Differences

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--- info:one_wire_temp_conversion [2008/06/23 20:14] – tomgee
+++ info:one_wire_temp_conversion [2008/09/20 11:54] (current) – tomgee
@@ Line 1: / Line 1: @@
+===== 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 =====
@@ Line 9: / Line 36: @@
 F = (C * 1.8) + 32.0\\
-==== C source ====
+===== C source =====
 float C_to_F_degrees( float temp )\\
@@ Line 15: / Line 42: @@
 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 ====
@@ Line 27: / Line 60: @@
 LowByte = OneWireInByte(_1W_Pin);\\
 HighByte = OneWireInByte(_1W_Pin);\\
-TReading = (HighByte << 8) + LowByte;
+TReading = (HighByte << 8) + LowByte;\\
-SignBit = TReading & 0x8000;  // test most sig bit
+SignBit = TReading & 0x8000;  // test most sig bit\\
-if (SignBit) // negative
+if (SignBit) // negative\\
-{
+{\\
-TReading = (TReading ^ 0xffff) + 1; // 2's comp
+TReading = (TReading ^ 0xffff) + 1; // 2's comp\\
-}
+}\\
-Tc_100 = (6 * TReading) + TReading / 4;    // multiply by (100 * 0.0625) or 6.25
+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
+Whole = Tc_100 / 100;  // separate off the whole and fractional portions\\
-Fract = Tc_100 % 100;
+Fract = Tc_100 % 100;\\
-if (n==0)  // if its the first time, clear the LCD
+if (n==0)  // if its the first time, clear the LCD\\
-{
+{\\
-Serial.print("?f");
+Serial.print("?f");\\
-delay(100);
+delay(100);\\
-}
+}\\
-if (SignBit) // If its negative
+if (SignBit) // If its negative\\
-{
+{\\
-Serial.print("-");
+Serial.print("-");\\
-}
+}\\
-Serial.print(Whole);
+Serial.print(Whole);\\
-Serial.print(".");
+Serial.print(".");\\
-if (Fract < 10)
+if (Fract < 10)\\
-{
+{\\
-Serial.print("0");
+Serial.print("0");\\
-}
+}\\
-Serial.print(Fract);
+Serial.print(Fract);\\
-Serial.print("?n");
+Serial.print("?n");\\
-}
+}\\
-delay(5000);      // 5 second delay.  Adjust as necessary
+delay(5000);      // 5 second delay.  Adjust as necessary\\
-}
+}\\