Milesight UC100: Bring Modbus Devices to the Cloud via LoRaWAN

Many companies have machines, meters and equipment that could deliver data, yet they stay silent. The reason is almost always the same: they speak Modbus over an RS485 line, sit on a wired bus and have no direct path to the cloud.

The Milesight UC100 is a small device that closes exactly this gap. It reads Modbus data and forwards it via LoRaWAN, without pulling a single new data cable. This article explains how the UC100 works and what it enables in operation.

Table of Contents

• The problem: Modbus data is stuck on the wire
• What is the Milesight UC100?
• How the UC100 works, step by step
• A practical example: reading an electricity meter's active power
• From device to cloud: the architecture
• What the UC100 makes possible
• Honest limits
• Context: alternatives and scope
• merkaio: retrofit from a single source
• Sources

The problem: Modbus data is stuck on the wire

Modbus is an open industrial protocol, first published in 1979 by Modicon (today part of Schneider Electric) and still a de-facto standard today ^[4][5]. It is vendor-neutral, royalty-free and simple, which is why countless devices still speak it.

The most common variant in the field is Modbus RTU, a compact serial transmission with a CRC checksum that usually runs over RS485 ^[5]. Functionally, Modbus follows a simple polling principle: a master (the Modbus Organization now uses the terms client and server) queries the connected devices one after another, each via a bus address in the range 1 to 247 ^[4][5]. The readings sit in 16-bit registers that the master reads out.

What speaks Modbus RTU? In practice, a lot: energy and electricity meters, power analysers, PLCs, variable frequency drives, inverters, HVAC and refrigeration controllers, PV inverters, plus flow and level sensors ^[5]. The catch: RS485 is a wired, serial bus. The devices have no IP address of their own, a cable run reaches around 1200 metres, and there is no direct path to the internet ^[5]. Anyone who wants this data in a cloud or dashboard needs a bridge.

What is the Milesight UC100?

The UC100 is exactly that bridge: a Modbus-to-LoRaWAN converter ^[3]. According to the datasheet it reads up to 32 Modbus RTU devices and supports up to 32 Modbus registers or channels ^[1][2]. (A note on diligence: the product page sometimes states "64 registers", but the technical datasheet and the user guide consistently say 32. Plan with the datasheet value.)

The key specs from the datasheet ^[1]:

• Modbus side: one RS485 interface via a 2-pin 3.5 mm terminal block, baud rates from 1200 to 115200 bps, a switchable 120-ohm termination resistor. It supports Modbus RTU and a passthrough mode.
• Radio side: LoRaWAN in OTAA/ABP, Class C, with the bands EU868 plus CN470, IN865, RU864, US915, AU915, KR920 and AS923. Transmit power is 16 dBm in the 868 MHz band, sensitivity is -137 dBm.
• Form factor and power: a compact plastic housing (PC+ABS) at 70 × 45 × 13 mm and 32 g, IP30, operating temperature -20 to 60 °C. It is powered by DC 5 to 24 V or via USB Type-C (5 V/1 A) at under 0.5 W, with surge and reverse-polarity protection.

The UC100 comes in two variants: with an internal antenna and as the UC100 (EA) with an external SMA antenna ^[1]. Both are pure LoRaWAN devices. If you need cellular instead of LoRaWAN, Milesight has the separate UC300/UC500 line.

How the UC100 works, step by step

In operation, the UC100 acts as the Modbus master on the RS485 bus. The sequence:

1. Connect: the Modbus device is wired to the UC100 over RS485, and the bus is terminated via the 120-ohm switch.
2. Configure: using the USB Type-C port and the free Milesight ToolBox software, you define which registers are read at which interval ^[1][2]. Configuration also works remotely via LoRaWAN downlink, and firmware updates run over FUOTA.
3. Read and transmit: the UC100 polls the configured registers and packs the values into LoRaWAN uplinks. In passthrough mode it relays Modbus requests transparently.
4. Robustness: if the network drops, the UC100 stores up to 800 records locally and sends them later via data retransmission ^[1]. Through up to 16 IF-THEN rules and the Milesight D2D protocol it can even react autonomously, for example triggering threshold alarms, without a server in the loop ^[1][2].

Because the UC100 runs in LoRaWAN Class C, it is permanently ready to receive and responds quickly to downlinks. What the device classes mean in practice is covered in our post on the LoRaWAN classes A, B and C. Milesight states the UC100's own radio range as up to 2 km in cities and 15 km in rural areas ^[1].

