The ComWinTop CWT-THxxx series are RS-485 Modbus RTU temperature and humidity sensors available in multiple probe form factors (CWT-TH01S through CWT-TH05S). The TapHome template reads temperature and relative humidity values and provides service actions for configuring the slave ID and baud rate directly from TapHome.
The sensors are powered by DC 5–30 V and communicate over RS-485 at distances up to 800 m, making them suitable for distributed building monitoring.
Hardware connection
Wiring
The sensor has a 4-wire cable:
| Cable Color | Function |
|---|---|
| Brown | Power + (DC 5–30 V) |
| Black | Power − (GND) |
| Yellow / Green | RS-485 A+ |
| Blue | RS-485 B− |
Connect the RS-485 A+ and B− wires to the corresponding terminals on a TapHome Modbus RTU gateway (e.g. TapHome Core RS-485 bus). The power GND and RS-485 GND should share a common ground.
Ensure proper grounding between the sensor and the Modbus gateway. Without a shared GND reference, communication errors are likely, especially on longer cable runs.
Specifications
| Parameter | Value |
|---|---|
| Power supply | DC 5–30 V, < 0.1 W |
| Temperature range | −30°C to +80°C (±0.5°C) |
| Humidity range | 0–100% RH (±5% RH) |
| Resolution | 0.1°C / 0.1% RH |
| Communication | RS-485 Modbus RTU |
| Max cable length | 800 m |
Configuration
Communication parameters
The TapHome template uses 9600 baud, 8 data bits, no parity, 1 stop bit. The factory default baud rate is 4800 bps — use the Set Baud Rate service action in TapHome (or a Modbus tool) to change it to 9600 before importing the template.
Alternatively, if you prefer to keep the factory 4800 baud rate, adjust the baud rate in the TapHome module connection settings after import.
Slave ID
The default slave ID is 1. When connecting multiple CWT-THxxx sensors on the same RS-485 bus, each sensor needs a unique slave ID (1–254). Use the Set Slave ID service action in TapHome to change the address.
Device capabilities
Temperature and humidity monitoring
The template exposes a single Temperature & Humidity Sensor device that reads:
- Temperature — ambient temperature in °C (register H:1, Int16, ÷10 conversion). Range −30°C to +80°C with 0.1°C resolution. Negative temperatures use two’s complement encoding.
- Humidity — relative humidity in %RH (register H:0, UInt16, ÷1000 conversion). Range 0–100% RH with 0.1% resolution.
Service diagnostics and configuration
The module provides two service attributes and two service actions for bus configuration:
- Slave ID (read from H:2000) — displays the current Modbus address
- Baud Rate (read from H:2001) — displays the current baud rate (2400, 4800, or 9600)
- Set Slave ID — writes a new address (1–254) to H:2000
- Set Baud Rate — writes a new baud rate selection to H:2001 (0 = 2400, 1 = 4800, 2 = 9600)
Additional capabilities
The CWT-THxxx sensors also provide calibration registers for temperature offset (H:0x0050) and humidity offset (H:0x0051) with 0.1°C / 0.1% RH resolution. These allow fine-tuning measurements without modifying the TapHome configuration. Calibration support can be added in a future template update.
Troubleshooting
No readings after import
- Verify the baud rate matches between the sensor and TapHome — the template expects 9600 bps but the factory default is 4800
- Check the RS-485 wiring: A+ to A+, B− to B−, shared GND
- Confirm the correct slave ID is set in the TapHome import parameters
Incorrect humidity values
The template uses a ÷1000 scale factor for the humidity register, as defined in the XML template. If readings appear off by a factor of 100, this may indicate a firmware variation. The XML template is the authoritative source for the TapHome integration.
Communication errors on long cable runs
- Ensure a shared GND connection between the sensor and the gateway
- Use twisted-pair cable for the A+/B− lines
- Add a 120 Ω termination resistor at the end of the bus if the cable exceeds 100 m
