Merge pull request milesburton#18 from quozl/master

restore support for DS1820. Many thanks to Quozi

Author: milesburton

DallasTemperature.cpp

@@ -175,7 +175,7 @@ void DallasTemperature::writeScratchPad(const uint8_t* deviceAddress, const uint
     _wire->write(WRITESCRATCH);
     _wire->write(scratchPad[HIGH_ALARM_TEMP]); // high alarm temp
     _wire->write(scratchPad[LOW_ALARM_TEMP]); // low alarm temp
-    // DS18S20 does not use the configuration register
+    // DS1820 and DS18S20 have no configuration register
     if (deviceAddress[0] != DS18S20MODEL) _wire->write(scratchPad[CONFIGURATION]); // configuration
     _wire->reset();
     _wire->select(deviceAddress); //<--this line was missing
@@ -218,7 +218,7 @@ bool DallasTemperature::setResolution(const uint8_t* deviceAddress, uint8_t newR
     ScratchPad scratchPad;
     if (isConnected(deviceAddress, scratchPad))
     {
-        // DS18S20 has a fixed 9-bit resolution
+        // DS1820 and DS18S20 have no resolution configuration register
         if (deviceAddress[0] != DS18S20MODEL)
         {
             switch (newResolution)
@@ -254,8 +254,7 @@ uint8_t DallasTemperature::getResolution()
 // returns 0 if device not found
 uint8_t DallasTemperature::getResolution(const uint8_t* deviceAddress)
 {
-    // this model has a fixed resolution of 9 bits but getTemp calculates
-    // a full 12 bits resolution and we need 750ms convert time
+    // DS1820 and DS18S20 have no resolution configuration register
     if (deviceAddress[0] == DS18S20MODEL) return 12;
 
     ScratchPad scratchPad;
@@ -409,39 +408,50 @@ float DallasTemperature::getTempFByIndex(uint8_t deviceIndex)
     return getTempF((uint8_t*)deviceAddress);
 }
 
-// reads scratchpad and returns the raw temperature (12bit)
+// reads scratchpad and returns fixed-point temperature, scaling factor 2^-7
 int16_t DallasTemperature::calculateTemperature(const uint8_t* deviceAddress, uint8_t* scratchPad)
 {
-    int16_t rawTemperature = (((int16_t)scratchPad[TEMP_MSB]) << 8) | scratchPad[TEMP_LSB];
+    int16_t fpTemperature =
+        (((int16_t) scratchPad[TEMP_MSB]) << 11) |
+        (((int16_t) scratchPad[TEMP_LSB]) << 3);
 
-    /*  DS18S20
-    Resolutions greater than 9 bits can be calculated using the data from
-    the temperature, COUNT REMAIN and COUNT PER °C registers in the
-    scratchpad. Note that the COUNT PER °C register is hard-wired to 16
-    (10h). After reading the scratchpad, the TEMP_READ value is obtained
-    by truncating the 0.5°C bit (bit 0) from the temperature data. The
+    /*
+    DS1820 and DS18S20 have a 9-bit temperature register.
+
+    Resolutions greater than 9-bit can be calculated using the data from
+    the temperature, and COUNT REMAIN and COUNT PER °C registers in the
+    scratchpad.  The resolution of the calculation depends on the model.
+
+    While the COUNT PER °C register is hard-wired to 16 (10h) in a
+    DS18S20, it changes with temperature in DS1820.
+
+    After reading the scratchpad, the TEMP_READ value is obtained by
+    truncating the 0.5°C bit (bit 0) from the temperature data. The
     extended resolution temperature can then be calculated using the
     following equation:
 
                                     COUNT_PER_C - COUNT_REMAIN
     TEMPERATURE = TEMP_READ - 0.25 + --------------------------
                                             COUNT_PER_C
 
-    Simplified to integer arithmetic for a 12 bits value:
-
-    TEMPERATURE = ((raw & 0xFFFE) << 3) - 4 + 16 - COUNT_REMAIN
+    Hagai Shatz simplified this to integer arithmetic for a 12 bits
+    value for a DS18S20, and James Cameron added legacy DS1820 support.
 
