Here’s a superb DIY project which comes two outstanding hacks we’ve covered previously. It’s a steampunk mechanical iris combined with the secret knock detecting door to create this unique garage door opener.
The brassy mechanical iris hides the secret in an Arduino, a motor, and a piezo sensor. The three components work together to record and recognize a specific knocking pattern to unlock a door. The knocker basically detects the time gap between successive knocks and matches it with what’s fed into it. The secret knocking sequence can be re-programmed quite easily with the touch of a button. Awesome, I love it!