diff --git a/Sonoff-TH.md b/Sonoff-TH.md
index 4ec33535..db0a1093 100644
--- a/Sonoff-TH.md
+++ b/Sonoff-TH.md
@@ -6,6 +6,8 @@ TH10 has a relay rated to 10 amps and TH16 to 16 amps (Input voltage: 90~ 250V A
 
 The 2.5mm jack socket connects to GPIO14. 
 
+In PCB Ver 2.1 you can find a fifth pin next to the serial pins, labeled `EXP-LOG`. You can use this as GPIO2 to any generic purpose. Currently should make a custom template for it.
+
 ### Sonoff sensors with 2.5mm jack
 Sonoff sells 3 sensors with 2.5mm jack to use with the Sonoff TH.
  1. [Sonoff TH Sensor Si7021](https://www.itead.cc/wiki/Sonoff_Sensor_Si7021)