Flow returns blank line between readings

[E1cid]

You will find a solution here

Remove manuel line break from string for msg.payload and switch

You can use a function node to trim the payload before the switch msg.payload = msg.payload.trim(); return msg; or use JSONata in the switch property $trim($$.payload) [Screenshot_20220405-160340]

Or
you could change the output of the Arduino code to
Serial.println("{\"T1\": " + (String)temp1 + "}"); to output an json string.