Knock response automatic door opener

I’m at the beach this week – finally on vacation. Thanks to DD-WRT, I’ve got a handy wireless repeater to keep the beach house covered with network access. [sprite_tm]’s doing his best to make my vacation easier. He built this knock activated automatic door opener for a friend who wanted easy access to some locked, but empty flat (think british apartment) rooms. He used an ATTINY with some fets to drive the stepper (you can find those in old dot matrix printers for free) and a small transistor amped mic circuit to pick up the knocks. Knock the right code, and you’ll get let right in.

17 thoughts on “Knock response automatic door opener

  1. I remember seeing a similar commercial product. Everything was mounted within a door so it could not be tampered with. the “knock code” was so long and precise it used a small battery powered key to do the knocking.

  2. Well, it looks unsafe, but it’s like the apartment entrydoor opener connected to your doorbell, if you won’t know it’s there, no one will brute-force knock you!
    and because it’s a empty building, your neighbors won’t get tired from your knock-sequence, so they won’t give it a try someday..
    nice hack!

  3. Another interesting idea for this would be using a few hall-effect detectors set in several spots on the inside of the door. To open the door you just put a small neodym magnet close to where you know the detectors are, then the door pops open.

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