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Automatic Secret Knock-Detecting Door Opener
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A few secret knock detecting Arduino projects exist around the web, meaning the basic micro-controller logic for the knock sensing function has been fleshed out. With confidence that the software end would work, I set out to build a secret knock detecting door opener that would open my door if provided a secret knock.
Idea
My original plan was to interface with the electric deadbolt in my apartment door, but upon inspection the unit is upwards of $900... and I'd prefer not to take any chances messing with the internals. A bit less elegant is a mechanical system that would open the door by the door handle itself. Since the project requires no finesse or accuracy in motor control, I figured a cheap high torque servo motor flipped through a pulley would likely do the trick. An MG995 13Kg-cm high torque servo costs about $6-7 and can be modified for full rotation. I designed a custom winch system to pull the door knob open.
Basic Circuit
Because the Arduino handles all the analysis and control, the circuit is relatively simple. I've sketched it out on the right. A variable potentiometer allows the sensitivity to be adjusted and the LEDs indicate success or failure of the knock for debugging purposes.
Prototyping the Arduino Shield
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Finalizing and Rebuilding a Reliable Shield
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Designing a Winch System
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Parts Used:
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