When One Network Closes, Another Opens

When you have a technological problem and no products on the market can quite solve it, what do you do? Most people would be inclined to grumble a bit, then choose the best available option and make do with its shortcomings. But those that are handy with a soldering iron and compiler are more likely to get busy solving their problem by building a prototype device that does exactly what they want it to do.

The prototyping wizards at Zalmotek definitely fall into the latter category, so when they found the access control system for their office to be lacking, they designed their own solution. Existing NFC card-based employee access systems work well enough in general, they noted, but they are typically very expensive. Worse yet, they rely on Wi-Fi to operate normally, so if the wireless network goes down, no one is getting in.

That might not be entirely bad because it is a good reason for an unexpected day off. But some things cannot wait, so creating a more robust access system is the right thing to do even if it does cost us an occasional day at the beach. Zalmotek chose to design their prototype around the Particle M-SoM platform, specifically a M524 SoM and M.2 SoM Evaluation Board. These are versatile boards that make it simple to rapidly build a device that incorporates both Wi-Fi and cellular connectivity. Should one network go down, there is always a backup plan at the ready.

The M-SoM board was connected to a DFRobot NFC module to allow it to read access cards. These access cards grant access to people on the outside of the door, while a PIR sensor is used to detect the presence of humans on the inside of the door — this allows it to unlock the door and let people leave without swiping a card. An electronic lock in the door was wired into the system to allow or deny access based on the code running on the M-SoM.

Generally there will be more than one access point in a building, so the team also leveraged Particle Cloud services to manage access credentials. In this way, the credentials can be updated in one place and immediately take effect everywhere — no need to manually update each access control point. Using these cloud services also allowed Zalmotek to log all access attempts, whether successful or not, to know who is coming and going, and if there are inappropriate attempts to enter the office.

The full project write-up gives details about building the circuit, adding the M-SoM to Particle Console, programming the device, and integrating with cloud services. A quick read can save you a lot of time if you are interested in building a similar system. And if this access control system meets your needs, it is worth noting that a custom circuit can be designed using the M-SoM module itself, which would make it much smaller than the prototype that uses the evaluation board.