---
type: concept
tags: [parking, architecture, readers]
sources: [parking-system-architecture]
updated: 2026-06-14
---

# Entry / Exit Readers

There are **two populations** of users, and they map to **two integration paths**. (See
[[parking-system-architecture]] §8.)

- **Permit holders / subscribers** — want hands-free/quick entry. Best served by reads reaching
  the **controller directly** ([[wiegand]]) so it can decide autonomously (works if host is down).
- **Casual / transient** — printed ticket, pay-on-exit, or plate recognition. Inherently
  **host-side** identity sources ([[lpr-camera]], QR/ticket scanner).

## How reads reach the system

| Reader type | Who sees the read | Decision by | Offline autonomy |
| --- | --- | --- | --- |
| [[wiegand]] reader → UHPPOTE port | The controller | Controller (onboard card list) | **Yes** — works if host down |
| Pure TCP/IP reader | Host only | Host, then UDP `open` to relay | No — host on critical path |
| [[lpr-camera|LPR]] / QR scanner | Host only | Host | No |
| **[[dingtian-dt008-reader|Dingtian DT-008]] QR reader** | Host only | Host (reads serial → `read` bus) | No |

> Concrete host-side reader on hand: the **[[dingtian-dt008-reader|Dingtian DT-008]]** (QR/RFID over HTTP push). Note autonomy
> is moot here anyway — the current relay ([[dingtian-relay]]) has **no onboard card list**, so even
> a Wiegand reader would be host-decided. So we take the serial/QR path straight to the host's
> `read` bus.

## Key points

- **Pure network readers are invisible to the [[uhppote-controller]]** — it only generates events
  for its own terminals. For a pure-TCP reader, only the host can listen/decide/command; the
  controller is demoted to a commanded relay (onboard card DB + offline autonomy bypassed).
- **Check for a Wiegand output first** — many "network" readers have both; wiring Wiegand in
  keeps autonomy + native event log.
- **Both models can share one relay** (valid Wiegand read **or** host `open` in "controlled"
  mode), so one lane serves permit + casual.
- **Each reader BINDS to a controller relay** (`config.controllerId` + `relay`) — the barrier it
  sits at — and inherits that relay's direction (entry/exit/both). An exit read opens exactly that
  relay; an entry read the entry relay. This is how separate in/out readers are disambiguated, with
  no "lane". See [[entry-exit-points]].
- **Host-in-the-loop is good for fraud detection** — two independent records (host's signed
  [[append-only-event-chain]] entry + the UHPPOTE remote-open event) should reconcile 1:1; any
  mismatch is an anomaly.

Autonomy caveat: with remote-host control enabled, the controller expects host comms every ~30 s
or reverts to local control (Wiegand-on-board lanes only).