Pointer and integer comparison

Using Arduino Programming Questions
1

I am trying to compare a temperature to a dew point so I can regulate a heater. The temperature is labelled OTA (another is EP) and the dew point ((DHT11.dewPointFast()*1.8+34)), DEC). On compile I get an error stating that I can't compare a pointer to an integer. The location of the issue is near the end of the code. Help?

#include <OneWire.h>
#include <DallasTemperature.h>
#include <LiquidCrystal.h>
#include <dht11.h>
#include <math.h>


LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
dht11 DHT11;

#define ONE_WIRE_BUS 3
#define DHT11PIN 2

OneWire oneWire(ONE_WIRE_BUS);

DallasTemperature sensors(&oneWire);

DeviceAddress OTA={0x28, 0x94, 0xBB, 0x60, 0x03, 0x00, 0x00, 0x38};
DeviceAddress EP={0x28, 0xFE, 0xF6, 0xB6, 0x03, 0x00, 0x00, 0x39};

void setup(void)

{
  sensors.begin();
sensors.setResolution(OTA, 10);
sensors.setResolution(EP, 10);

lcd.begin(16,2);
lcd.clear();

pinMode(5, OUTPUT);
pinMode(6, OUTPUT);
}



void printTemperature(DeviceAddress deviceAddress)
{
float tempC = sensors.getTempC(deviceAddress);
if (tempC == -127.00) {
lcd.print("XX");
} else {
lcd.print((int)(DallasTemperature::toFahrenheit(tempC)));
}
}



void loop(void)

  {
//Serial.println("\n");
int chk = DHT11.read(DHT11PIN);
//Serial.print("Read sensor: ");
switch (chk)
{
case 0: Serial.println("OK"); break;
case -1: Serial.println("Checksum error"); break;
case -2: Serial.println("Time out error"); break;
default: Serial.println("Unknown error"); break;
}
 
delay(1000);


//Lcd display for ambient temp, humidity and dew point on line 1.  Remote temps for OTA and EP on line 2.
lcd.setCursor(0,0);
lcd.print("T");
lcd.print((int)DHT11.fahrenheit(), DEC);
lcd.setCursor(5,0);
lcd.print("H");
lcd.print((int)((float)DHT11.humidity), DEC);
lcd.print("%");
lcd.setCursor(10,0);
lcd.print("Dew");
lcd.print((int)((DHT11.dewPointFast()*1.8+32)), DEC);

sensors.requestTemperatures();
lcd.setCursor(0,1);
lcd.print("OTA ");
printTemperature(OTA);
lcd.print(" ");
lcd.setCursor(9,1);
lcd.print("EP ");
printTemperature(EP);
lcd.print(" ");


//Compare OTA and EP temp to Dew Point Temp.  If the temps are less than 2 degrees above dew point, turn on the heaters on pins 5 and 6
{
if (OTA <= ((int)((DHT11.dewPointFast()*1.8+34)), DEC))
{
  digitalWrite(5, HIGH); //if eyepiece temp is equal to or less than the dew point plus 2 degrees turn pin 5 on
}
else 
{
  digitalWrite(5, LOW); //if eyepiece tep is greater than the dew point plus 2 degrees turn pin 6 off
}
}
{
if (EP <= ((int)((DHT11.dewPointFast()*1.8+34)), DEC)) 
{
  digitalWrite(6, HIGH); //if eyepiece temp is equal to or less than the dew point plus 2 degrees turn pin 6 on
}
else 
{
  digitalWrite(6, LOW); //if eyepiece temp is greater than the dew point plus 2 degrees turn pin 6 off
}
}

delay(1000);

  }
2

The lines:

if (OTA <= ((int)((DHT11.dewPointFast()*1.8+34)), DEC))
...
if (EP <= ((int)((DHT11.dewPointFast()*1.8+34)), DEC))

don't make sense and I think are the cause of the problem. What are you trying to do in those lines? In particular, what is the ", DEC" for?

3

The OTA and EP are the DallasOneWire senors.
The ((DHT11.dewPointFast()*1.8+34)) is the DHT11 dew point calculation I want to compare to, converted to farenheit + 2 degrees.
I converted to integer for the LCD.
Not sure what the 'DEC' is for, but the sample for the DHT11 had it, so I kept it.

Ultimately, I just want to compare OTA/EP to dewPointFast+2 degrees.

4

How do you compare {0x28, 0x94, 0xBB, 0x60, 0x03, 0x00, 0x00, 0x38} to an int?

By the way, DEC is #defined as 10, so that code is just asking if {0x28, 0x94, 0xBB, 0x60, 0x03, 0x00, 0x00, 0x38} <= 10. Since they're both constants, I fail to see how that's useful (assuming it was possible)

5

Where you are getting the dht11 library from? I can't find the definition of dewPointFast in the versions I found.

6

https://www.virtuabotix.com/feed/?p=239 That is where I got the library for the DHT11, it has dewPoint and dewPointFast.

As for the addresses, the code doesn't compare the addresses but the temp returned from the addresses, I think. Earlier in the code I use OTA when calling the information to be printed to the LCD: printTemperature, (OTA); I thought I could use the OTA definition as a comparator definition.

7

As for the addresses, the code doesn't compare the addresses but the temp returned from the addresses, I think.

Think again.

if (OTA <= ((int)((DHT11.dewPointFast()*1.8+34)), DEC))

where DeviceAddress OTA={0x28, 0x94, 0xBB, 0x60, 0x03, 0x00, 0x00, 0x38};

8

mitaccio:
https://www.virtuabotix.com/feed/?p=239 That is where I got the library for the DHT11, it has dewPoint and dewPointFast.

As for the addresses, the code doesn't compare the addresses but the temp returned from the addresses, I think. Earlier in the code I use OTA when calling the information to be printed to the LCD: printTemperature, (OTA); I thought I could use the OTA definition as a comparator definition.

What you need is something like this:

if (eyepieceTemp <= ((int)(DHT11.dewPointFast()*1.8+34))

where eyepieceTemp is a temperature reading in deg F from one of your temp sensors.

9

So how do I define the OTA/EP temps so that I can compare them against the dewPointFast? Can you using my code show me? I am an uber-noob with no formal training and very little experience. Just a cut and paster.

10

Something like: float tempC = sensors.getTempC(deviceAddress); ?

11

I have been working on this for a week now and still haven't been able to resolve this using the above mentioned help. Uber-noob here.
In this line of code if (OTA <= ((DHT11.dewPointFast()*1.8+34))) I need to change the (OTA) to be a reference to the temp already called earlier in the code. I assume it needs to be like this:

if (somethingTemperature (OTA) <= ((DHT11.dewPointFast()*1.8+34)))

but I am not sure what that something should be. Any guidance? Suggestions on better ways to fix this?

12

I need to change the (OTA) to be a reference to the temp already called earlier in the code. I assume it needs to be like this:

Not even close.

Think about what you are trying to do. Think about what this bit of code does:

DHT11.dewPointFast()*1.8+34

It calls a method, dewPointFast(), on an object, DHT11. That method returns a value. That value is multiplied by 1.8. Then, 34 is added to the result.

STORE THAT RESULT IN A VARIABLE!!!!!!

Then, later, when you need to do the same thing, store the result in another variable.

Then, it should be fairly easy to see what to compare to see if a change has occurred.