Hotel Card Reader Wiring: RFID Presence Detection and KNX Door Logic
Hotel room presence detection in a KNX system depends on a deceptively simple component: the wall-mounted card switch. Getting the wiring, ETS6 parameters and failsafe logic right determines whether the HVAC economy mode and DND/MUR indicators work reliably — or create guest complaints and false housekeeping dispatches. This guide covers card switch wiring, ETS6 input parameters, PIR supplement, door lock interfaces and multi-floor topology for hotels of 50 to 200 rooms.
Hotel card switch function
The hotel card switch is a wall-mounted holder, usually positioned near the room entrance, that accepts the guest's key card. The switch contains a simple mechanical or reed contact that closes when a card is inserted into the holder. In KNX context, this contact serves exclusively as a presence indicator — it tells the building management system whether a card (and by proxy, a guest) is present in the room.
RFID card reader vs card switch: the card reader in the hotel room door lock (VingCard, ASSA Abloy, Dormakaba) uses RFID/NFC technology to authenticate the card against the lock controller. This is completely separate from the wall-mounted card switch holder inside the room. The card switch is a passive contact — it has no RFID capability, does not identify the card, and does not communicate with the lock system. It simply detects card presence by contact closure. The terms are often confused in hotel specifications; clarify which component is meant in every project document.
Card switch brands (all compatible)
- Orbita (China, OEM for many hotel suppliers)
- Salto Systems card holder (separate from lock)
- VingCard wall holder (separate from door lock)
- Dormakaba room card holder
- Generic hotel card switch (2-wire NO contact)
- All use identical 2-wire normally-open contact output
Electrical characteristics
- Contact type: normally open (NO)
- Card inserted: contact closed (resistance <1Ω)
- Card removed: contact open (resistance >1MΩ)
- Max switching voltage: 24V DC (KNX binary input safe)
- Max switching current: 100mA (well within KNX input range)
- Cable: 2-core 0.5mm² signal cable sufficient
Card switch wiring to KNX binary input
The card switch contact is wired to a KNX binary input module. The binary input provides the contact sensing circuit (typically 12–24V DC internally) and converts the contact state to a KNX telegram. No external power supply is needed for the card switch itself.
Card switch wiring diagram
Card switch holder (wall-mounted, near entrance):
Terminal A → 2-core signal cable → KNX binary input IN1+
Terminal B → 2-core signal cable → KNX binary input IN1−
Cable specification:
Type: 2-core 0.5mm² PVC signal cable
Route: In conduit from floor distribution box to room
Length: Max 100m from KNX binary input to card switch
(KNX input internal circuit; verify with manufacturer)
Screen: Not required for card switch signal
KNX binary input modules (suitable):
ABB M2184.1 — 4-channel binary input, DIN rail
MDT BE-0800.01 — 8-channel binary input, DIN rail
Schneider MTN6755-0001 — 6-channel binary input, DIN rail
All located in floor distribution board, not in room
KNX bus cable (YCYM 2×0.8mm²) from distribution board to room
Signal cable (2×0.5mm²) from distribution board to card switchCentral vs distributed binary input:locating the KNX binary input in the floor distribution board (rather than in the room) allows the room to contain only the MDT SCN-RT55P and its 2 relay outputs. The binary input for card switch, DND button and MUR button can be in the distribution board, with signal cables running to the room. This simplifies in-room wiring but requires more cable runs. Alternatively, the SCN-RT55P's four integrated inputs eliminate the need for a separate binary input device.
ETS6 binary input parameters for card switch
The ETS6 parameters for the card switch input are critical to reliable operation. Two timing parameters prevent false economy mode activation during normal guest behaviour: the activation delay (debounce) and the deactivation delay (hold-on after card removal).
