Merge pull request milesburton#10 from milesburton/master

update to latest version

Author: RobTillaart

DallasTemperature.cpp

@@ -46,13 +46,15 @@ DallasTemperature::DallasTemperature()
 #if REQUIRESALARMS
 	setAlarmHandler(NO_ALARM_HANDLER);
 #endif
+    useExternalPullup = false;
 }
 DallasTemperature::DallasTemperature(OneWire* _oneWire)
 {
 	setOneWire(_oneWire);
 #if REQUIRESALARMS
 	setAlarmHandler(NO_ALARM_HANDLER);
 #endif
+    useExternalPullup = false;
 }
 
 bool DallasTemperature::validFamily(const uint8_t* deviceAddress) {
@@ -68,6 +70,21 @@ bool DallasTemperature::validFamily(const uint8_t* deviceAddress) {
 	}
 }
 
+/*
+ * Constructs DallasTemperature with strong pull-up turned on. Strong pull-up is mandated in DS18B20 datasheet for parasitic
+ * power (2 wires) setup. (https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf, p. 7, section 'Powering the DS18B20').
+ */
+DallasTemperature::DallasTemperature(OneWire* _oneWire, uint8_t _pullupPin) : DallasTemperature(_oneWire){
+    setPullupPin(_pullupPin);
+}
+
+void DallasTemperature::setPullupPin(uint8_t _pullupPin) {
+	useExternalPullup = true;
+	pullupPin = _pullupPin;
+	pinMode(pullupPin, OUTPUT);
+	deactivateExternalPullup();
+}
+
 void DallasTemperature::setOneWire(OneWire* _oneWire) {
 
 	_wire = _oneWire;
@@ -207,9 +224,12 @@ void DallasTemperature::writeScratchPad(const uint8_t* deviceAddress,
 	_wire->write(COPYSCRATCH, parasite);
 	delay(20); // <--- added 20ms delay to allow 10ms long EEPROM write operation (as specified by datasheet)
 
-	if (parasite)
+    if (parasite) {
+		activateExternalPullup();
 		delay(10); // 10ms delay
-	_wire->reset();
+		deactivateExternalPullup();
+	}
+    _wire->reset();
 
 }
 
@@ -407,7 +427,9 @@ void DallasTemperature::blockTillConversionComplete(uint8_t bitResolution) {
 		while (!isConversionComplete() && (millis() - delms < now))
 			;
 	} else {
+        activateExternalPullup();
 		delay(delms);
+        deactivateExternalPullup();
 	}
 
 }
@@ -428,6 +450,16 @@ int16_t DallasTemperature::millisToWaitForConversion(uint8_t bitResolution) {
 
 }
 
+void DallasTemperature::activateExternalPullup() {
+	if(useExternalPullup)
+		digitalWrite(pullupPin, LOW);
+}
+
+void DallasTemperature::deactivateExternalPullup() {
+	if(useExternalPullup)
+		digitalWrite(pullupPin, HIGH);
+}
+
 // sends command for one device to perform a temp conversion by index
 bool DallasTemperature::requestTemperaturesByIndex(uint8_t deviceIndex) {
 

DallasTemperature.h

@@ -44,9 +44,12 @@ class DallasTemperature {
 
 	DallasTemperature();
 	DallasTemperature(OneWire*);
+	DallasTemperature(OneWire*, uint8_t);
 
 	void setOneWire(OneWire*);
 
+    void setPullupPin(uint8_t);
+
 	// initialise bus
 	void begin(void);
 
@@ -132,7 +135,7 @@ class DallasTemperature {
 	// Is a conversion complete on the wire? Only applies to the first sensor on the wire.
 	bool isConversionComplete(void);
 
-	int16_t millisToWaitForConversion(uint8_t);
+    int16_t millisToWaitForConversion(uint8_t);
 
 #if REQUIRESALARMS
 
@@ -215,6 +218,10 @@ class DallasTemperature {
 	// parasite power on or off
 	bool parasite;
 
+	// external pullup
+	bool useExternalPullup;
+	uint8_t pullupPin;
+
 	// used to determine the delay amount needed to allow for the
 	// temperature conversion to take place
 	uint8_t bitResolution;
@@ -242,6 +249,10 @@ class DallasTemperature {
 	// Returns true if all bytes of scratchPad are '\0'
 	bool isAllZeros(const uint8_t* const scratchPad, const size_t length = 9);
 
+    // External pullup control
+    void activateExternalPullup(void);
+    void deactivateExternalPullup(void);
+
 #if REQUIRESALARMS
 
 	// required for alarmSearch

README.md

@@ -16,6 +16,11 @@ You will need a pull-up resistor of about 5 KOhm between the 1-Wire data line
 and your 5V power. If you are using the DS18B20, ground pins 1 and 3. The
 centre pin is the data line '1-wire'.
 
+In case of temperature conversion problems (result is `-85`), strong pull-up setup may be necessary. See section 
+_Powering the DS18B20_ in 
+[DS18B20 datasheet](https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf) (page 7)
+and use `DallasTemperature(OneWire*, uint8_t)` constructor.
+
 We have included a "REQUIRESNEW" and "REQUIRESALARMS" definition. If you 
 want to slim down the code feel free to use either of these by including
 

examples/ExternalPullup/ExternalPullup.ino

@@ -0,0 +1,35 @@
+#include <OneWire.h>
+#include <DallasTemperature.h>
+
+// Data wire is plugged into port 2 on the Arduino, while external pullup P-MOSFET gate into port 3
+#define ONE_WIRE_BUS    2
+#define ONE_WIRE_PULLUP 3
+
+// Setup a oneWire instance to communicate with any OneWire devices (not just Maxim/Dallas temperature ICs)
+OneWire oneWire(ONE_WIRE_BUS);
+
+// Pass our oneWire reference to Dallas Temperature. 
+DallasTemperature sensors(&oneWire, ONE_WIRE_PULLUP);
+
+void setup(void)
+{
+  // start serial port
+  Serial.begin(9600);
+  Serial.println("Dallas Temperature IC Control Library Demo");
+
+  // Start up the library
+  sensors.begin();
+}
+
+void loop(void)
+{ 
+  // call sensors.requestTemperatures() to issue a global temperature 
+  // request to all devices on the bus
+  Serial.print("Requesting temperatures...");
+  sensors.requestTemperatures(); // Send the command to get temperatures
+  Serial.println("DONE");
+  
+ for(int i=0;i<sensors.getDeviceCount();i++) {
+   Serial.println("Temperature for Device "+String(i)+" is: " + String(sensors.getTempCByIndex(i)));
+ } 
+}