Fix negative temperatures for DHT22 (#16)

danielfaust · winlinvip · commit 3c637975cfbe · 2018-01-02T10:47:50.000+08:00
This commit fixes issue #14 The MSB carries the sign information, which is filtered with `& 0x8000`. If the flag is present, the remainder will get multiplied by `-1`. All the remaining bits contain the value and are filtered with `& 0x7FFF`.
diff --git a/SimpleDHT.cpp b/SimpleDHT.cpp
@@ -202,7 +202,7 @@ int SimpleDHT22::read2(int pin, float* ptemperature, float* phumidity, byte pdat
         memcpy(pdata, data, 40);
     }
     if (ptemperature) {
-        *ptemperature = (float)temperature / 10.0;
+        *ptemperature = (float)((temperature & 0x8000 ? -1 : 1) * (temperature & 0x7FFF)) / 10.0;
     }
     if (phumidity) {
         *phumidity = (float)humidity / 10.0;

Original file line number	Diff line number	Diff line change
`@@ -202,7 +202,7 @@ int SimpleDHT22::read2(int pin, float* ptemperature, float* phumidity, byte pdat`
`202`	`202`	`memcpy(pdata, data, 40);`
`203`	`203`	`}`
`204`	`204`	`if (ptemperature) {`
`205`		`- *ptemperature = (float)temperature / 10.0;`
	`205`	`+ ptemperature = (float)((temperature & 0x8000 ? -1 : 1) (temperature & 0x7FFF)) / 10.0;`
`206`	`206`	`}`
`207`	`207`	`if (phumidity) {`
`208`	`208`	`*phumidity = (float)humidity / 10.0;`