diff --git a/src/main.cpp b/src/main.cpp
index d1241f3..ee4785e 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -104,9 +104,21 @@ struct sensordata
   // SW Serial
   //SW Serial RX: to mhz19 tx (green cable)
   //SW Serial TX: to mhz19 rx (blue cable)
-  //co2 sensor needs 5v
+  //co2 sensor needs 5v. Connect USB 5V directly (not through wemos d1 onboard diode which gives only 4.7V!)
 
   //if ABC is disabled (see in setup function) sensor should be calibrated manually. leave outdoors (=400ppm) with no direct sunlight for >20min, then connect HD pin to GND for at least 7 seconds.
+  /* Pinout  (view from top, connector at the bottom)
+  * Vin, GND, NC, PWM
+  *  |    |    |    |
+  * /-----------------\
+  * |                 |
+  * |                 |
+  * |                 |
+  * |                 |
+  * \-----------------/
+  *    |  |  |  |  |
+  *   Vo Rx Tx NC HD
+  */
 
   #include <SoftwareSerial.h>