A standard telephone keypad, with four rows of three keys each. The top row consists of 1, 2, and 3, with keys continuing down in order until the last row, which is usually *, 0, and #. Such a keypad ...
* arduino-cli compile --fqbn arduino:mbed_opta:opta examples/opta_opcua_server -v --build-property compiler.cpp.extra_flags="-DUSE_MODBUS_SENSOR_MD02=1" -u -p /dev ...
return ""; // if not handeled above then let the HTTP server send the reply itself (server files stored in /var/www/html directory or send 404 reply) ...