A practical example: reading an electricity meter's active power

This gets concrete with a common example: an Eastron SDM630, a three-phase Modbus RTU DIN-rail energy meter. Here is how you connect its total active power:

1. Wire it: connect the SDM630's RS485 terminals (A/B) to the UC100's 2-pin RS485 port and terminate the bus with the 120-ohm switch.
2. Match the serial parameters: in ToolBox under the RS485 settings, enter the meter's values. Out of the box the SDM630 uses 9600 baud, 8 data bits, 1 stop bit, no parity and Modbus address 1 ^[10]. The UC100 and the meter must match exactly here.
3. Add a Modbus channel: configure one of the 32 channels: Slave ID 1, start address 0x0034 (register 30053, "Total system power" in watts), type "Input register / Float" and byte order ABCD ^[2][10]. The SDM630 returns measurements as 32-bit IEEE-754 floats across two registers, most significant register first, read with Function Code 04 ^[10]. The "Fetch" button tests the channel immediately.
4. Set the interval: the Reporting Interval defines how often the UC100 transmits the channel data (1 to 1080 minutes, default 20 minutes) ^[2].
5. Done: the UC100 polls the register at the set cadence and sends the active power via a LoRaWAN uplink to the gateway, network server and dashboard.

The same pattern applies to other values: on the SDM630, voltage L1 sits at 0x0000 (30001) and imported active energy at 0x0048 (30073) ^[10]. Instead of a meter, you can connect a PLC, a variable frequency drive or any other sensor with a Modbus RTU interface the same way.

From device to cloud: the architecture

The UC100 is one building block in an end-to-end chain. The typical path looks like this:

Modbus device → UC100 → LoRaWAN gateway → LoRaWAN Network Server → dashboard.

The gateway receives the radio packets and forwards them to a LoRaWAN Network Server. The open-source ChirpStack is a natural fit here: it fills exactly this role and forwards data over MQTT or HTTP to applications such as ThingsBoard, Grafana or Node-RED ^[6]. Which platform makes sense for analysis depends on the use case. Our comparison of ThingsBoard vs. Grafana helps with the decision.

merkaio offers exactly this stack as a European-hosted, sovereign platform, from the LoRaWAN connection via ChirpStack to the managed platform. That keeps configuration, data and cost in your hands.

What the UC100 makes possible

The real value of the UC100 is in the use cases it unlocks without new cabling:

• Energy sub-metering: read existing Modbus electricity meters per machine, line or building section to make consumption transparent, a typical basis for energy management to ISO 50001.
• Machine and production monitoring: capture registers from PLCs or drives, such as operating hours, states or counters, for analysis and predictive maintenance.
• Building services: connect HVAC, refrigeration or heating controllers into a unified monitoring view.
• Water and pumps: capture flow and level values from distributed, often hard-to-wire sites.
• Reading without cables: connect devices in places where new data lines simply are not worth it.

Why LoRaWAN makes this possible: it transmits in license-free ISM spectrum over long distances, penetrates buildings and needs very little power ^[7]. Instead of trenching or running Ethernet, a gateway within range is enough. For the background on building and operating such a setup, see our post on the IoT platform trap.

Honest limits

LoRaWAN is no cure-all, and that belongs in the planning. In Europe the 868 MHz band has a duty-cycle limit of around 1 percent on the main channels, in practice only a few seconds of airtime per hour ^[8]. Data rates are low, payloads are small, and sensible transmission intervals sit in the minute-to-hour range ^[9].

The consequence: the UC100 is built for periodic monitoring, not for millisecond control loops or real-time actuator control ^[9]. Anyone who needs to control a machine in a safety-relevant way still needs local control. Anyone who wants to collect, analyse and alarm on readings is in the right place with the UC100.

Context: alternatives and scope

The UC100 is not the only device of its kind. Comparable Modbus-to-LoRaWAN converters include the Dragino RS485-LN and RS485-BL or the Adeunis Modbus interface. For applications with additional inputs and outputs, Milesight itself offers the larger UC300. Which device fits depends on the number of registers, power supply and ingress protection.

If Modbus connectivity is only part of a larger setup and you want connectivity, data storage and dashboards bundled in one device, take a look at our own appliance, the merkaio edge pro.

merkaio: retrofit from a single source

Buying a single converter is quick. The effort is in the clean chain: choosing the right device, mapping the registers correctly, placing a gateway, operating the network server and reliably getting the data into a dashboard.

That is exactly merkaio's approach: IoT infrastructure from the sensor to the cloud, planned, installed and operated from a single source. If you want to connect existing Modbus equipment, let us talk about your use case. Discuss your project.

Sources

• [1] Milesight UC100 datasheet (PDF)
• [2] Milesight UC100 user guide (PDF)
• [3] Milesight UC100 product page
• [4] Modbus Organization, Introduction to Modbus
• [5] Modbus, technical overview (Wikipedia)
• [6] ChirpStack, LoRaWAN Network Server, documentation
• [7] The Things Network, What is LoRaWAN
• [8] The Things Network, Duty Cycle (ETSI EN 300 220)
• [9] The Things Network, LoRaWAN Limitations
• [10] Eastron SDM630 Modbus Protocol (PDF)