Adding a modbus sensor is pretty easy.
Follow developer guide in this section, copy eg sdm120.json to be your template (https://raw.githubusercontent.com/boneIO-eu/app_black/dev/boneio/sensor/modbus/sdm120.json)
- model - model to show in Home Assistant.
- registers_base - array of registers. You can read multiple registers at once, it’s more CPU friendly.
- base - start index to read
- length - how many registers to read
- registers - array how to interpret data received from modbus device