ETS6 binary input — card switch parameters
Input channel: Card switch (Input 1 on SCN-RT55P or binary input)
Input type: Contact (not push-button, not dimmer)
Contact type: Normally open (NO)
Polarity: Active = contact closed (card inserted)
Activation delay: 3 seconds
(debounce — prevents spurious activation from contact
bounce on card insertion; 3s is sufficient)
Deactivation delay: 180 seconds (3 minutes)
(hold-on after card removed — prevents HVAC economy
and lights-off during brief card absence; see rationale)
On activation (contact closes):
Object: Presence GA (10/room/0) DPT 1.002 = 1
Additional: trigger scene 1 (welcome) via GA 10/room/5
On deactivation (after 180s delay):
Object: Presence GA (10/room/0) DPT 1.002 = 0
Additional: trigger scene 2 (eco) via GA 10/room/5
Cyclical sending: Every 600 seconds (10 minutes)
(heartbeat — BMS can detect if KNX device has failed)
Send current state cyclically regardless of changeWhy 180 seconds?
Hotel guests remove their card from the holder for many reasons: to use the card at the minibar (if RFID), to check the card number, or when fumbling at the door on return. A 60-second delay is too short and results in HVAC cycling. 180 seconds covers most normal removal scenarios. For premium hotels, 300 seconds (5 minutes) is used. Do not exceed 600 seconds or the eco mode will never activate after legitimate absence.
Cyclical sending purpose
Sending the current presence state every 10 minutes allows the BMS or PMS middleware to detect KNX device failures. If GA 10/room/0 has not been updated for 20+ minutes despite the room being occupied, a fault flag is set. This is essential for 200-room hotels where a failed KNX device might otherwise go undetected for hours.
Card switch vs dedicated occupancy sensor
A card switch detects card presence, not actual room occupancy. These are not always the same: a guest may leave the room without removing the card, or a maintenance engineer may be in the room with no card inserted. For better energy management and genuine occupancy detection, supplement the card switch with a PIR (passive infrared) occupancy sensor.
| Scenario | Card switch | PIR sensor | Combined logic |
|---|---|---|---|
| Guest in room, card inserted | Presence = 1 | Occupied = 1 | Comfort mode — correct |
| Guest left, card still in holder | Presence = 1 (wrong) | Occupied = 0 (correct) | OR logic: comfort mode continues — acceptable (card left = guest intends to return) |
| Guest in room, card in pocket | Presence = 0 (wrong) | Occupied = 1 (correct) | OR logic: comfort mode — correct |
| Room empty, card left | Presence = 1 (wrong) | Occupied = 0 (correct) | OR logic: comfort mode — inefficient (card forgotten) |
| Maintenance, no card | Presence = 0 | Occupied = 1 | OR logic: comfort mode — correct for staff comfort |
ETS6 OR logic — card switch + PIR
KNX PIR sensor (ceiling mount): Elsner P03/2 KNX or BEG PD9-KNX — Send occupied = 1 on motion detected — Hold occupied = 1 for 5 minutes after last motion — GA 10/room/8 DPT 1.002 (PIR presence) ETS6 logic block (OR gate): Input A: GA 10/room/0 (card switch presence) Input B: GA 10/room/8 (PIR presence) Output: GA 10/room/9 DPT 1.002 (combined occupancy) Logic: Output = 1 if A=1 OR B=1 HVAC setpoint driven by GA 10/room/9 (combined), not directly by card switch GA 10/room/0. PIR absent for 5 min AND card switch absent for 180s: → Combined occupancy = 0 → HVAC economy mode
Electronic door lock interface
Hotel RFID door locks use their own communication protocol between the card reader and the lock controller — typically Wiegand 26-bit or OSDP. This protocol is not KNX and is not connected to the KNX bus. The door lock communicates with the access control system (ACS), not the building automation system. However, door lock status (door open/closed, lock engaged/disengaged) can be fed into KNX via dry contact outputs from the lock controller.
