fix: filtering fake data from ds18b20

Author: Laxilef

DallasTemperature.cpp

@@ -558,6 +558,14 @@ int32_t DallasTemperature::calculateTemperature(const uint8_t* deviceAddress, ui
                        | neg;
     }
 
+    // detect fake data
+    if (deviceAddress[DSROM_FAMILY] == DS18B20MODEL && scratchPad[6] == 0x0C) {
+        if ((scratchPad[0] == 0x50 && scratchPad[1] == 0x05) || 
+            (scratchPad[0] == 0xFF && scratchPad[1] == 0x07)) {
+            return DEVICE_POWER_ON_RESET_RAW;
+        }
+    }
+
   /*
    DS1820 and DS18S20 have a 9-bit temperature register.
 

DallasTemperature.h

@@ -46,6 +46,10 @@
 #define DEVICE_FAULT_SHORTVDD_F -421.599976
 #define DEVICE_FAULT_SHORTVDD_RAW -32256
 
+#define DEVICE_POWER_ON_RESET_C -251
+#define DEVICE_POWER_ON_RESET_F -419.799988
+#define DEVICE_POWER_ON_RESET_RAW -32128
+
 // Configuration Constants
 #define MAX_CONVERSION_TIMEOUT 750
 #define MAX_INITIALIZATION_RETRIES 3

keywords.txt

@@ -85,3 +85,6 @@ DEVICE_FAULT_SHORTGND_RAW	LITERAL1
 DEVICE_FAULT_SHORTVDD_C	LITERAL1
 DEVICE_FAULT_SHORTVDD_F	LITERAL1
 DEVICE_FAULT_SHORTVDD_RAW	LITERAL1
+DEVICE_POWER_ON_RESET_C	LITERAL1
+DEVICE_POWER_ON_RESET_F	LITERAL1
+DEVICE_POWER_ON_RESET_RAW	LITERAL1

test/unit_test_001.cpp

@@ -47,6 +47,10 @@ unittest(test_error_code) {
     assertEqual(DEVICE_FAULT_SHORTVDD_C, -252);
     assertEqualFloat(DEVICE_FAULT_SHORTVDD_F, -421.6, 0.1);
     assertEqual(DEVICE_FAULT_SHORTVDD_RAW, -32256);
+
+    assertEqual(DEVICE_POWER_ON_RESET_C, -251);
+    assertEqualFloat(DEVICE_POWER_ON_RESET_F, -419.8, 0.1);
+    assertEqual(DEVICE_POWER_ON_RESET_RAW, -32128);
 }
 
 // Test basic initialization and functionality of the DallasTemperature library