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@krhoyt krhoyt/pubnub.ino
Created Dec 2, 2014

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Spark Core to PubNub
// Libraries
#include <math.h>
// Literals
#define THERMISTOR A0
// Constants
// Thermistor computation
const float ANALOG_STEPS = 4095.0;
const float B_THERM = 3977.0;
const float T_THERM = 298.15;
const float RESISTOR = 10000.0;
const float THERMISTOR_OHM = 10000.0;
const float VOLTAGE = 3.3;
// Constants
// PubNub
const char *CHANNEL = "spark_core";
const char *PUB_KEY = "_YOUR_PUBLISH_KEY_";
const char *PUBNUB_URL = "pubsub.pubnub.com";
const char *SECRET_KEY = "_YOUR_SECRET_KEY_";
const char *SUB_KEY = "_YOUR_SUBSCRIBE_KEY_";
const int PUBNUB_PORT = 80;
const int UPDATE_RATE = 5000;
// TCP connection
TCPClient client;
// Buffer for fomatting
char buffer[100];
// Setup
void setup()
{
// Serial output
Serial.begin( 9600 );
}
// Loop
void loop()
{
double temperature = 0.0;
int analog = 0;
// Analog reading
analog = analogRead( THERMISTOR );
// Thermistor reading as celcius
temperature = thermistor( analog );
// Store data in cloud
if( client.connect( PUBNUB_URL, PUBNUB_PORT ) )
{
request( temperature );
wait();
response();
}
// Wait for next sample
delay( UPDATE_RATE );
}
void request( double value )
{
// Buffers for string conversion
char celcius[10];
char farenheit[10];
// Farenheit as character string
sprintf( celcius, "%2.2f", value );
// Convert to celcius as character string
sprintf( farenheit, "%2.2f", value * 1.80 + 32 );
// Message
sprintf(
buffer,
"{\"fahrenheit\":\"%s\",\"celcius\":\"%s\"}",
farenheit,
celcius
);
client.print( "GET /publish/" );
client.print( PUB_KEY );
client.print( "/" );
client.print( SUB_KEY );
client.print( "/" );
client.print( SECRET_KEY );
client.print( "/" );
client.print( CHANNEL );
client.print( "/0/" );
client.print( buffer );
client.print( "?uuid=" );
client.print( millis() );
client.println( " HTTP/1.1" );
client.println( "Host: pubsub.pubnub.com" );
client.println( "User-Agent: Spark Core" );
client.println( "Content-Length: 0" );
client.println();
}
// Response from proxy
void response()
{
char c;
// While there is data to read
while( client.available() )
{
// Get character
c = client.read();
Serial.print( c );
}
client.stop();
}
// Calculate celcius temperature
// For a 10k resistor at 3.3V
// Using a 10k thermistor
double thermistor( int analog )
{
double kelvin = 0.0;
double l_therm = 0.0;
double r_therm = 0.0;
double v_out = 0.0;
// Thermistor calculations
v_out = VOLTAGE * analog / ANALOG_STEPS;
r_therm = ( RESISTOR * VOLTAGE / v_out ) - RESISTOR;
l_therm = log( THERMISTOR_OHM / r_therm );
kelvin = ( T_THERM * B_THERM ) / ( B_THERM - T_THERM * l_therm );
// Celcius value
return kelvin - 273.15;
}
// Wait for a response from proxy
void wait()
{
// Periodically check curl process
while( !client.available() )
{
Serial.println( "Waiting ..." );
delay( 100 );
}
}
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