diff --git a/Keyboard_PS2/README.md b/Keyboard_PS2/README.md
index c5d1216..84cf7d6 100644
--- a/Keyboard_PS2/README.md
+++ b/Keyboard_PS2/README.md
@@ -4,6 +4,8 @@
 
 Needs Atmega32u4 (e.g. Arduino Leonardo).
 
+PS/2 is 5V.
+
 Needs custom ps2-library (PS2Keyboard_mcgurk.zip, unzip to libraries-folder).
 
 Clock-signal must be in pin 2 (because of interrupts).