Dht22

Projects Programming
1

I have the dht22 wired sensor from adafruit conected to digital pin 2. I haven't played with arduino in over a year so any help or guidance from a couple things:
1:
I'm using this sensor so I can activate a relay going to a crock pot. This is where it'll turn on or off at a certain temperature.
2:
I'm using the humidty part to know when I need to open a valve controlled by a servo to control the humidty at a certain percentage.
3:
I have got it working on a LCD 16x2 display temp (f) and humidty. This will be just an extra add on and later I made add a min/max feature.
Also out of question (may need to be in hardware) has any interfaced this small relay off eBay that's already on a pcb?
Can hardly see the pinout on silkscreen (I bought one).

2

Check - Arduino Playground - DHTLib - it supports a DHT22

Make the switchON and switchOFF temperatures two variables, to get some degree of freedom and to prevent fast ON/OFF iterations. Same for humidity

Here a sketch to get started, Temperature is almost coded, DHT.humidity is left as an exercise :wink: just as some other parts...

Succes,
Rob

(not compiled or tested)

#include <dht.h>

dht DHT;

#define DHT22_PIN 2
#define CROCKPOTPIN 8

#define TEMP_HIGH  22
#define TEMP_LOW 20

#define HUMID_HIGH 60
#define HUMID_LOW 20

float minTemp = 100;
float maxTemp = 0;

float minHumid = 100;
float maxHumid = 0;

int crockValue = 0;

void setup()
{
  Serial.begin(115200);
  Serial.println("TEST PROGRAM ");

  pinMode(CROCKPOTPIN, OUTPUT);
}

void loop()
{
  // READ DATA
  int chk = DHT.read22(DHT22_PIN);

  // DO THE MIN/MAX
  minTemp = min(minTemp, DHT.temperature);
  maxTemp = max(maxTemp , DHT.temperature);

  // DISPLAT DATA
  Serial.println(DHT.temperature, 1);

  // CROCKPOT
  if (DHT.temperature > TEMP_HIGH) crockValue = 1;
  else if (DHT.temperature < TEMP_LOW) crockValue = 0;
  digitalWrite(CROCKPOTPIN, crockValue);


  delay(2000);  // DHT's need a delay between readings ...
}
3

Didn't compile correctly... But this does:

#include "DHT.h"
#define DHTTYPE DHT22


#define DHTPIN 2
DHT dht(DHTPIN, DHTTYPE);
#define CROCKPOTPIN 4

#define TEMP_HIGH  22
#define TEMP_LOW 20

#define HUMID_HIGH 60
#define HUMID_LOW 20

float minTemp = 100;
float maxTemp = 0;

float minHumid = 100;
float maxHumid = 0;

int crockValue = 0;

void setup()
{
  Serial.begin(115200);
  Serial.println("TEST PROGRAM ");

  pinMode(CROCKPOTPIN, OUTPUT);
}

void loop()
{
  // READ DATA
int t = dht.readTemperature();
int temperatureF = (t * 9 / 5) +32.5;

  // DO THE MIN/MAX
  minTemp = min(minTemp, t);
  maxTemp = max(maxTemp , t);

  // DISPLAT DATA
  Serial.println(temperatureF);

  // CROCKPOT
  if (t > TEMP_HIGH) crockValue = 1;
  else if (t < TEMP_LOW) crockValue = 0;
  digitalWrite(CROCKPOTPIN, crockValue);


  delay(2000);  // DHT's need a delay between readings ...
}
4

OK!,

If you work in Fahrenheit you might need to initialize the minTemp also in Fahrenheit : 212 iso 100 :slight_smile:

5

How so? I believe standard the library is in Celcius not fahrenheit which I had to calculate to display F
Edit:
Basically the relay which is connected to say pin 4 its HIGH (relay closed) crock pot will be on till about 120ish degrees F. If it goes higher than 120 then the relay will be LOW (relay open).

6

How so? I believe standard the library is in Celcius not fahrenheit which I had to calculate to display F

OK you do the internal math in Celsius and display it ion Fahrenheit. That makes my remark obsolete. I was under the assumption that you would do the math in F My mistake.

If it is only for the displaying part you could move these lines together, combine them in a logical block or better a separate function. That would make it more explicit that only for displaying F is used ..

void displayTemp(int C)
{
  int F = (C * 9 / 5) +32;
  Serial.println(F);
}
7

I was meaning by reading the value of c (hence it's in celcius when on or off). Couldn't I use #define 120 in f not in c by using some math or am I just going to have to calculate it only for displaying ane figure the temp I'd have to set at in c for the relay?

8

You could do the whole sketch in Fahrenheit except the sensorreading. But even for that you could do

int f = (sensor.getTemperature() * 9 / 5) + 32;

#define 120 ==> #define ((120 * 9 /5) + 32) :slight_smile: