This is a simple application that stores the timing of button presses (within a 5 second period), then replays the sequence back out by flashing an LED in the same timing intervals. This was based on a secret knock program I did a long time ago.

Revision:
0:11f1739fb2ad
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os.lib	Tue Jun 27 20:40:36 2017 +0000
@@ -0,0 +1,1 @@
+https://github.com/armmbed/mbed-os/#c9e63f14085f5751ff5ead79a7c0382d50a813a2