The request that kicked things off
One of our long-time mechanical design partners reached out with a client who had an idea for a new kind of personal access badge. The concept was simple on the surface: build a small, battery-powered badge holder that could carry a photo ID and provide an electronic signal about whether a user had permission to access a restricted space.
Instead of putting the smarts in the badge itself, the design relied on a companion phone app 📱. The badge would contain only a low-power BLE radio and a few LEDs. The phone app would use geofencing to detect when the user approached an entry point, confirm permissions against the backend system, and then send a command to the badge to display status: green LED for access allowed, red LED for denied.
Our job at Embedded Engineering Solutions (EES) was to implement the embedded side of the system. On paper, it was straightforward: receive a command and drive the right LED. But like most projects, things evolved over time.
A project in three stages
Stage 1: The minimal viable badge
The first request was as simple as they come—implement basic commands so the phone app could tell the badge to turn on the red or green LED. We also added a battery monitor 🔋 to report low power status back to the app. That initial firmware came together quickly, with only a few hours of work.
Stage 2: Device pairing and updates
As soon as the first prototypes were in use, the client realized they needed a way to ensure each phone was paired with its correct badge. Without that, any phone could talk to any badge within range.
We designed a lightweight password-based system so that each badge could be securely linked to a single phone. At the same time, we added over-the-air firmware update support so the system could evolve in the field without physical access to the hardware.
Stage 3: Rethinking the power source
The original design ran on a replaceable CR2032 coin cell. That kept the hardware compact and simple, but the client soon asked about a rechargeable option. We explained the trade-offs: a rechargeable LiPo would need more frequent charging because of lower energy density, but it would eliminate the ongoing cost and hassle of replacing coin cells.
The client opted for the rechargeable path. We revised the hardware to support LiPo charging, added protection circuitry, and updated the end-of-line test process. This was a good example of our hardware design services, where we help clients navigate practical trade-offs between cost, usability, and long-term maintenance.
Beyond prototypes: supporting production
Our work didn’t stop at prototypes. We developed a simple self-test routine for end-of-line manufacturing 🏭 and worked with the client’s chosen contract manufacturer to transition the design into full production. That kind of prototyping-to-production support is where we often add the most value—bridging the gap between engineering samples and a design that can be built consistently on a factory line.
Since that launch—more than seven years ago—the badge has remained in production. Apart from a few minor component substitutions for obsolescence, the design has stood the test of time.
What we learned
Even small embedded projects tend to grow in scope as real-world needs become clear. What began as a few LED control commands turned into secure pairing, OTA updates, and a hardware redesign for rechargeable power. The key takeaway is that simple systems often expand once users start interacting with them, and having a flexible engineering partner makes those transitions smoother.
Ready to take the next step?
If you’re working on your own embedded project and want a partner who can help you handle both the quick wins and the unexpected pivots, get in touch with us today.
