LIAC - Low Intrusion (open) Access Control

Hey, y’all!

So, I’ve decided that the first project I’m planning on doing is a door access control system which I’m calling LIAC because naming things is fun :smiley: Here’s the current plan… I’ll update this as I progress, hopefully.

LIAC - Low Intrusion (open) Access Control

LIAC has a relatively unique design constraint: it should be able to be installed with as little modification as possible to the door frame, handle, and wall near the door that’s being access controlled, hence, low intrusion. The idea is that it should be able to be installed on rental properties with as little friction as possible.

The system is, for now, going to be focused on interior door access control, i.e. to a bedroom, office, etc. rather than to control an exterior door, which would likely require significantly more modification to be as secure as you’d want it to be. Still, a similar system might be viable with some modification, but that’s not the focus (at least for now). Secondary design goals are to be low cost and use readily available hardware and software while still retaining a relatively high level of security.

Of course, residential interior doors and frames are often going to be vulnerable to brute force physical attacks, but this system should try to reasonably thwart the most common physical and electrical bypass techniques (latch slipping, under/over door attacks, “hotwiring”/wire shorting, data wire sniffing) to serve as a deterrent in the event of a break-in: the vast majority of break-ins last less than 10 minutes, and commonly less than 5, so all we need to do here is not get owned by the lowest common denominator of effort.

High-level system overview

The system is designed to work with HF NFC chips, especially the xDF2/DESFire 2 based chips (it should be relatively trivial to make it work with most 13.56 MHz NFC chips as well, though). The system will be based around controlling an electric strike for access control, and is split into two primary parts: the reader and the controller.


The reader will be a self-contained, custom-designed circuit board and enclosure that goes on the outside of the door. It will contain a PN532 NFC controller and an nRF52810 SoC which will provide encrypted wireless communication to the controller through Bluetooth Low Energy. This will allow the reader to be affixed in a non-destructive manner to a wall or directly onto the outside of the door and will provide secure communication to the controller on the secure side of the door. It will be battery-powered, probably by standard AA or AAA batteries that are easy to replace if they die and should provide power for a long period of time before needing to be replaced.


The controller goes on the secure side of the door and will be in charge of actually controlling the strike. It will be wall-powered and the brains will be a Raspberry Pi Zero W. It will receive data from the reader wirelessly, and will be running a piece of software using libnfc to figure out what to do with the data the reader sends it and decide how to control the strike accordingly.


That’s all for now. Next, I will go into some more detail about the design of both controller and reader as I work it out. Been researching a bunch towards designing the reader PCB, which is really the “fun part” of the project for me as it will be my first custom PCB design :slight_smile:


This sounds awesome, you have all the ease of use requirements spot on while maintaining good levels of security and manufacturability in mind. Great job ideating so far!

I have experience training people on PCB Design and I love helping out with cool project so feel free to ping me if you want to chat. I’m pretty active on the Discord and there’s robust voice/video chat built in with screen sharing.

Devilclarke and I have also been working on a breakout for the PN7462 which is similar but more powerful than the PN532 if you end up needing it for the more advanced DESFire commands, and we could share some insights. You might not, in which case the PN532 is an excellent choice. Same for the Nordic chip, good call. I have the nRF52840 dongle and the nRF528432 eval board so I could test some stuff out if you need.



I have experience training people on PCB Design and I love helping out with cool project so feel free to ping me if you want to chat. I’m pretty active on the Discord and there’s robust voice/video chat built in with screen sharing.

Ooh, thanks for the offer, I will definitely hit you up if I’m confused on anything (which I likely will be hahaha).

Also, the PN7462 looks interesting but the PN532 already seems like a fair bit overkill for this purpose heh… One question I do already have is whether I’m just bad at finding/reading datasheets or if there’s basically no practical application/circuit design notes in the PN532’s datasheets… At this point, I’m basically relying on the schematics available from existing breakout board designs rather than anything from the manufacturer (thankfully Adafruit’s especially is very open and helpful design-wise)…

There’s one issue you’ll find with a lot of these more advanced ICs is that the valuable information is only available if you make an account with them as a business. The “short data sheets” available publicly don’t have all the necessary information, and the real example circuits and such often aren’t even found in the full datasheet, they’re squirrelled away in “application notes” and such. In the industry they intend for you to contact your personal application engineer if you hit any snags so they don’t expect you to be self sufficient like we would need.

I think you’re on the right track looking at reference designs where you can find them, and if you need any more info you can post here and someone will help you figure it out. I can’t really provide anything concrete because I’m under NDA, but I know several people around here are “under NDA” and may be able to help out one way or another.

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Aha, I see, that makes sense but is unfortunate for us plebian self-taught open-source hardware people hah. Wonder what the screening process is like for an account, maybe I could register with my LLC :thinking:

Guess we’ll cross that bridge when/if we come to it :stuck_out_tongue: