unapproved pull-request by zfields

Author: pythonista

HX711.cpp

@@ -4,7 +4,7 @@
 HX711::HX711(byte dout, byte pd_sck, byte gain) {
 	PD_SCK 	= pd_sck;
 	DOUT 	= dout;
-	
+
 	pinMode(PD_SCK, OUTPUT);
 	pinMode(DOUT, INPUT);
 
@@ -40,26 +40,44 @@ long HX711::read() {
 	// wait for the chip to become ready
 	while (!is_ready());
 
-	byte data[3];
+    unsigned long value = 0;
+    byte data[3] = { 0 };
+    byte filler = 0x00;
 
 	// pulse the clock pin 24 times to read the data
-	for (byte j = 3; j--;) {
-		for (char i = 8; i--;) {
-			digitalWrite(PD_SCK, HIGH);
-			bitWrite(data[j], i, digitalRead(DOUT));
-			digitalWrite(PD_SCK, LOW);
-		}
-	}
+    data[2] = shiftIn(DOUT, PD_SCK, MSBFIRST);
+    data[1] = shiftIn(DOUT, PD_SCK, MSBFIRST);
+    data[0] = shiftIn(DOUT, PD_SCK, MSBFIRST);
 
 	// set the channel and the gain factor for the next reading using the clock pin
-	for (int i = 0; i < GAIN; i++) {
+	for (unsigned int i = 0; i < GAIN; i++) {
 		digitalWrite(PD_SCK, HIGH);
 		digitalWrite(PD_SCK, LOW);
 	}
 
-	data[2] ^= 0x80;
-
-	return ((uint32_t) data[2] << 16) | ((uint32_t) data[1] << 8) | (uint32_t) data[0];
+    // Datasheet indicates the value is returned as a two's complement value
+    // Flip all the bits
+    data[2] = ~data[2];
+    data[1] = ~data[1];
+    data[0] = ~data[0];
+
+    // Replicate the most significant bit to pad out a 32-bit signed integer
+    if ( data[2] & 0x80 ) {
+        filler = 0xFF;
+    } else if ((0x7F == data[2]) && (0xFF == data[1]) && (0xFF == data[0])) {
+        filler = 0xFF;
+    } else {
+        filler = 0x00;
+    }
+
+    // Construct a 32-bit signed integer
+    value = ( static_cast<unsigned long>(filler) << 24
+            | static_cast<unsigned long>(data[2]) << 16
+            | static_cast<unsigned long>(data[1]) << 8
+            | static_cast<unsigned long>(data[0]) );
+
+    // ... and add 1
+    return static_cast<long>(++value);
 }
 
 long HX711::read_average(byte times) {
@@ -93,9 +111,9 @@ void HX711::set_offset(long offset) {
 
 void HX711::power_down() {
 	digitalWrite(PD_SCK, LOW);
-	digitalWrite(PD_SCK, HIGH);	
+	digitalWrite(PD_SCK, HIGH);
 }
 
 void HX711::power_up() {
-	digitalWrite(PD_SCK, LOW);	
-}
+	digitalWrite(PD_SCK, LOW);
+}