R4CVA02: Mini 2-Channel Analog Input Module with RS485 Modbus RTU

R4CVA02 is an ultra-compact, two-channel analog input acquisition module designed to measure external voltage or current signals and transmit the measurement data to a host controller through an RS485 interface.

Supporting Modbus RTU communication, the R4CVA02 enables PLCs, industrial computers, embedded systems, and monitoring applications to collect analog sensor data using standard serial commands.

The module is available in different hardware versions for voltage or current measurement, with different power supply options. Depending on the selected version, it can acquire 0–5 V, 0–10 V, 0–20 mA, or 4–20 mA signals.

Its miniature PCB design makes the R4CVA02 particularly useful for embedded projects where installation space and cost are important considerations.

2. Key Features

  • Two analog input channels: Monitor two independent analog signals.

  • Multiple input versions: Select voltage measurement or current measurement according to the application.

  • Voltage measurement: Supports compatible 0–5 V and 0–10 V sensor signals.

  • Current measurement: Supports compatible 0–20 mA and 4–20 mA transmitters.

  • RS485 communication: Suitable for remote data acquisition and distributed monitoring.

  • Modbus RTU protocol: Compatible with supported PLCs, PCs, and embedded controllers.

  • 12-bit ADC: Converts analog input signals into digital measurement data.

  • Fine measurement increments: Reports voltage or current values in units of 0.01 V or 0.01 mA, depending on the version.

  • Calibration support: Allows calibration to improve measurement accuracy when required.

  • Flexible power supply: Available in 4–5.5 V DC and 6–25 V DC versions.

  • Ultra-compact design: Approximately 30 × 15 × 3.5 mm.

  • Multi-device networking: Supports up to 247 devices in Modbus command mode, subject to addressing and network conditions.

3. Technical Specifications

Parameter Specification
Model R4CVA02
Module type 2-channel analog input acquisition
Number of channels 2
Voltage input versions 0–5 V / 0–10 V
Current input versions 0–20 mA / 4–20 mA
Voltage measurement range 0–11 V
Current measurement range 0–21 mA
ADC resolution 12-bit
Reported measurement increment 0.01 V / 0.01 mA
Manufacturer-stated accuracy Approximately 0.5%
Power supply options DC 4–5.5 V or DC 6–25 V
Operating current Approximately 9–13 mA
Communication interface RS485
Communication protocol Modbus RTU
Read function codes 03 / 04
Write function codes 06 / 16
Dimensions Approximately 30 × 15 × 3.5 mm
Weight Approximately 2 g

Specifications are based on the manufacturer's published product information. Input ranges, supply requirements, and measurement performance depend on the selected hardware version. Confirm the current manual before integration.

4. How the R4CVA02 Works

The R4CVA02 measures an external analog signal and converts it into digital data using its analog-to-digital converter (ADC). The resulting measurement can then be requested by a Modbus RTU master over the RS485 bus.

A typical installation consists of:

  1. An analog sensor or transmitter.

  2. The Eletechsup R4CVA02 module.

  3. An RS485-to-USB adapter, PLC, or embedded controller.

  4. Software that reads, displays, records, or processes the measurements.

For example, a voltage-version module can monitor two compatible voltage-output sensors. A current-version module can acquire two compatible industrial current-loop signals.

The host controller periodically reads the measurement registers and converts the values into meaningful engineering units where necessary.

Important: The voltage and current input types are hardware-version dependent. Do not assume that a single module can accept all voltage and current signal types simultaneously.

5. GitHub Integration: Home Assistant and Modbus RTU

One practical advantage of the R4CVA02 is its documented inclusion in the public GitHub project ha-modbus-manager.

GitHub repository: arturmietek/ha-modbus-manager

This project provides a Modbus RTU integration for Home Assistant, including a shared device library and YAML-based device definitions. Its device library includes an R4CVA02 definition for two-channel voltage acquisition.

Potential Home Assistant Applications

The R4CVA02 can serve as an analog data acquisition interface for a Home Assistant installation when the hardware version, register mapping, and software configuration are compatible.

Possible applications include:

  • Monitoring voltage-output sensors.

  • Displaying analog measurements on a dashboard.

  • Logging measurement history.

  • Triggering automations when sensor readings cross configured thresholds.

  • Integrating analog measurements into a larger Modbus monitoring network.

For example, a compatible voltage sensor could be connected to one input channel, and Home Assistant could display the acquired measurement as a sensor entity.

The exact configuration should be taken from the repository's current device definition and checked against the manufacturer's register documentation.

