===== Lessons Learned =====

For the temperature devices, the family code is important. A Family code
of 0x28 is the 18b20 and contains a 12 bit data register with the least 4 bits
indicating digits to the right of the decimal point. The 18s20 with a family code
of 0x10 only has one digit to the right of the decimal point and thus you need to
account for this in temperature conversions.

If you don't allow enough time for the device to convert you will read the default
startup temperature data which is 0x0550 on the DS18b20 and is a default temp of 185 F.
In addition, when a conversion is started using parasitic power, the bus must be held high
with a strong pullup. I have been turning the AVR output driver on for this instance.









===== The Formulas =====

{{info:c.gif|}} 

{{info:f.gif|}}

===== Temperature conversions =====

Fahrenheit to Celsius

C = (F - 32.0) / 1.8\\

Celsius to Fahrenheit\\

F = (C * 1.8) + 32.0\\

===== C source =====

float C_to_F_degrees( float temp )\\
{\\
return( (temp * 1.8) + 32.0 );\\
}\\

float F_to_C_degrees( float temp )\\
{\\
return( (temp - 32.0) / 1.8 );\\
}\\


==== Converting C to F for One Wire ====

unsigned int temperature;\\
float tempf;\\
tempf = 32.0 + (9.0*(float)temperature)/10.0;\\
temperature = tempf + 0.5;                         // integer Fahrenheit\\
\\
**One Wire PH Anderson**\\

LowByte = OneWireInByte(_1W_Pin);\\
HighByte = OneWireInByte(_1W_Pin);\\
TReading = (HighByte << 8) + LowByte;\\
SignBit = TReading & 0x8000;  // test most sig bit\\
if (SignBit) // negative\\
{\\
TReading = (TReading ^ 0xffff) + 1; // 2's comp\\
}\\
Tc_100 = (6 * TReading) + TReading / 4;    // multiply by (100 * 0.0625) or 6.25\\

Whole = Tc_100 / 100;  // separate off the whole and fractional portions\\
Fract = Tc_100 % 100;\\

if (n==0)  // if its the first time, clear the LCD\\
{\\
Serial.print("?f");\\
delay(100);\\
}\\

if (SignBit) // If its negative\\
{\\
Serial.print("-");\\
}\\
Serial.print(Whole);\\
Serial.print(".");\\
if (Fract < 10)\\
{\\
Serial.print("0");\\
}\\
Serial.print(Fract);\\
Serial.print("?n");\\
}\\
delay(5000);      // 5 second delay.  Adjust as necessary\\
}\\