Design Constraints Bring Lockbox To Life

April 27, 2025 by Bryan Cockfield 1 Comment

One of the most paradoxical aspects of creating art is the fact that constraints, whether arbitrary or real, and whether in space, time, materials, or rules, often cause creativity to flourish rather than to wither. Picasso’s blue period, Gadsby by Ernest Vincent Wright, Tetris, and even the Volkswagen Beetle are all famous examples of constraint-driven artistic brilliance. Similarly, in the world of electronics we can always reach for a microcontroller but this project from [Peter] has the constraint of only using passive components, and it is all the better for it.

The project is a lockbox, a small container that reveals a small keypad and the associated locking circuitry when opened. When the correct combination of push buttons is pressed, the box unlocks the hidden drawer. This works by setting a series of hidden switches in a certain way to program the combination. These switches are connected through various diodes to a series of relays, so that each correct press of a button activates the next relay. When the final correct button is pushed, power is applied to a solenoid which unlocks the drawer. An incorrect button push will disable a relay providing power to the rest of the relays, resetting the system back to the start.

The project uses a lot of clever tricks to do all of this without using a single microcontroller, including using capacitors that carefully provide timing to the relays to make them behave properly rather than all energizing at the same time. The woodworking is also notable as well, with the circuit components highlighted when the lid is opened (but importantly, hiding the combination switches). Using relays for logic is not a novel concept, though; they can be used for all kinds of complex tasks including replacing transistors in single-board computers.

Continue reading “Design Constraints Bring Lockbox To Life” →

Custom Pneumatic Cylinders Lock This Monitor Arm In Place

August 9, 2024 by Dan Maloney 8 Comments

Few consumer-grade PCs are what you’d categorize as built to last. Most office-grade machines are as likely as not to give up the ghost after ingesting a few too many dust bunnies, and the average laptop can barely handle a few drops of latte and some muffin crumbs before croaking. Sticking a machine like that in the shop, especially a metal shop, is pretty much a death sentence.

And yet, computers are so useful in the shop that [Lucas] from “Cranktown City” built this neat industrial-strength monitor arm. His design will look familiar to anyone with a swing-arm mic or desk light, although his home-brew parallelogram arm is far sturdier thanks to the weight of the monitor and sheet-metal enclosure it supports. All that weight exceeded the ability of the springs [Lucas] had on hand, which led to the most interesting aspect of the build — a pair of pneumatic locks. These were turned from a scrap of aluminum rod and an old flange-head bolt; when air pressure is applied, the bolt is drawn into the cylinder, which locks the arm in place. To make it easy to unlock the arm, a pneumatic solenoid releases the pressure on the system at the touch of a button. The video below has a full explanation and demonstration.

While we love the idea, there are a few potential problems with the design. The first is that this isn’t a fail-safe design, since pressure is needed to keep the arm locked. That means if the air pressure drops the arm could unlock, letting gravity do a number on your nice monitor. Second is the more serious problem [Lucas] alluded to when he mentioned not wanting to be in the line of fire of those locks should something fail and the piston comes flying out under pressure. That could be fixed with a slight design change to retain the piston in the event of a catastrophic failure.

Problems aside, this was a great build, and we always love [Lucas]’ seat-of-the-pants engineering and his obvious gift for fabrication, of which his wall-mount plasma cutter is a perfect example.

Continue reading “Custom Pneumatic Cylinders Lock This Monitor Arm In Place” →

This Robot Picks Locks, If You’re Very Patient

May 5, 2024 by Dan Maloney 17 Comments

We all know the Hollywood trope of picking a lock with a paperclip, and while it certainly is doable, most reputable locks require slightly more sophisticated tools to pick effectively. That’s not to say that wire is off the table for locksports, though, as this cool lock-picking robot demonstrates.

The basics behind [Sparks and Code]’s design are pretty simple. Locks are picked by pushing pins up inside the cylinder until they line up with the shear plane, allowing the cylinder to turn. Normally this is done a pin at a time with a specialized tool and with a slight bit of torque on the cylinder. Here, tough, thin, stiff wires passing through tiny holes in a blade shaped to fit the keyway are used to push all the pins up at once, eliminating the need to keep tension on the cylinder to hold pins in place.

Sounds simple, but in practice, this looks like it was a nightmare. Getting five wires to fit into the keyway and guiding them to each pin wasn’t easy, nor was powering the linear actuators that slide the wires in and out. Applying torque to the lock was a chore too; even though tension isn’t needed to retain picked pins, the cylinder still needs to rotate, which means moving the whole picking assembly. But the biggest problem by far seems to be the fragility of the blade that goes into the keyway. SLA might not be the best choice here; perhaps the blade could be made from two thin pieces of aluminum with channels milled on their faces and then assembled face-to-face.

The robot works, albeit very slowly. This isn’t [Sparks and Code]’s first foray into robot lock picking. His previous version attempted to mimic how a human would pick a lock, so this is really thinking outside the box.

Continue reading “This Robot Picks Locks, If You’re Very Patient” →

Flashlight Door Lock Is A Bright Idea

December 29, 2023 by Kristina Panos 45 Comments

There are many ways to lock a door. You could use a keypad, an RFID card, a fingerprint or retina scan, Wi-Fi, Bluetooth, the list goes on. You could even use a regular old metal key. But none of these may be as secure as [mircemk]’s Arduino-based door lock that employs a smartphone’s flashlight as a pass code.

At first blush, this seems horribly insecure. Use a plain old flashlight to open a door? Come on. But the key is in the software. In fact, between the typed-in pass code and the flash of light it generates, this lock kind of has two layers of security.

