Summary of Knock To Open Treasure Chest
The author built a rechargeable, keypad-free treasure chest for their daughter using a "Secret Knock" activation system. The device features a programmable knock sequence to unlock via a piezo sensor and a servo motor for the latch. It runs on a Li-ion battery charged through a PowerBoost module, eliminating external power cables while ensuring the box remains functional when closed.
Parts used in the Knock To Open Treasure Chest:
- Arduino Nano V3.0
- PowerBoost 1000 Charger
- Li-ion battery 1000mAh 3.7V
- SG90 micro servo motor | 5V | 9g
- Piezo buzzer
- Piezo sensor trigger drum disc
- Switches, resistors and LEDs
- Screws and glue
Preface
My daughter asked me to build her a treasure chest that she could use to store her most valuable things. Obviously she demanded it to have some kind of a locking mechanism so only she could open the box.
First thought was to use a keypad but then her grandfather bought her a diary with a secret code. So I had to come up with something else. On Adafruit’s tutorials I came across the Secret Knock Activated Drawer Lock. Use a secret combination of knocks to open the box. An idea I instantly liked a lot. Another great thing about this drawer lock was that it was programmable, which means you can change the knock sequence to anything you like.
Thoughts
I still had to think about the closing mechanism and decided to use a servo motor. Also I wanted the box to run without power cables. But if I used batteries I would run into a problem with the box closed and the batteries without power. So it had to be rechargeable but also I had to think of how to charge them from the outside of the box. Browsing on Adafruit’s page I came across the PowerBoost 1000 Charger, a neat thing to power any Arduino like microprocessor while also charging a Li-ion battery.
I also thought about making the box somehow connected either via Bluetooth or WiFi so I could operate the closing mechanism via a smartphone. But in the end I decided against it for the sake of simplicity, at least for version 1.
Bill of material
- Arduino Nano V3.0
- PowerBoost 1000 Charger
- Li-ion battery 1000mAh 3.7V
- SG90 micro servo motor | 5V | 9g
- Piezo buzzer
- Piezo sensor trigger drum disc
- Switches, resistors and LEDs
- Screws and glue
Woodworking
I wanted to build a nice box with finger joints. But I soon had to discover that was not an easy task to do with a circular saw. I followed this tutorial (German only).
Read More: Knock To Open Treasure Chest
- Why was a keypad not used for the lock?
The author chose a secret knock mechanism instead because the daughter received a diary with a secret code, prompting a desire for a different unlocking method. - How is the box powered without external cables?
The project uses a rechargeable Li-ion battery paired with a PowerBoost 1000 Charger to allow operation without power cables. - What component handles the closing mechanism?
A SG90 micro servo motor was selected to operate the closing mechanism of the treasure chest. - Can the opening sequence be changed?
Yes, the drawer lock is programmable, allowing users to change the knock sequence to anything they like. - Why was Bluetooth or WiFi connectivity rejected?
Connectivity options were decided against for version 1 to maintain simplicity. - What type of joints were originally planned for the woodwork?
The author initially wanted to build the box with finger joints but found them difficult to execute with a circular saw.
