diff --git a/lorahandler.go b/lorahandler.go
index eda95b5..b9e3a90 100644
--- a/lorahandler.go
+++ b/lorahandler.go
@@ -217,9 +217,9 @@ func DecodePayload(s string, deveui string, devaddr string, lrrlat float32, lrrl
 func WriteDatapoint(mytime int64, deveui string, devaddr string, v uint8, h uint8, p uint8, w uint16, w1 int32, w2 int32, t int16, lrrlat float32, lrrlon float32, fw_version int32) {
      // wir nehmen humidity als Referenz, wenn diese > 0 ist, dann ist es
      // eine gueltige Messung
-     var vp uint16  // Voltage in %
+     var vp int16  // Voltage in %
      if (h > 0) {
-         vp = uint16(v) - 70
+         vp = int16(v) - 70
          if vp < 0 { 
            vp = 0
          } else if vp > 100 {