Here’s what’s going on: inside the accompanying smart phone application, there’s a list of passwords. Each of these passwords corresponds to a flash of light in milliseconds. Enter the correct password to satisfy the Arduino, and the phone’s flashlight is activated for the appropriate number of milliseconds to unlock the door.

As you’ll see in the video below, simply flashing the light manually doesn’t unlock the door, and neither does entering one of the other, bogus passwords. Although it does activate the flashlight each time, they don’t have the appropriate light-time length defined.

Hardware-wise, there is an Arduino Nano Every in charge of the LDR module that reads the flashlight input and the 12 V relay that unlocks the door. Be sure to check it out it the video after the break.

If you want to keep your critters from bringing wild critters back inside, check out this Wi-Fi cat door that lets you have a look at what might be dangling from their jaws before unlocking the door.

Continue reading “Flashlight Door Lock Is A Bright Idea” →

Presence Sensor Locks Computer When You Step Away

July 2, 2023 by Bryan Cockfield 14 Comments

Having a computer that locks its screen after a few minutes of inactivity is always a good idea from a security standpoint, especially in offices where there is a lot of foot traffic. Even the five- or ten-minute activity timers that are set on most workstations aren’t really perfect solutions. While ideally in these situations we’d all be locking our screens manually when we get up, that doesn’t always happen. The only way to guarantee that this problem is solved is to use something like this automatic workstation locker.

The project is based around the LD2410 presence sensor — a small 24 GHz radar module featuring onboard signal processing which simplifies the detection of objects and motion. [Enzo] paired one of these modules with a Seeed Studio XIAO nRF52840 development board to listen to the radar module and send the screen lock keyboard shortcut to the computer when it detects that the user has walked away from the machine. The only thing that [Enzo] wants to add is a blinking LED to let the user know when the device is about to timeout so that it doesn’t accidentally lock the machine when not needed.

One of the parts of this build that is a little bit glossed over is the fact that plenty of microcontroller platforms can send keystrokes to a computer even if they’re not themselves a USB keyboard. Even the Arduino Uno can do this, so by now this feature is fairly platform-agnostic. Still, you can use this to your advantage if you have the opposite problem from [Enzo] and need your computer to stay logged in no matter what.

Simple Wi-Fi Cat Door Solves The Extra Critter Problem, And Nothing More

November 2, 2022 by Dan Maloney 11 Comments

Anyone with an outdoor cat in their life knows their propensity for bringing home offerings, in the form of critters in various stages of the process of becoming ex-critters. And anyone with a hacker in their life knows that there’s a tendency to throw technology at this problem. But sometimes, the simplest solutions are the best.

Take this simple stepper-powered cat door lock. For [Jason Winfield], the essential problem with his outdoor cat’s late-night demands for reentry was having to manually unlock the cat door after a quick visual check that no midnight snacks were along for the ride. Such activity tends to make it hard to get back to sleep. One natural reaction to this would be to completely automate the process with machine learning to recognize the offering and deny entry; we’ve seen exactly that before, after all. But recognizing that the disruptive part was the getting up to check bit, [Jason] just whipped up a simple stepper-driven lock with an ESP8266 microcontroller. With a 3D-printed case and a battery pack, and a nearby Wi-Fi camera, the lock denies entry to the cat until he gets a look at it, at which point he simply hits the lock’s webpage to unlock the door. The video below would show the lock in action, except the cat buggered off once it got a whiff of the doings. Cat’s gonna cat.

What we appreciate about this project is its simplicity. It solves the problem with the minimum feature set, which is something we see too little of sometimes. It’s also got some nice ideas, like the non-captive bolt that can be removed to unlock the door if the battery dies. Smart thinking, [Jason], and sweet dreams.

Continue reading “Simple Wi-Fi Cat Door Solves The Extra Critter Problem, And Nothing More” →

Making A “Unpickable” Lock

November 29, 2020 by Danie Conradie 51 Comments

Every time manufacturers bring a new “unpickable” lock to market, amateur and professional locksmiths descend on the new product to prove them wrong. [Shane] from [Stuff Made Here] decided to try his hand at designing and building an unpickable lock, and found that particular rabbit hole to be a lot deeper than expected. (Video, embedded below.)

Most common pin tumbler locks can be picked thanks to slightly loose fits of the pins and tiny manufacturing defects. By lifting or bumping the pins while putting tension on the cylinder the pins can be made to bind one by one at the shear line. Once all the pins are bound in the correct position, it can be unlocked.

[Shane]’s design aimed to prevent the pins from being set in unlocked position one by one, by locking the all pins in whatever position they are set and preventing further manipulation when the cylinder is turned to test the combination. In theory this should prevent the person doing the picking from knowing if any of the pins were in the correct position, forcing them to take the difficult and time-consuming approach of simply trying different combinations.

[Shane] is no stranger to challenging projects, and this one was no different. Many of the parts had to be remade multiple times, even with his well-equipped home machine shop. The mechanism that holds the pins in the set position when the cylinder is rotated was especially difficult to get working reliably. He explicitly states that this lock is purely an educational exercise, and not commercially viable due to its mechanical complexity and difficult machining.

A local locksmith was unsuccessful in picking the lock with the standard techniques, but the real test is still to come. The name [LockPickingLawyer] has probably already come to mind for many readers. [Shane] has been in contact with him and will send him a lock to test after a few more refinements, and we look forward to seeing the results! Continue reading “Making A “Unpickable” Lock” →