R4DCB08 Temperature Sensor Utility

V1.13 (2026-01-28)

A command-line utility for communicating with R4DCB08 temperature sensor modules via serial port.

Overview

This utility allows you to:

• Read temperature data from up to 8 channels in real-time
• Configure device settings (address, baudrate)
• Read and set temperature correction values
• Monitor temperature with configurable intervals

Installation

Prerequisites

• C compiler (GCC/Clang)
• Make utility
• Serial port support (Linux/Unix-based systems)

Compilation

make

System-wide Installation (optional)

sudo make install    # Installs to /usr/local/bin
sudo make uninstall  # Removes from /usr/local/bin

Quick Start

1. Connect the R4DCB08 module to your computer via USB-RS485 adapter
2. Run the utility:

./r4dcb08

Example output (reading 4 channels every 2 seconds):

$ ./r4dcb08 -n 4 -t 2
# Date                  Ch1  Ch2  Ch3  Ch4
2026-01-21 14:30:15.42  22.5 23.1 21.8 22.0
2026-01-21 14:30:17.42  22.6 23.0 21.9 22.1
2026-01-21 14:30:19.42  22.5 23.1 21.8 22.0
^C
Received SIGINT (Ctrl+C), measurement stopped

Output format: timestamp Ch1 Ch2 Ch3 ... - channels are printed in order from 1 to n, separated by spaces.

Press Ctrl+C to stop continuous measurements.

Usage

Basic Examples

1. Read temperature from channel 1 (default):

./r4dcb08

2. Read 4 channels every 2 seconds:

./r4dcb08 -n 4 -t 2

3. Single measurement without timestamp (useful for scripts):

./r4dcb08 -n 4 -f
# Output: 22.5 23.1 21.8 22.0

4. Use different serial port:

./r4dcb08 -p /dev/ttyUSB1

5. Enable median filter (smooths out noise/spikes):

./r4dcb08 -m

6. Enable MAF filter (moving average with trapezoidal weights):

./r4dcb08 -M 5

7. Combine filters (median → MAF pipeline):

./r4dcb08 -m -M 5 -n 4 -t 2

Digital Filters

The utility provides two digital filters that can be used separately or combined:

Median Filter (-m)

• Three-point median filter
• Removes isolated spikes while preserving signal edges
• Introduces 1 sample delay

MAF Filter (-M n)

• Moving Average Filter with trapezoidal weights
• Window size n must be odd (3, 5, 7, ... 15)
• Weights: [0.5, 1, 1, ..., 1, 0.5]
• Formula: MAF = (0.5·x[0] + x[1] + ... + x[n-2] + 0.5·x[n-1]) / (n-1)
• Smooths high-frequency noise while reducing edge distortion compared to simple moving average

Filter Workflow

When both filters are enabled, data flows through the pipeline:

Raw data → Median Filter → MAF Filter → Output

Example with 4 channels, 2-second interval, median + MAF(5):

$ ./r4dcb08 -m -M 5 -n 4 -t 2
# Active three-point median filter for all data ...
# Active MAF filter (window size 5) for all data ...
#
# Date                  Ch1  Ch2  Ch3  Ch4
2026-01-28 10:15:03.12  22.5 23.1 21.8 22.0
2026-01-28 10:15:05.12  22.5 23.0 21.9 22.0
2026-01-28 10:15:07.12  22.5 23.1 21.8 22.0
^C
Received SIGINT (Ctrl+C), measurement stopped

Device Configuration

8. Read current temperature correction values:

./r4dcb08 -c

9. Set temperature correction for channel 3 to +1.5°C:

./r4dcb08 -s 3,1.5

Temperature correction is useful when sensor readings need calibration (e.g., sensor shows 21.0°C but actual temperature is 22.5°C → set correction to +1.5).

10. Change device address from 1 to 5:

./r4dcb08 -a 1 -w 5

Note: -a 1 specifies current address, -w 5 sets new address.

11. Change device baudrate to 19200:

./r4dcb08 -x 4

Baudrate codes: 0=1200, 1=2400, 2=4800, 3=9600, 4=19200. Change takes effect after device power cycle.

12. Factory reset:

./r4dcb08 -r

Writes factory defaults to EEPROM (address 1, baudrate 9600, all corrections 0). Power cycle needed to apply.

13. Scan RS485 bus for devices:

./r4dcb08 -S

Scans addresses 1-254 and reports all responding devices. Useful for discovering device addresses on the bus.

