diff --git a/README.md b/README.md
index 1361873..1cc4313 100644
--- a/README.md
+++ b/README.md
@@ -124,7 +124,7 @@ sudo openocd -f interface/ftdi/digilent-hs1.cfg -f interface/ftdi/swd-resistor-h
 Pins
 ----
 
-The [pinout guide for the Node151](http://resource.heltec.cn/download/LoRa_Node_151/LoRa_Node_151_Pinout_Diagram.pdf).
+The [pinout guide for the Node151](https://resource.heltec.cn/download/LoRa_Node_151/LoRa_Node_151_Pinout_Diagram.pdf).
 
 The default pins PB5-7,9 are used as active low controls for the relays.
 They are mapped to channels 0 through 3 respectively.  The LED on PB8