diff --git a/Software/Pinout.md b/Software/Pinout.md
index 9269b86..f5514d5 100644
--- a/Software/Pinout.md
+++ b/Software/Pinout.md
@@ -35,3 +35,4 @@
 |Beeper| Pin 5 (PWM)
 |Stop Button|Reset
 |Temp CS, MISO, SCLK|6, 7, 8 (Soft-SPI)
+|Optokoppler|9 (active high)