Pepper Mill Locks Your Door

Pepper! If you’ve ever tried to grind it, you’ve probably noticed it takes a bit of elbow grease. It’s actually possible to source electric pepper mills to grind it for you, in fact. It just so happens that [MarioM66] had one to hand, and a door lock that needed automating.

Seeing as grinding pepper requires at least as much torque as turning an average key in an average lock, the electric pepper mill makes perfect sense to use as a lock actuator. This build actually uses the electric pepper mill to directly turn the key in the lock, courtesy of an adapter to couple the square output shaft to the key. The adapter was crafted out of a moldable plastic called MultiMorph. The pepper mill is being used for its high-torque motor & gearbox, which makes it absolutely perfect for this application.

The rest of the project leans heavily on the hacker’s go-to, an Arduino and some off-the-shelf gesture recognition modules. Now, it’s possible to lock and unlock the door at the press of a button or the wave of a hand! Video after the break.

It’s great to see run-of-the-mill objects hacked into useful parts for new projects. In the same vein, check out this car that lets you fistbump to unlock.

17 thoughts on “Pepper Mill Locks Your Door

    1. It has advantages. You could tell someone how to get in without having to give them a key. A gesture would probably be easier to remember than a combination. Easier to guess, too, but I don’t think people would intuitively expect a gesture to work.

      Most of all, no more losing your house key. I keep mine in my wallet and pretty much never have any problems, but I know some people who just can’t help themselves.

  1. how long will the motor or its commutators last rotating in the reverse direction?
    what should I look for to determine if a motor will last while rotating in the other direction?

    1. That’s the beauty of it. Locking and unlocking are just turns in the opposite direction. Each time reverses the wear done by the last! This thing’s gonna last for-ev-er!

    2. I was not sure how to word concerns so I looked it up, its point umber 5 in the Practical Conclusions section at


      “Running the motor in the forward direction is likely to make it last longer. This is because the brushes are now being ‘dragged’ over the commutator rather than ‘pushed’ over the commutator. This in turn tends to reduce brush vibration, which then reduces the amount of arcing that can take place between the brush and commutator surfaces. Since arcing causes the brush and commutator surfaces to erode and oxidise, less arcing means better quality motor commutation for longer.”

  2. With the key permanently in the lock, the pins are disengaged, leaving the lock “unlocked”. I guess you’d still have to fight this pepper grinder to turn the cylinder from the outside, but still.

    I do like the idea of an electric pepper mill as a ready made high torque servo.

    1. That’s a very good point. You could always seal up the other side of the door, removing the keyhole or knob–but that means you are SOL if the automatic mechanism fails.

  3. Maybe mkII could swap in an airsoft motor/gearbox assembly for a lower profile.
    How long until someone knocks the pepper mill & shears the key off in the lock. Alternatively buy (gasp) one of the many commercial electronic locks and splice in the gesture circuit.

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