Secret Knock Activated Drawer Lock

Make sure everything works before installing it.

Unplug the Trinket from USB and plug in the 12V power supply and then be sure it can accurately detect a knock, unlock on command, and record new knocks, as described below.

If it doesn't behave, see the "Troubleshooting" section for what might be going wrong.

Startup:

The Trinket's green power LED will light up.
The Trinket's red LED will light up.
The solenoid lock will click open twice. (First really quickly, the second time for about a second or two.)
The Trinket's red LED will turn off and the lock will close.

When the red light goes out and the lock closes, it's now listening for a knock and is ready to go.

Operation:
The default secret knock is the classic Shave And A Haircut. To change it, see "recording" below.

The red LED will blink when it senses a knock. (It should also sense if you lightly tap the piezo with your finger.)
If the wrong sequence if knocks (or taps) is detected the red LED will flicker briefly.
If the correct sequence is detected the red LED will light and the lock solenoid will retract for a couple seconds.

Recording a new secret knock:

Press the record button. The red LED will light and the piezo will play a short tone to let you know its listening for a new knock. (Note: This button won't work if it senses a knock in the last couple of seconds.)
(If you change your mind, press the button again and the red light will go off, and it will play a different tone.)
Kock your new knock pattern. The red light will blink off when it hears a knock.
When you're done, wait a second or two for it to register. It will then playback the knock pattern by both blinking the red LED and beeping the piezo.
This is now saved as a new knock and it will be remembered even if it's powered off.
If you don't like the knock or you made a mistake, press the button again to record a different pattern.

Now that you're sure that it works, it's time to install it.