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute and sublicense copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. Any commercial use is prohibited without prior arrangement. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHOR(S) OR COPYRIGHT HOLDER(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */

... hope Google's translate has done a reasonable job!