diff --git a/Code/devterm_fan_daemon_cm4/README.md b/Code/devterm_fan_daemon_cm4/README.md
index d6d18cd..ba6c746 100644
--- a/Code/devterm_fan_daemon_cm4/README.md
+++ b/Code/devterm_fan_daemon_cm4/README.md
@@ -23,4 +23,15 @@ then restart systemd service to take effect
 
 `sudo systemctl restart devterm-fan-temp-daemon`
 
+## How to control the fan from GPIO
+
+``` start the fan
+sudo gpio mode 17 out
+sudo gpio write 17 1
+```
+
+```stop the fan
+sudo gpio mode 17 out
+sudo gpio write 17 0
+```