diff --git a/README.md b/README.md
index 0ff1c75..fcf349a 100644
--- a/README.md
+++ b/README.md
@@ -32,6 +32,43 @@ looking down, Pin1 is top left, Pin40 bottom right
 
 ```
 
+Note that the spare onboard LED (activity?) is on `PD18`
+
+## LoRA HAT pins
+This is derived from the schematics; showing the 5 specific pins used (only)
+
+```text
+looking down, Pin1 is top left, Pin40 bottom right
+
+        3v3  -- o o -- 5v
+                o o -- 5v
+                o o -- GND
+    AUX  ------ o o ------ TX (set to USB serial via jumpers on HAT)
+         GND -- o o ------ RX (set to USB serial via jumpers on HAT)
+             -- o o --
+    M1   ------ o o -- GND
+    M0   ------ o o --
+         3v3 -- o o --
+             -- o o -- GND
+             -- o o --
+             -- o o --
+         GND -- o o --
+             -- o o --
+             -- o o -- GND
+             -- o o --
+             -- o o -- GND
+             -- o o --
+             -- o o --
+         GND -- o o --
+
+```
+The three fixed pins used by the HAT are 7,13 and 15.
+These map as follows:
+* `AUX` is on `PB7`
+* `M1` is on `PD22`
+* `M0` is on `PB0`
+
+The Serial (TX,RX) is deselected via onboard jumpers, a secondary serial will be jumpered to the module TX/RX instead.
 
 ## References
 #### MQ Pro