Hacked Gadgets Forum

June 12, 2007

Knock to Open Door

at 1:22 pm. Filed under Complex Hacks, Electronic Hacks, Funny Hacks

Sprite Mods sent in a fantastic Knock to Open Door hack that they have just come up with. It is a door that will unlock when the correct knock pattern is performed. Funny thing is I had a similar idea a few years ago except my idea was to use the door bell as an input device and use bi-color LEDs mounted inside the door bell as indicators to allow the user to enter in a code.

Video after the jump.

“After some brainstorming, we came up with a James Bond-worthy concept: knock on the door in a certain fashion, and the door’ll open automatically. The idea was perfect: no need to drill holes, sneaky enough so the landlord wouldn’t accidentally trigger it, easy enough to remember.

The complete device gets its power from a laptop PSU. The power-supply is riddled with capacitors: we’re switching coils here, so there will be lots of EMF introduced on the power-supply-lines and we don’t want that messing with our CPU. In the middle, the brains of the thing: an ATTiny2313. The ATTiny drives four BUZ11 MOSFETs, who in turn switch the bipolar stepper motor which turns the knob. While not drawn, the BUZ11s have integrated ESD-protection diodes to protect form EMF backlash by the motors coils.

To convince the device to turn its motor, two ways are provided: first of all, a set of buttons for testing purposes. Secondly, there’s the analogue stuff right from the microcontroller, which basically is an elektret microphone plus a really crude and hacked pre-amp. It took some fiddling to get the resistor values right, but when I drew the schematic of what I had built, that turned out to be no surprise: as you can see in the schematic, T2 is upside-down, with its collector and emitter switched. ”



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17 Responses to “Knock to Open Door”

  1. joebob Says:

    I might add this to my list of locks to get through for a big safe…..

  2. ryan Says:

    cool i likey, just hope nobody whos watching has a tape recorder………

  3. Mitten Says:

    If i ever own a bank, this will be the first door to the vault

  4. Haseeb A Says:

    what will be the second??

    not bad!!

  5. Mr. Maigo Says:

    Great hack

  6. MAKE: Blog Says:

    Knock to open

    Sprites mods writes -What to do if you are renting a room in students flat and want to make use of an unused, empty room? You just walk in and do your thing. What if the landlord, for some…

  7. Il Liceo » Blog Archive » Knock to open Says:

    […] Sprites mods – Knock to open – Intro – [via] Link. […]

  8. Ed T. Says:

    Great hack, and I’m all for DIY, but in case you don’t have the skillz or need it NOW, there’s this.

  9. Ed T. Says:

    Whoops, no HTML? Here’s the link:

  10. Alan Parekh Says:

    Hi Ed T,

    Great find, who would ever think there would be knock to open system available for purchase! It seems to be harder and harder to create anything that is unique anymore…

  11. Knock to open » Developages - Development and Technology Blog Says:

    […] Sprites mods – Knock to open – Intro – [via] Link. […]

  12. Ed T. Says:


    Well, as Barbara Grizzuti Harrison once said, “There are no original ideas, only original people”. 🙂 Besides, as an engineer the challenge is always not to invent a brand new thing, but to execute an existing idea in as an efficient manner as possible or to retask an existing idea for a new purpose.

    BTW, love the blog – one of the few that stay in my RSS stream.

  13. graywave Says:

    I hope it can handle more complicated knocks than that. Similar to passwords; longer is better.

  14. Il Liceo | Knock to open Says:

    […] Sprites mods – Knock to open – Intro – [via] Link. […]

  15. Haseeb Anjum Says:

    well said Ed. T

  16. Silver Says:

    This is really cool… A secret knock

  17. Doni Says:

    Hi mate i am from UK and i need help. I have lost all the keys from the back door.So the only way we can open the flat is by calling to our flat using Intercom which is on the back door and hoping that someone is at home to open the door for us. So i was wondering if it’s possible to hack someway my Intercom which is inside my flat so when people would call from Back Door’s Intercom to my flat it would open door for them automatically.

    I know it’s possible some way because my friend’s house have the same system,people have to press just one secret button ”Trade” at the back door,and the door is open. But if you go inside his flat and take the handset from his intercom you can here the noise from the street even if you hang up it ,so it’s 24hours ON

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