Door lock to KNX wiring
RFID lock controller outputs (dry contacts):
Door status (NO/NC relay): door open = contact closed
→ Wire to KNX binary input → GA 10/room/7 DPT 1.002
Lock override input (dry contact from KNX):
Reception unlock → KNX binary output relay → lock override
KNX binary output → relay (30VDC/0.5A) → lock override input
GA 10/room/11 DPT 1.001 = 1 → relay on → door unlocked (3s pulse)
Wiegand reader cable (reader to lock controller):
4 conductors: D0 (green), D1 (white), GND (black), +12VDC (red)
Max cable length: 30m from reader to controller (Wiegand specification)
Over 30m: use OSDP instead of Wiegand (RS485, up to 150m)
Cable: shielded 4-core 0.5mm² (screen to GND at controller end only)
OSDP (Open Supervised Device Protocol):
RS485 2-wire (A/B) + GND + 12VDC
Max length: 150m (RS485 at 9600 baud)
Bi-directional: reader can send LED/buzzer commands
Preferred for new installations (supervised, tamper detection)Do not confuse door lock Wiegand with KNX bus: Wiegand and OSDP cables are access control cables, not KNX bus cables. They must be routed separately from the KNX YCYM 2×0.8mm² bus cable. Routing access control cables parallel to KNX bus in the same conduit without separation can cause interference in OSDP RS485 systems. Maintain minimum 50mm separation or use screened conduit for access control cable runs longer than 10m adjacent to KNX bus cable.
DND and MUR indicator wiring at room door
The DND (Do Not Disturb) and MUR (Make Up Room) LED indicators are mounted in the door face insert or beside the room door. They require a DC supply voltage and are switched by the KNX binary output relay in the room controller or distribution board.
DND/MUR LED wiring
DND LED (red): door face insert LED indicator
Supply: 12V DC SMPS (e.g., Mean Well HDR-15-12, 15W DIN rail)
Wiring: 12VDC SMPS output → KNX relay output 1 (NO) → DND LED +
LED − → GND (common with SMPS GND)
Cable: 2-core 1.0mm² (12VDC supply, max 50mA LED)
Control: GA 10/room/1 DPT 1.001 = 1 → relay closes → LED illuminated
MUR LED (green): door face insert LED indicator
Supply: Same 12V DC SMPS (or separate for EMC isolation)
Wiring: 12VDC SMPS output → KNX relay output 2 (NO) → MUR LED +
LED − → GND
Cable: 2-core 1.0mm²
Control: GA 10/room/2 DPT 1.001 = 1 → relay closes → LED illuminated
Alternative (230V relay → LED driver):
KNX switch actuator 230V relay output → LED driver module
LED driver: constant current 12VDC, IP20, DIN rail
Use when KNX switch actuator is only available in 230V version
LED driver converts 230V AC to 12VDC for LED supply
SCN-RT55P relay specification:
Relay outputs: 30VDC / 0.5A max
Use 12V DC SMPS + relay (not 230V directly into SCN-RT55 relay)EMC note for LED driver switching noise: LED drivers with switching regulators generate high-frequency noise that can cause false triggering on adjacent KNX binary inputs if cables are routed in parallel. Use screened cable for DND/MUR LED supply where the cable runs parallel to signal cables (card switch, DND button) for more than 1m. Ground the screen at one end only (at the distribution board, not at the LED). MDT recommends EMC screening near the SCN-RT55 to prevent LED driver switching noise coupling into binary inputs via shared conduit.
Room panel wiring schedule
A structured wiring schedule for the room panel prevents installation errors and simplifies fault-finding during commissioning. Document every cable, terminal and group address per room before site installation begins.
