How to make a secret knock activated drawer lock! Nothing says “There’s something valuable here!” than the sight of a lock. But what if the lock was invisible and the unlocking key could be transmitted through solid matter? No one would even know there was a lock, much less how to pick it.
That’s what the Secret Knock Activated Drawer Lock does. It hides all of the lock mechanism away and can only be unlocked by something you know: a secret pattern of knocks.
A solenoid locks secures the drawer while a piezo buzzer listens for knocks. A Trinket compares the knock pattern to the stored secret knock and if they match the solenoid latch retracts and the drawer can be opened. Setting your own custom knock is as simple as holding down a button and tapping the new rhythm.
The project is relatively straight forward and you should be able to complete it in an afternoon.
NEW PRODUCT – Lock-style Solenoid – 12VDC – Solenoids are basically electromagnets: they are made of a big coil of copper wire with an armature (a slug of metal) in the middle. When the coil is energized, the slug is pulled into the center of the coil. This makes the solenoid able to pull from one end.
This solenoid in particular is nice and strong, and has a slug with a slanted cut and a good mounting bracket. It’s basically an electronic lock, designed for a basic cabinet or safe or door. Normally the lock is active so you can’t open the door because the solenoid slug is in the way. It does not use any power in this state. When 9-12VDC is applied, the slug pulls in so it doesn’t stick out anymore and the door can be opened.
The solenoids come with the slanted slug as shown above, but you can open it with the two Phillips-head screws and turn it around so its rotated 90, 180 or 270 degrees so that it matches the door you want to use it with.
To drive a solenoid you will a power transistor and a diode, check this diagram for how to wire it to an Arduino or other microcontroller. You will need a fairly good power supply to drive a solenoid, as a lot of current will rush into the solenoid to charge up the electro-magnet, about 500mA, so don’t try to power it with a 9V battery!
