Tyler Weaver / ADXL345

Republished Library, to be refined for use with the SparkFun 9DOF in HARP project.

Dependents:   9Dof_unit_testing

Fork of ADXL345 by James Watanabe

Diff: ADXL345.cpp

Revision:
2:e64d8b9096cd
Parent:
1:45faba962a46
Child:
3:7b83694c7292
--- a/ADXL345.cpp	Fri Oct 07 21:06:14 2011 +0000
+++ b/ADXL345.cpp	Sun Sep 09 15:37:26 2012 +0000
@@ -136,9 +136,12 @@
     char buffer[6];    
     multiByteRead(ADXL345_DATAX0_REG, buffer, 6);
     
-    readings[0] = (int)buffer[1] << 8 | (int)buffer[0];
-    readings[1] = (int)buffer[3] << 8 | (int)buffer[2];
-    readings[2] = (int)buffer[5] << 8 | (int)buffer[4];
+    // Readings are expressed in 16bit 2's complement, so we must first
+    // concatenate two bytes to make a word and sign extend it to obtain
+    // correct negative values.
+    readings[0] = (int)int16_t(uint16_t(buffer[1]) << 8 | buffer[0]);
+    readings[1] = (int)int16_t(uint16_t(buffer[3]) << 8 | buffer[2]);
+    readings[2] = (int)int16_t(uint16_t(buffer[5]) << 8 | buffer[4]);
 
 }