     See - http://myarduinotoy.blogspot.co.uk/2013/02/12bit-result-from-ds18s20.html
     */
 
     if (deviceAddress[0] == DS18S20MODEL)
-        rawTemperature = ((rawTemperature & 0xFFFE) << 3) + 12 - scratchPad[COUNT_REMAIN];
+        fpTemperature = ((fpTemperature & 0xfff0) << 3) - 16 +
+            (
+                ((scratchPad[COUNT_PER_C] - scratchPad[COUNT_REMAIN]) << 7) /
+                  scratchPad[COUNT_PER_C]
+            );
 
-    return rawTemperature;
+    return fpTemperature;
 }
 
 
-// returns raw temperature in 1/16 degrees C or DEVICE_DISCONNECTED_RAW if the
+// returns temperature in 1/128 degrees C or DEVICE_DISCONNECTED_RAW if the
 // device's scratch pad cannot be read successfully.
 // the numeric value of DEVICE_DISCONNECTED_RAW is defined in
 // DallasTemperature.h. It is a large negative number outside the
@@ -639,22 +649,20 @@ bool DallasTemperature::alarmSearch(uint8_t* newAddr)
     return true;
 }
 
-// returns true if device address has an alarm condition
-// TODO: can this be done with only TEMP_MSB REGISTER (faster)
-//       if ((char) scratchPad[TEMP_MSB] <= (char) scratchPad[LOW_ALARM_TEMP]) return true;
-//       if ((char) scratchPad[TEMP_MSB] >= (char) scratchPad[HIGH_ALARM_TEMP]) return true;
+// returns true if device address might have an alarm condition
+// (only an alarm search can verify this)
 bool DallasTemperature::hasAlarm(const uint8_t* deviceAddress)
 {
     ScratchPad scratchPad;
     if (isConnected(deviceAddress, scratchPad))
     {
-        float temp = calculateTemperature(deviceAddress, scratchPad);
+        char temp = calculateTemperature(deviceAddress, scratchPad) >> 7;
 
         // check low alarm
-        if ((char)temp <= (char)scratchPad[LOW_ALARM_TEMP]) return true;
+        if (temp <= (char)scratchPad[LOW_ALARM_TEMP]) return true;
 
         // check high alarm
-        if ((char)temp >= (char)scratchPad[HIGH_ALARM_TEMP]) return true;
+        if (temp >= (char)scratchPad[HIGH_ALARM_TEMP]) return true;
     }
 
     // no alarm
@@ -712,18 +720,18 @@ float DallasTemperature::rawToCelsius(int16_t raw)
 {
     if (raw <= DEVICE_DISCONNECTED_RAW)
         return DEVICE_DISCONNECTED_C;
-    // C = RAW/16
-    return (float)raw * 0.0625;
+    // C = RAW/128
+    return (float)raw * 0.0078125;
 }
 
 // convert from raw to Fahrenheit
 float DallasTemperature::rawToFahrenheit(int16_t raw)
 {
     if (raw <= DEVICE_DISCONNECTED_RAW)
         return DEVICE_DISCONNECTED_F;
-    // C = RAW/16
-    // F = (C*1.8)+32 = (RAW/16*1.8)+32 = (RAW*0.1125)+32
-    return ((float)raw * 0.1125) + 32;
+    // C = RAW/128
+    // F = (C*1.8)+32 = (RAW/128*1.8)+32 = (RAW*0.0140625)+32
+    return ((float)raw * 0.0140625) + 32;
 }
 
 #if REQUIRESNEW

DallasTemperature.h

@@ -22,7 +22,7 @@
 #include <OneWire.h>
 
 // Model IDs
-#define DS18S20MODEL 0x10
+#define DS18S20MODEL 0x10  // also DS1820
 #define DS18B20MODEL 0x28
 #define DS1822MODEL  0x22
 #define DS1825MODEL  0x3B

README.md

@@ -10,6 +10,7 @@ This library supports the following devices :
 * DS18B20
 * DS18S20 - Please note there appears to be an issue with this series.
 * DS1822
+* DS1820
 
 
 You will need a pull-up resistor of about 5 KOhm between the 1-Wire data line