Typical Integration Workflow

  1. Connect the R4CVA02 to a suitable RS485 adapter or Modbus gateway.

  2. Confirm the module's supply voltage, slave address, and serial communication settings.

  3. Install or configure the Home Assistant Modbus integration.

  4. Use the repository's device definition as a reference.

  5. Verify the register addresses, scaling, and returned values against the hardware.

  6. Confirm that the displayed readings match the actual input signals.

GitHub reference: https://github.com/arturmietek/ha-modbus-manager

6. Python Integration for Custom Applications

Developers who prefer to build their own applications can use Python and a Modbus RTU library to read measurements from the R4CVA02.

The GitHub repository ul-gh/cheap_modbus_rtu provides another useful starting point for Eletechsup Modbus hardware integration.

A generic Python example using PyModbus is shown below:

from pymodbus.client import ModbusSerialClient

client = ModbusSerialClient(
    port="/dev/ttyUSB0",
    baudrate=9600,
    parity="N",
    stopbits=1,
    bytesize=8,
    timeout=1
)

if client.connect():
    # Illustrative example only.
    # Verify the actual register address,
    # function code and quantity in the
    # R4CVA02 communication manual.
    response = client.read_holding_registers(
        address=0,
        count=2,
        device_id=1
    )

    if not response.isError():
        print(response.registers)

    client.close()

This example illustrates the general serial communication workflow; it is not a verified, ready-to-run R4CVA02 register-reading script. The register address, quantity, slave ID, baud rate, and function code must match the actual module configuration and protocol documentation.

Depending on the register map, input measurements may need to be read using function code 04 or function code 03. The software must use the correct function code and data scaling for the selected version.

Once communication is established, the application can process the measurements, save them to a database, or forward them to a dashboard or monitoring service.

7. Practical Applications

Industrial Sensor Monitoring

The R4CVA02 can collect analog signals from compatible industrial sensors and make the readings available to a PLC or computer. This is useful for projects requiring a small number of analog input channels without a full-size I/O rack.

Pressure, Flow, and Level Measurement

Many industrial transmitters provide a 4–20 mA output. The current-input version can acquire compatible transmitter signals for monitoring pressure, flow, liquid level, and other process variables.

The host software can convert the measured current into the corresponding engineering value using the sensor's configured range.

For a linear 4–20 mA transmitter, the normalized measurement is:

[
\text{Fraction}=\frac{I-4}{20-4}
]

where (I) is the measured current in milliamps. The fraction can then be applied to the sensor's rated measurement range.

Voltage Signal Acquisition

The voltage-input version is suitable for compatible 0–5 V and 0–10 V sensors, analog outputs, and control signals.

It can be used in data logging, equipment monitoring, and embedded measurement systems where the voltage signal falls within the module's supported range.

Smart Home and Building Automation

Combined with a compatible RS485 interface and software such as Home Assistant, the module can provide analog measurements for custom building monitoring and automation projects.

Embedded Systems and OEM Equipment

Its miniature dimensions make the R4CVA02 suitable for integration into custom circuit boards, compact monitoring devices, and OEM equipment where board space is limited.

8. Why Choose Eletechsup R4CVA02?

The R4CVA02 offers a compact and economical way to add two analog input channels to an RS485-based control or monitoring system.

Its key benefits include:

  • Two-channel analog acquisition in a very small PCB footprint.

  • Separate voltage and current input versions.

  • Modbus RTU communication for compatible industrial controllers.

  • Flexible power supply options.

  • Public GitHub references for software integration.

  • Suitability for embedded applications and cost-sensitive monitoring projects.

Before selecting the module, engineers should verify the input type, power supply version, measurement accuracy, electrical isolation requirements, register mapping, and wiring arrangement.

Conclusion

The Eletechsup R4CVA02 is a miniature two-channel analog input module designed for voltage or current measurement over an RS485 Modbus RTU connection.

Its compact form factor and multiple hardware versions make it useful for sensor monitoring, industrial automation, embedded data acquisition, and smart home integration. The public GitHub project ha-modbus-manager provides a practical reference for integrating the voltage-input version with Home Assistant, while Python-based Modbus libraries offer a foundation for custom monitoring applications.

For developers and equipment manufacturers seeking a low-cost analog acquisition interface, the R4CVA02 provides a simple bridge between external analog sensors and software-based monitoring systems.

Official product information: Eletechsup R4CVA02

GitHub — Home Assistant Modbus integration: https://github.com/arturmietek/ha-modbus-manager

GitHub — Python Modbus RTU library: https://github.com/ul-gh/cheap_modbus_rtu

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