Summary of SECRET KNOCK UNLOCKS DOOR
This article describes an electronic door lock by IsmailSan that uses a secret knock to unlock. The system employs a piezoelectric speaker as a sensor to detect knock patterns, which are processed by an Arduino microcontroller. A servo motor actuates the deadbolt upon recognizing the correct sequence. The design is simple, requiring only an analog input circuit and a battery for portability.
Parts used in the Secret Knock Door Lock:
- Piezoelectric speaker
- Servo motor
- Arduino microcontroller
- Resistor
- Battery
- Analog input circuit components
Watch any movie about the years of prohibition, and you’ll probably see character gain admittance to a speakeasy by using a secret knock on the door. In the old movies, a little sliding door would open so the doorman could check you out and let you in. With [IsmailSan’s] electronic lock, the secret knock automatically unlocks the door. You can see a video of how it works, below.
(Ed Note: Grrr…GitHub repo got pulled between writing and publication. Go check out the in-links in the bottom paragraph if you’re interested in knock-detectors.)
The device uses a piezoelectric speaker to detect the knocking. A speaker is a transducer and like many transducers, it will work — to some extent — in either direction. A servo motor manages the deadbolt. An Arduino runs the whole thing.
The code is relatively simple. It holds an array of projected delays between knocks and compares what it hears to those delays. If you complete the sequence, the door unlocks. We probably would add some extra security if we were locking up the country’s gold supply, but for a light-duty lock, it should be fine.
The circuit is simple, too. There is an analog input tied to a resistor and the sensor. The Arduino is perfectly capable of driving a small servo directly. Add a battery and it is done.
It’s been a while since we’ve seen knock-operated locks around here, but they used to be all the rage. Here is a nice simple one, one that uses logic chips, and of course one built from 555s. If knocking isn’t your style, try replacing the piezo with a button or even a capacitive sensor. You can’t knock it!
Source: SECRET KNOCK UNLOCKS DOOR
-
How does the device detect the secret knock?
The device uses a piezoelectric speaker to detect the knocking. -
What component manages the deadbolt?
A servo motor manages the deadbolt. -
Can the door be unlocked with alternatives to knocking?
Yes, you can replace the piezo with a button or even a capacitive sensor. -
How does the code determine if the sequence is correct?
The code holds an array of projected delays between knocks and compares what it hears to those delays. -
Does the Arduino need external power drivers for the servo?
No, the Arduino is perfectly capable of driving a small servo directly. -
Is the circuit design considered complex?
No, the circuit is described as simple, involving an analog input tied to a resistor and the sensor. -
What was the historical context of knock-operated locks mentioned?
They used to be all the rage, with previous examples using logic chips or 555 timers.
