Daily Archives: February 19, 2016

I2C Communications between Raspberry Pi and Arduino – Part One

My daughter has a science project for school on bread mold growth. She will need to monitor the temperature, humidity, and light level of 3 separate environments. Being the geeky dad that I am, I decided to make her some data loggers to monitor each environment. I would also like to take this further by connecting to an online IoT site such as adafruit.io to store and graph the data. There are a few options available such as using an Arduino with a Wi-Fi shield to connect to the site and monitor the environment but that is not an elegant solution. What I have opted to do is to use a Raspberry Pi instead and use I2C to communicate to the sensors using ATTiny85 microcontrollers. One of the reasons for this choice was that she will need to monitor the growth with 10 to 30 slices of bread for each environment. With that many slices in one batch,  there could be a considerable variation throughout the area containing the bread so more than one data logger/sensor cluster should be used. I2C is the perfect solution as you may have up to 127 devices connected with just 3 wires.

Use an Arduino Uno R3 to get information from the sensors and verify that the code works correctly.

Step001_bb

Step001_schem

Arduino Code

#include "DHT.h"

#define PIN_DHT 4
#define PIN_PHOTORESISTOR A3
#define PIN_LED 1

#define debugCode 1

#define DHTTYPE DHT11 // DHT 11
//#define DHTTYPE DHT22 // DHT 22 (AM2302), AM2321
//#define DHTTYPE DHT21 // DHT 21 (AM2301)




float humidity = 0;
float temperatureCelsius = 0;
float temperatureFahrenheit = 0;
float heatIndexCelsius = 0;
float heatIndexFahrenheit = 0;
float lightLevelPercent = 0;

int photocellReading = 0;


// Initialize DHT sensor.
// Note that older versions of this library took an optional third parameter to
// tweak the timings for faster processors. This parameter is no longer needed
// as the current DHT reading algorithm adjusts itself to work on faster procs.
DHT dht(PIN_DHT, DHTTYPE);

void setup() {
 pinMode(PIN_DHT, INPUT);
 pinMode(PIN_PHOTORESISTOR, INPUT);
 pinMode(PIN_LED, OUTPUT);

 digitalWrite(PIN_LED, LOW);

 if (debugCode) {
 Serial.begin(9600);
 while (!Serial) {
 ; // wait for serial port to connect. Needed for native USB
 }
 Serial.println("DHTxx test!");
 }
 dht.begin();
}

void loop() {
 // Wait a few seconds between measurements.
 delay(2000);
 digitalWrite(PIN_LED, HIGH);
 ReadDHT();
 ReadLightLevel();
 if (debugCode) {
 PrintDebug();
 }
 digitalWrite(PIN_LED, LOW);
}

void ReadDHT() {
 humidity = 0;
 temperatureCelsius = 0;
 temperatureFahrenheit = 0;
 heatIndexCelsius = 0;
 heatIndexFahrenheit = 0;

 // Reading temperature or humidity takes about 250 milliseconds!
 // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
 humidity = dht.readHumidity();
 // Read temperature as Celsius (the default)
 temperatureCelsius = dht.readTemperature();
 // Read temperature as Fahrenheit (isFahrenheit = true)
 temperatureFahrenheit = dht.readTemperature(true);

 // Check if any reads failed and exit early (to try again).
 if (isnan(humidity) || isnan(temperatureCelsius) || isnan(temperatureFahrenheit)) {
 Serial.println("Failed to read from DHT sensor!");
 return;
 }

 // Compute heat index in Fahrenheit (the default)
 heatIndexFahrenheit = dht.computeHeatIndex(temperatureFahrenheit, humidity);
 // Compute heat index in Celsius (isFahreheit = false)
 heatIndexCelsius = dht.computeHeatIndex(temperatureCelsius, humidity, false);
}

void ReadLightLevel() {
 photocellReading = analogRead(PIN_PHOTORESISTOR);
 lightLevelPercent = ((float)photocellReading / 1023.0) * 100.0;
}

void PrintDebug() {
 Serial.print("Humidity: ");
 Serial.print(humidity);
 Serial.print(" %\t");
 Serial.print("Temperature: ");
 Serial.print(temperatureCelsius);
 Serial.print(" *C ");
 Serial.print(temperatureFahrenheit);
 Serial.print(" *F\t");
 Serial.print("Heat index: ");
 Serial.print(heatIndexCelsius);
 Serial.print(" *C ");
 Serial.print(heatIndexFahrenheit);
 Serial.print(" *F\t");
 Serial.print("Light Level: ");
 Serial.print(photocellReading); // the raw analog reading
 Serial.print("\t");
 Serial.print(lightLevelPercent); // the raw analog reading
 Serial.println(" %");
}

Output

DHTxx test!
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 198	19.35 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 183	17.89 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 182	17.79 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 182	17.79 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 193	18.87 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 194	18.96 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 188	18.38 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 181	17.69 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 178	17.40 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 183	17.89 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 198	19.35 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 189	18.48 %
Humidity: 34.00 %	Temperature: 21.00 *C 69.80 *F	Heat index: 20.04 *C 68.08 *F	Light Level: 187	18.28 %

 

 

Next Step -> Add Raspberry Pi and I2C Communication