diff --git a/README.md b/README.md
index 3d1718d..c754ba3 100644
--- a/README.md
+++ b/README.md
@@ -109,7 +109,9 @@ You can also use Arduino vice versa. You cannot read USB with normal Arduino, bu
 https://github.com/felis/USB_Host_Shield_2.0
 
 ### Software USB
-USB-device without ATmega16u2/32u4: https://www.obdev.at/products/vusb/index.html
+USB-device without ATmega16u2/32u4. Needs 3 resistors and 2 zender diodes.
+
+https://www.obdev.at/products/vusb/index.html
 
 ### Other ideas
 Of course Arduino can be used many other ways. Add a PIR motion detector module from Ebay (under $2) and your computer wakes up from sleep when you walk to room. Just read PIR-sensor data pin and if it is 1, send some keyboard button (which normally does nothing) to computer so it wakes up. Or make info-board to your kitchen or hallway wall from old Android tablet and it turns on backlight only when someone goes to kitchen.