add optional diff-temp to dewpoint fan

git-svn-id: https://fhem.svn.sourceforge.net/svnroot/fhem/trunk/fhem@1877 2b470e98-0d58-463d-a4d8-8e2adae1ed80

docs/commandref.html

@@ -1442,6 +1442,7 @@ A line ending with \ will be concatenated with the next one, so long lines
     &lt;regexp&gt;.<br><br>
 
   </ul>
+
   <br>
 
   <a name="Calendarattr"></a>
@@ -6962,6 +6963,7 @@ The one byte hex string is generated by the Oregon sensor when is it powered on.
   <a name="OREGONset"></a>
   <b>Set</b> <ul>N/A</ul><br>
 
+
   <a name="OREGONget"></a>
   <b>Get</b> <ul>N/A</ul><br>
 
@@ -10184,15 +10186,15 @@ KlikAanKlikUit, NEXA, CHACON, HomeEasy UK. <br> You need to define an RFXtrx433
   </ul>
 
   <ul>
-    <code>define &lt;name&gt; dewpoint fan &lt;devicename-regex&gt; &lt;devicename-outside&gt; &lt;min-temp&gt;</code><br>
+    <code>define &lt;name&gt; dewpoint fan &lt;devicename-regex&gt; &lt;devicename-outside&gt; &lt;min-temp&gt; [&lt;diff_temp&gt;]</code><br>
     <br>
     <ul>
       	May be used to turn an fan on or off if the outside air has less water.
 	<ul>
         <li>
-	Generate event "fan: on" if dewpoint of &lt;devicename-outside&gt; is lower
+	Generate event "fan: on" if (dewpoint of &lt;devicename-outside&gt;) + &lt;diff_temp&gt; is lower
 	than dewpoint of &lt;devicename&gt; and temperature of &lt;devicename-outside&gt; is &gt;= min-temp
-	and reading "fan" was not already "on". The event will be generated for &lt;devicename&gt;.</li>
+	and reading "fan" was not already "on". The event will be generated for &lt;devicename&gt;. Parameter &lt;diff-temp&gt; is optional</li>
 	<li>Generate event "fan: off": else and if reading "fan" was not already "off".</li>
 	</ul>
     </ul>