diff --git a/README.md b/README.md
index 9798801..48b466d 100644
--- a/README.md
+++ b/README.md
@@ -57,7 +57,8 @@ Arduino based project running on my custom made board
 
 ### I2C Hardware addresses :
 * OLED screen : 0x3C
-* RTC DS3231 : 0x68
+* RTC DS3231  : 0x68
+* PCF8574     : 0x27
 
 ### External librairies used :
 * Adafruit_SSD1306 (not my work) [link](https://github.com/adafruit/Adafruit_SSD1306)