How the gates work

Each gate has one or more lanes: in, out or both, and either guarded (a guard checks visitors on the gate phone) or unmanned (a gate controller decides and raises the barrier).

The gate controller

A small box at the gate — a Raspberry Pi 4 or 5, or any small x64 computer — wired to the barrier relays and the readers on its lanes. It:

Decides on its own, from a copy of the estate’s passes, residents, vehicles and rules that it refreshes every five minutes and whenever something changes. The gate keeps working when the internet does not.
Checks typed codes, QR passes, residents’ own QR codes, eight-digit offline codes, tag numbers and number plates, with the same rules as the gate phone: dates and hours, entries, in or out, the watchlist, emergencies.
Remembers every decision and uploads it to the estate’s gate log as soon as it can.
Reports every minute: its clock, what is waiting to upload, software version, keypad states and the enclosure’s tamper switch.
Obeys remote commands (open a lane, turn a keypad back on, sync now) only when they are signed by the estate.

What it reads

Reader	Connects by	Lets in
USB keypad or QR scanner	USB (types like a keyboard)	Visitor codes, QR passes, residents’ QR, offline codes
Wiegand card reader or keypad	GPIO (DATA0/DATA1)	Residents’ tags and cards; codes typed and sent with `#`
Number-plate (ANPR) camera	The estate’s network	Approved resident cars; visitors booked with that plate

More than one gate

Controllers at the same estate tell each other what they let in over the estate’s own network — the estate hub. A single-use code or an offline code used at one gate is refused at another, even during an internet outage. There is no extra box: each gate keeps working on its own if the others are down.

When a controller goes quiet

The estate’s security admins are alerted if a controller has not been heard from for 24 hours.