Edge Gateway

Modbus to SQL database

A Modbus device, written as rows into SQLite on the gateway or into PostgreSQL, MySQL / MariaDB or SQL Server.

The data flow

Every published value becomes a row: ts, device, tag, value, text_value, quality, unit, with an index on device, tag and time. Rows are inserted in transactions of Rows per transaction, collected for Batch wait milliseconds.

The rows, in PostgreSQL

ts                            | device     | tag        | value | quality | unit
2026-09-29 07:25:03.629+05:30 | Main meter | Voltage_L1 | 230.5 | GOOD    | V

In the editor

A rate limit keeps the table to one row per tag every ten seconds however fast the device is polled.

SQL out chooses the database. SQLite writes a file in the gateway's data directory and needs nothing else. PostgreSQL, MySQL / MariaDB and SQL Server take host, port (the engine's default when 0), database name, user name and an encryption setting. Create the table when it is missing is on by default; Delete rows older than keeps the table bounded.

The database password is never in the design. After the install, on the device: modbuslogic-edge secrets set <destination-id> password. The runtime keeps it encrypted there; a design or a download can be shared without carrying it. The destination id is in the log line the runtime prints for the destination, and in project.json under the data directory.

Test it with the Modbus Simulator

You do not need the PLC to try this flow. The Modbus Simulator answers as a Modbus slave on your own PC, with registers that move, so the whole path from polling to the output can be watched before any hardware is involved.

Start the Simulator and add a slave: Modbus TCP, bind host set to this PC's LAN address (the prefilled one), port 1502, unit ID 1. Add a few holding registers, say 40001–40010 as FLOAT32 or INT16 in random mode so the values change, and press Start.
In the editor, set the source node's host to that address, port 1502, unit ID 1, and the same addresses and data types. Poll interval 1s is fine.
Deploy the design to a device on the same network, or to this very PC: the Edge Gateway Console installs on a laptop as readily as on an edge computer, and the gateway polls the Simulator over the LAN.
The Simulator's request log shows the gateway's reads arriving: function code 03, the start address and quantity, once per poll interval. Neighbouring registers arrive as one read.
SQLite needs no server: leave the default and read the file with any SQLite tool after a minute of polling. For PostgreSQL, a local server and SELECT * FROM modbuslogic_values ORDER BY ts DESC LIMIT 20 shows the Simulator's values arriving as rows.

Registers in fixed mode make a deadband or a condition easy to exercise: change a value by hand and watch what is, and is not, published. A register set to a value the Simulator refuses (uncheck Fill unmapped and read an address that is not there) shows what a BAD quality looks like at the output. The Simulator's own page has the rest.

From design to device

Validate. On the design page, Run validation. The editor's rules, the tag document and the runtime binary itself check the design; every issue names its node. Details: Validating a design.
Install. From the Devices panel download the installer for the device's platform (Windows x64, Linux x64 or Linux ARM64). Windows: extract and run Edge-Gateway-Console.exe from an administrator terminal. Linux (Debian, Ubuntu, Raspberry Pi OS): sudo dpkg -i the .deb, then sudo edge-gateway-console. It shows the device code. Details: Installing on the device.
Device code. Enter it in the Devices panel, choose a trial or one of your purchased licences, and press Download activation bundle: one small zip with the design and a licence bound to that machine, sealed so only that machine can open it. Details: Downloading.
Bundle. Give the zip to the console (drag it onto the program, pass its path, or put it beside the program and run it again; a USB stick is fine for a device without internet). It opens the bundle with its own code, installs the runtime as a service and starts it. The device never contacts the site. Details: Activation and the licence.

The console then opens the gateway's web view in a browser (on a device without a desktop it prints the address instead) and stays attached with the live view: devices up or down, values as they change, what was published, and the log.

The live view shows the database as connected and counts rows sent; a wrong host or password appears as the last error.
The table fills at the rate the route allows; with a rate limit, one row per tag per interval.

Ctrl-C leaves the gateway running as a service. Run edge-gateway-console again at any time: it shows the service, the licence, every device and destination with what to check, the web view, and the live log. Running covers the data directory, secrets and the diagnostics.