Magnetic Security Lock
Objectives
In the fall semester of 2021, I was enrolled in ENGR 1050: Product Realization, a Capstone design course that works with industry partners to facilitate product development. Our team consisted of four engineering students spanning multiple disciplines and our sponsor Marc Tobias, an engineer and lawyer based in Pittsburgh. Marc has decades of experience - he’s written for Forbes, testified as an expert security witness in numerous trials, and penned several books. At the time, he was working with a company called Magnasphere that manufactures magnetic switches.
Marc tasked us with using these switches to reimagine the electromagnetic lock and key. Could we pulse these switches, thereby generating a “magnetic code” (think morse code) that would act as the grooves on a typical mechanical key? Could we develop a lock that reads this code and evaluates whether it is a perfect fit, then unlock a door?
If this was possible, we would need to construct a proof of concept for both the transmitter (key) and receiver (lock). If not, we would need to provide ample evidence to support that claim based on the specifications of the Magnasphere switches.
How does it work?
2.
The ball inside of the housing moves across it, making contact with the electrode
In this video, a solenoid is pulsing a magnetic field in front of the Magnasphere switch.
Listen for the clicks of the magnetic ball striking the electrode.
3.
The circuit is complete and the switch is closed when the electrode touches the magnetized ball
The Magnasphere
The Magnasphere is not your ordinary magnetic switch. Here’s why:
It’s far more cost-effective than a typical Hall Effect or Reed switch
It’s made of durable materials that aren’t susceptible to brute force
It does not malfunction when exposed to “defeat magnets” or excessively large magnetic fields.
1.
An external magnet is brought close to the Magnasphere.
The Prototype
Our final proof of concept involved two microcontrollers, a switch, the Magnasphere, a magnet (coil), and an LED. We were able to pulse a code in the form of a square wave from one microcontroller at a maximum of 20 Hz. There are 8 bits of the code that the other microcontroller decodes and if deemed correct, will turn on an LED. If incorrect, no signal will be sent to the LED. In practice, the LED would be substituted by an actuator that would unlock the door.
This is an example 8-bit code, as seen on an oscilloscope. The binary for this code is 01000110, which equates to the number 70. There is noise present due to the magnet settling down.
The Design Expo and Beyond
At the end of the semester, we presented our prototype at the Swanson School of Engineering Design Exposition to several in-person and virtual judges. We were awarded second place among the Product Realization teams and received a B+ in the course. Tobias even mentioned that he was working on a patent for our technology. However, future groups still needed to build upon our work in following semesters of the course. We outlined several design goals to help the next team pick up where we left off:
Downsize and refine the circuits from a breadboard to a printed circuit board.
Incorporate a “slot” in the receiver to press the transmitter into based on the precise distance between the Magnasphere and coil required for the Magnasphere to switch on and off.
Add a secondary Magnasphere, one that is normally open instead of normally closed for added security and encryption.
Because Marc Tobias owns the intellectual property rights, our team was not able to be involved for the continued duration its development. At the end of the spring semester of 2023, I attended the Design Expo to see what the latest team had come up with. They showed a fully functioning lock and key with 3D printed housing and increased complexity of the magnetic code. I’m looking forward to seeing how the next group advances this project at this year’s Design Expo!
The team (from left to right): Markos Petkopoulos, Lauren Harrington, Jackson Walti, and Jake Brooks