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[Reply #15 on:]

Thanks for help so much Rob !!

The following was the result of the serial monitor after running the sketch..

endTransmission: 2
byte 1: 101
byte 2: 188

endTransmission: 0

Much appreicated
Pete

[Reply #16 on:]

pdf page 4

                    Output (dec) – 1,638 
  Pressure (mbar) = ------------------------- +600
                             30.84

Code:

float toPressure(byte hi, byte lo)
{
  int t = (hi * 256 + lo) & 0x3FFF;  // see pdf, mask 14 bit
 
  float rv = (t - 1638.0) / 30.84 + 600.0;  // (t - 1638.0) * 0.032425422 + 600.0 // faster
  return rv;
}

byte 1: 101 (low?)
byte 2: 188 (high?)
fill in => 1048 seems a reasonable value

[Reply #17 on:]

Again Rob, I really appreciate your time and help !!

I appended and modified the code to the following complete sketch:

Code:

#include "Wire.h"
#define addrs 0x78 // I2C bus address


void setup()
{
Wire.begin();
Serial.begin(9600);
}

void loop()
{
 
   byte lobyte;
   byte hibyte;
   int Press;
     
   Wire.beginTransmission(addrs);
   Wire.write(1);       
   int x = Wire.endTransmission();

   Serial.print("endTransmission: ");
   Serial.println(x, DEC);
     
   Wire.requestFrom(addrs, 2); // contents of your first two registers
   while(Wire.available() < 2 );          // Check for data from slave
   {   
      delay(1000);
      lobyte = Wire.read();       // Read press high byte
      Serial.println(lobyte, DEC);
      hibyte = Wire.read();      // Read press low byte
      Serial.println(hibyte, DEC);
     
      Press = toPressure(hibyte, lobyte);
      Serial.print("Pressure: ");
      Serial.println(Press);
     
      delay(1000);
   }
   
}
   
   
float toPressure(byte hi, byte lo)
{
  int t = (hi * 256 + lo) & 0x3FFF;  // see pdf, mask 14 bit
 
  float rv = (t - 1638.0) / 30.84 + 600.0;  // (t - 1638.0) * 0.032425422 + 600.0 // faster
  return rv;
 
} 

When the sketch Runs as is, i get the following out on the serial monitor:

endTransmission: 2
103
177
Pressure: 956
endTransmission: 0

I have two questions...
1. Why is it when i remove the following lines of code, the serial monitor shows nothing, it seems to me it should have no affect ?

Code:

Serial.print("endTransmission: ");
Serial.println(x, DEC);

2. How do i get it to constantly update and report the Pressure instead of only running once ?

Thanks,
Pete

[Reply #18 on:]

check - http://tronixstuff.wordpress.com/2010/10/20/tutorial-arduino-and-the-i2c-bus/ -


try move the first delay(1000); outside the if and place it instead of the 2 print statements.

[Reply #19 on:]

Thanks a lot for your Help Rob, everything worked well and i am learning a lot

At this point i need to incorporate this sensor as well,
http://www.smartec-sensors.com/assets/files/pdf/manuals/SMTH08INv2.2.pdf
http://www.sensorguys.com/pdfs/SMTH08IN.pdf

How do i incorporate both sensors considering they use 3.3V & 5V I2C Systems ?

The datasheet is rather confusing to me, how do i read this sensor, do i need to initiate a "conversion" first ?

Some general help and or skeleton code would be appreciated.

Pete

[Reply #20 on:]

sparkfun or farnell sell 5V - 3.3V convertors for I2C. That should be the first step.
Then you can see if the I2C scanner on the playground sees it address.
Third step is checking if you can read the config registers.
(I have no time to dive into the datasheet now, sorry)

[Reply #21 on:]

OK a quick look than,
the protocol looks not too difficult, If I am correct you need to request 4 bytes and do some math on them.

It can be done quite similar as the other sensor, something like below.

(partial concept code)

Code:

Wire.requestFrom(addrs, 4); // contents of your first two registers
   while(Wire.available() < 4 );          // Check for data from slave
   {   
      delay(1000);
      lobyte = Wire.read();       // Read press high byte
      Serial.println(lobyte, DEC);
      hibyte = Wire.read();      // Read press low byte
      Serial.println(hibyte, DEC);
     
      Temp= toTemperature(hibyte, lobyte);
      Serial.print("Temperature: ");
      Serial.println(Temp);

      lobyte = Wire.read();       // Read press high byte
      Serial.println(lobyte, DEC);
      hibyte = Wire.read();      // Read press low byte
      Serial.println(hibyte, DEC);
     
      Hum = toHumidity(hibyte, lobyte);
      Serial.print("Humidity: ");
      Serial.println(Hum);     
      delay(1000);
   }

Now it is your turn

[Reply #22 on:]

check the datasheet for timing (5 seconds), humidity readers need multiple seconds between readings. (DHT series have 2 seconds, but seem not as accurate)