Example output:

Found 2 device(s):
  1
  15

Command Line Options

Option	Description	Default
-p [port]	Serial port device	/dev/ttyUSB0
-a [1-254]	Device address (for multi-device setups)	1
-b [baud]	Serial port baudrate {1200, 2400, 4800, 9600, 19200}	9600
-t [seconds]	Interval between measurements	1
-n [1-8]	Number of channels to read	1
-c	Read temperature correction values	-
-w [1-254]	Write new device address	-
-x [0-4]	Write device baudrate (0=1200, 1=2400, 2=4800, 3=9600, 4=19200)	-
-s [ch,value]	Set temperature correction for channel (e.g., -s 3,1.5)	-
-m	Enable three-point median filter (reduces noise)	Off
-M [3-15]	Enable MAF filter with window size (must be odd)	Off
-f	One-shot measurement without timestamp	Off
-r	Factory reset (resets to address 1, baudrate 9600, corrections 0)	-
-S	Scan RS485 bus for devices (addresses 1-254)	-
-h or -?	Display help	-

Understanding -b vs -x

• -b sets baudrate for this session (how fast your computer talks to the device)
• -x changes baudrate stored in the device (permanent, survives power cycle)

Normally you only need -b if default 9600 doesn't work. Use -x only when you want to permanently change device speed.

Notes

• Temperature readings are in degrees Celsius
• Valid range: -55.0°C to 125.0°C (values outside show as NaN)
• Press Ctrl+C to stop continuous measurements
• Multiple devices can share one RS485 bus using different addresses

MQTT Daemon

For continuous monitoring and integration with home automation systems, there's a separate MQTT daemon that publishes temperature readings to an MQTT broker.

Features:

• Publishes temperatures to MQTT broker (Mosquitto, etc.)
• TLS/SSL support
• Runs as systemd service or standalone
• Auto-reconnect, LWT for offline detection
• Works on systems without systemd (Alpine, FreeBSD)

Quick example:

cd mqtt_daemon
make
./r4dcb08-mqtt -p /dev/ttyUSB0 -H mqtt.local -v

See mqtt_daemon/README.md for full documentation.

Changelog

V1.13 (2026-01-28)

• Added MAF (Moving Average Filter) with trapezoidal weights (-M option)
• Window size configurable (odd values 3-15)
• Filters can be chained: median → MAF

V1.12 (2026-01-28)

• Minor code improvements

V1.11 (2026-01-23)

• Added RS485 bus scan feature (-S option)
• Scans addresses 1-254 with 100ms timeout per address
• Reports all responding Modbus RTU devices

V1.10 (2026-01-21)

• Added factory reset command (-r option)
• Resets device to address 1, baudrate 9600, all corrections 0

V1.9 (2026-01-21)

• Replaced deprecated signal() with POSIX sigaction()
• Removed unsafe printf() from signal handler
• Added NULL check after now() call
• Replaced usleep() with POSIX nanosleep()
• Fixed type punning using portable bitwise operations

V1.8 (2025-08-29)

• Added exclusive file locking (flock) for serial port
• Improved reliability in multi-process environments

V1.7 (2025-06-06)

• Unified error handling system
• Centralized constants
• Fixed resource leak in port initialization

V1.6 (2025-06-06)

• Fixed baud rate table bug (1200 baud)
• Code cleanup and optimization

V1.5 (2025-04-17)

• Implemented AppStatus error codes
• Modularized configuration
• Improved signal handling

V1.4 (2025-04-14/16)

• Added median filter
• Enhanced input validation

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Technical Reference

This section is for developers and advanced users.

Protocol

Modbus RTU over serial port:

• Function 0x03: Read holding registers
• Function 0x06: Write single register

Register Map

Register	Description	R/W	Values
0x0000-0x0007	Temperature readings (channels 1-8)	R	signed int16 / 10
0x0008-0x000F	Temperature correction values	R/W	signed int16 / 10
0x00FD	Automatic report interval	R/W	0-255 (seconds, 0=disabled)
0x00FE	Device address	R/W	1-254
0x00FF	Baudrate setting	R/W	0-4 (see codes below)
0x00FF	Factory reset	W	5 (triggers reset)

Baudrate codes: 0=1200, 1=2400, 2=4800, 3=9600, 4=19200

Factory reset: Writing value 5 to register 0x00FF writes default values to EEPROM (address=1, baudrate=9600, corrections=0). Power cycle needed to load new settings from EEPROM.

Error Codes

• 0: Success
• -10 to -19: Argument errors
• -20 to -29: Communication errors
• -30 to -39: Operation errors