diff --git a/samp_spd b/samp_spd
index 77074722c44c8865245a6f4d642a105c4c96ad2d..fc270a8f952336aedab75647def1fe2219d7deb4 100644
--- a/samp_spd
+++ b/samp_spd
@@ -1,6 +1,7 @@
 // Reference: https://forums.raspberrypi.com/viewtopic.php?t=368639
+//https://www.hackster.io/AlexWulff/adc-sampling-and-fft-on-raspberry-pi-pico-f883dd
 
-#include <Arduino.h>
+#include <Arduino.h> //https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/cores/arduino/main.cpp
 
 int led =25;
 UART pc1(4, 5, NC, NC);