Modbus client to HTTP

[guczo]

I’m reading sensor data via RS485 with a TRB256 gateway via Modbus Serial Client. I need to send these to an HTTP API server in JSON.

The wiki documentation is not quite clear (to me at least) - tried several variations of custom JSON and LUA scripts but without much success.

How to pass variables to the JSON output from the Modbus serial client? I tried custom JSON templates with %% variables but nothing seems to work.

[anon65719490]

Hello,

Could you clarify what variables you are referring to? Could you also share screenshots of the custom templates you have already tried?

---

In the meantime, here’s a Lua script example that might be useful and demonstrates how to format Modbus responses into JSON:

-- Available variables:
-- data_sender.section - config section name
-- data_sender.version - LUA plugin version
-- env - data to be formatted
--
-- String value must be returned

local json = require("luci.jsonc")

function handle_format_request(data)
    local result = {}

    result.meterID = data[1]["server_name"]
    result.values = {}

    for _, modbus_response in pairs(data) do
        table.insert(result.values, {
            modbus_response["date"],
            tonumber(modbus_response["data"]),
        })
    end

    return json.stringify(result)
end

This script will produce output similar to:

[
  {
    "values": [
      ["11/10/2024 08:56:27", 6505],
      ["11/10/2024 08:56:27", 6505]
    ],
    "meterID": "data"
  }
]

Best regards,