added documentation

Sonoff-SV.md

@@ -1,3 +1,54 @@
 # Sonoff SV Version 1.0 (Work in Progress)
 
+* Itead Product Page: 
+* Itead Shop: https://www.itead.cc/sonoff-sv.html
+* Itead Wiki: https://www.itead.cc/wiki/Sonoff_SV
+
+The sonoff safe voltage is almost the same as the sonoff basic.
+It has the ESP 8266 with 1MB flash
+
+## difference between sonoff basic
+* It can be powered by DC voltage
+* It has extra GPIO pin headers
+* It has two LED status lights (RED and GREEN)
+* The traces on the bottom aren't soldered
+* The GND,TX,RX and 3v3 pins are labeled 
+
+| Usable GPIO pins  |
+| ------------- |
+| GPIO4 |
+| GPIO5  | 
+| GPIO14  | 
+
+### ⚠️ what can the unit handle ⚠️
+The trace is 2 mm wide.
+By assuming the pcb trace thickens is 1 oz/ft^2
+
+with that information you can calculate the current:
+2 A
+
+If you are using more current be sure to put solder on the solder pad area.
+
+# using the sonoff SV
+You can use the sonoff SV in three different ways.
+
+### 1. with variable DC voltage between 5-24 V 
+By not having the jumper connected in the far left. the voltage regulator is used for the relay.
+
+### 2. with solid DC voltage 5 V
+By bridging the two pins you are connecting the 5 V input directly to the relay so you are bypassing the regulator so the relay still gets 5 V
+
+### 3. ⚠️ with AC voltage ⚠️ 
+
+⚠️ ⚡️ WARNING ONLY DO THIS WHEN YOU KNOW WHAT YOU ARE DOING. ⚡️ ⚠️ 
+
+By removing the two 0 ohm SMD resistors next to the jumper you are disconnecting the voltage input from the logic.
+By doing this you can switch AC again like the sonoff basic.
+Than You can use the jumpers labeled 5~12 V as your DC voltage for the ESP and relay. 
+
+
+***
+
+![](https://www.itead.cc/wiki/images/4/47/Sonoff_SV_mode.jpg)
+
 ![](https://i.imgur.com/ps8t37j.jpg)