Daox's diy arduino thermal differential controller

[Daox]

I find it odd that your sensors are so far off. When I tested mine, they were pretty accurate.

[Mikesolar]

You might want to increase the turn on dT to about 6-8C. Turn off can be 4c. The reason is quite simple, the panel will start at a perceived temp but within in few seconds of flow that temp will change, either up or down depending on conditions. With a small dT, the pump will be on and off too often and it will be hard to get a constant flow.

[nkuck]

What I ended up doing is modifying the readings:
Ssensor += analogRead(SsensorPin) / 2.5;
and the temps are where I would expect them to be.

[Daox]

nkuck, I would suggest a static offset to correct things. Say your sensor reading is off by 10F, just add 10 to the Ssensor variable. With the current way you're doing it, it may read normal at the temperatures you're reading, but as you get farther from those temperatures your readings will get farther and farther off.

Here is what I would do:

// read sensor inputs, convert to degrees, and assign to variables
  Counter = 0;
  while(Counter < SensorReadings) {
    Ssensor += analogRead(SsensorPin) / 2;
    Tsensor += analogRead(TsensorPin) / 2;
    Counter++;
    digitalWrite(ledPin, HIGH);
    Delay(250);
    digitalWrite(ledPin, LOW);
    Delay(250);
  }


  // calculate average temp from sensor inputs
  Ssensor = Ssensor / SensorReadings;
  Tsensor = Tsensor / SensorReadings;

  // calibrate sensors
  Ssensor = Ssensor + 10;
  Tsensor = Tsensor + 13;

This is just an example. Replace the 10 and 13 with whatever the readings seem to be off by. This will create a linear offset that won't drift as the temperature varies.

[nkuck]

Good idea. Thank you. Happy New Year.

[nkuck]

Here is my current sketch and most everything is working fine, except:
When I activate the external relay (a Reeed Relay Shield) both the Ssensor and the Tsensor temps rise 10-20 degrees and stay high until the relay disengages. Could there be some internal heat being generated by the load? Doesn't seem like it would be high enough to make a difference. Thanks for all of your support and patience.

// Pins
int SsensorPin = 4; // the pin to read solar panel temperature
int TsensorPin = 5; // the pin to read water tank temperature
int RelayPin = 7; // the pin to control the pump relay
int ledPin = 13; // led pin to verify relay on condition
int vref;

// Variables
int Ssensor = 0; // holds the value from SsensorPin
int SensorOnDiff = 0; // holds the Ssensor value plus on differential (OnDiff)
int SensorOffDiff = 0; // holds the Ssensor value plus off differential (OffDiff)
int Tsensor = 0; // holds the value from TsensorPin
int SensorReadings = 5; // number of sensor readings to take
int Counter = 0; // sensor readings loop counter
int OnDiff = 4; // temp diff that must exist to turn pump on (dec F)
int OffDiff = 2; // temp diff that must exist to turn pump off (deg F)

// initialize the library with the numbers of the interface pins

#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup()
{
pinMode(SsensorPin, INPUT);
pinMode(TsensorPin, INPUT);
pinMode(RelayPin, OUTPUT);
pinMode(ledPin, OUTPUT);

Serial.begin(9600);

digitalWrite(RelayPin, LOW); // turn pump off

// set up the LCD's number of columns and rows:
lcd.begin(16,2);
}
void loop()
{

// read sensor inputs, convert to degrees, and assign to variables
Counter = 0;
while(Counter < SensorReadings)
{
Ssensor += analogRead(SsensorPin) / 2;
delay(50);
Tsensor += analogRead(TsensorPin) / 2;
delay(50);
Counter++;
digitalWrite(ledPin, LOW);
delay(250);
}
// calculate average temp from sensor inputs
//Ssensor = (500.0 * Ssensor / SensorReadings) / 1024;
// Tsensor = (500.0 * Tsensor / SensorReadings) / 1024;

Ssensor = Ssensor / SensorReadings;
Tsensor = Tsensor / SensorReadings;

// calibrate sensors
Ssensor = Ssensor - 15;
Tsensor = Tsensor - 16;

// add temperature difference to Ssensor value
SensorOnDiff = Ssensor - OnDiff;
SensorOffDiff = Ssensor - OffDiff;

// Print temps to the Computer
Serial.print("Solar temp= ");
Serial.println(Ssensor);
Serial.print("Tank temp= ");
Serial.println(Tsensor);

// Print temps to the LCD
// set the cursor to column 0, line 1
// (note: line 1 is the second row, since counting begins with 0):
lcd.setCursor(0, 0);
lcd.print("Solar=");
lcd.print(Ssensor);
delay(50);
lcd.print((char) 223);
lcd.print("F");
lcd.setCursor(12, 0);
lcd.print("Pump");

lcd.setCursor(0, 1);
lcd.print("Tank =");
lcd.print(Tsensor);
delay(50);
lcd.print((char) 223);
lcd.print("F");

// if heat source is warmer than heat sink sensor, enable relay
if (SensorOnDiff > Tsensor)
{
digitalWrite(RelayPin, HIGH);
digitalWrite(ledPin, HIGH);
lcd.setCursor(13, 1);
lcd.print("ON ");
delay(500);
}
// if heat source sensor is cooler than heat sink sensor, disable relay
if (SensorOffDiff < Tsensor) {
digitalWrite(RelayPin, LOW);
digitalWrite(ledPin, LOW);
lcd.setCursor(13, 1);
lcd.print("OFF");
delay(500);
}
}

[Daox]

That sounds like a very odd problem. It also sounds more like a wiring problem. Can you describe your setup and possibly provide a wiring diagram?

[nkuck]

I don't have a drawing worked up, but I'm thinking...is there a possibility that the way I am using the digital pins and analog pins, with the serial and lcd display, that there is a conflict going on? The wiring is OK per the pins that I have selected. Thank you for looking at this.

[SDMCF]

Originally Posted by nkuck

// Pins
int SsensorPin = 4; // the pin to read solar panel temperature
int TsensorPin = 5; // the pin to read water tank temperature

...

// initialize the library with the numbers of the interface pins

#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

I am no expert, but this code looks odd to me. It seems you are using pins 4 and 5 for the sensors and for the LCD.
Have I read that correctly?
If so, are you sure you can do that?
Do you really have it wired up that way?

[nkuck]

That's precisely my question. I am tryi g to use the analog pins 4 & 5 for the temp inputs amd the digitals for the lcd, but I am not sure if I am setting them up properly and calling them correctly. That may be the reason for my weird readings ��