| Connection | Cable type | From | To |
|---|---|---|---|
| KNX bus | YCYM 2×0.8mm² | Floor distribution board (KNX line coupler) | MDT SCN-RT55P bus terminals |
| Card switch | 2×0.5mm² signal | Card holder wall mount (room) | SCN-RT55P Input 1 (or binary input IN1) |
| DND button | 2×0.5mm² signal | DND push-button (room) | SCN-RT55P Input 2 |
| MUR button | 2×0.5mm² signal | MUR push-button (room) | SCN-RT55P Input 3 |
| DND LED supply | 2×1.0mm² | 12VDC SMPS output | SCN-RT55P Relay 1 NO (to LED+) |
| DND LED return | 2×1.0mm² | DND LED − | 12VDC SMPS GND |
| MUR LED supply | 2×1.0mm² | 12VDC SMPS output | SCN-RT55P Relay 2 NO (to LED+) |
| MUR LED return | 2×1.0mm² | MUR LED − | 12VDC SMPS GND |
| Lock override | 2×1.0mm² | SCN-RT55P Relay 3 NO | Door lock controller override input |
Multi-floor commissioning strategy
Hotels with 50–200 rooms require a systematic KNX topology plan that allocates devices to lines, lines to floors, and floors to the backbone. Without this structure, the 64-device-per-line limit and 640mA power supply constraint cause problems at the commissioning stage that are expensive to rectify.
200-room hotel KNX topology
200 rooms ÷ 10 rooms per line = 20 KNX lines (one PS640 each)
KNX topology:
Backbone line (Area 0):
KNX IP router (Weinzierl 770 or MDT KNX IP Gateway)
Central control PC / middleware server
Area 1 (floors 1–5):
Line coupler (ABB LK/S 4.2) at each floor DB
Line 1.1: Floor 1 rooms 101–110
Line 1.2: Floor 1 rooms 111–120
Line 1.3: Floor 2 rooms 201–210
... etc.
Per-line device count (10 rooms, typical):
10× MDT SCN-RT55P (room controller) = 10 devices
10× KNX binary input 4-channel (card,DND,MUR,PIR) = 10 devices
10× KNX switch actuator 4-channel (DND LED, MUR, lock, spare) = 10 devices
10× KNX dimmer actuator = 10 devices
1× Line coupler (LK/S at floor DB) = 1 device
Total: 41 devices per line (well within 64-device limit)
Power supply per line:
PS640 (640mA): 41 devices × ~12mA average = ~492mA used
Margin: 148mA available for expansion
Group address count:
200 rooms × 12 GAs per room = 2,400 GAs
(ETS6 limit: 65,536 GAs — no concern)
Individual address scheme:
Area.Line.Device = Floor.RoomLine.DeviceInRoom
Room 101, controller: 1.1.1
Room 101, binary input: 1.1.2
Room 102, controller: 1.1.3
Room 201 (floor 2, line 1): 1.3.1Line coupler placement
- ABB LK/S 4.2 or MDT SCN-LC0400.01
- Mounted in floor distribution board (DB)
- One line coupler per floor segment
- Filters group telegrams — only forwards GAs defined in ETS6
- Isolates floor segment during commissioning
- Allows individual floor download without affecting others
Commissioning phasing
Commission one complete floor before moving to the next. Verify every room on each floor using a KNX bus monitor (ETS6 Group Monitor or dedicated tool). Test card switch, DND/MUR LEDs, HVAC gateway and PMS integration per room. Record pass/fail per room in commissioning log. Only when floor is fully verified, proceed to the next floor. This prevents systematic errors from propagating across all floors.
Cable routing and EMC guidelines
Hotel rooms have multiple electrical systems in close proximity: KNX bus, signal cables, LED driver supplies, HVAC control cables and Wiegand access control cables. Correct cable routing prevents electromagnetic interference (EMC) that causes false triggering on KNX binary inputs.
EMC cable separation rules
- KNX bus (YCYM 2×0.8mm²): minimum 100mm from 230V power cables
- KNX bus: minimum 50mm from LED driver supply cables
- Card switch signal cable: minimum 50mm from LED driver cables
- Wiegand access control cable: minimum 50mm from KNX bus
- Use separate conduits for KNX bus and power cables throughout
- If parallel routing exceeds 1m: use screened cable for signal circuits
- Screen grounded at one end only (distribution board end)
- OSDP RS485: shielded cable mandatory; screen at controller end
- Avoid routing KNX bus and OSDP cable in same conduit run
- Label all cables at both ends during installation (not after)
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