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My serial monitor keep showing these unreadable characters. Anyone know what is going on? Many thanks!

Schematic Physical Physical2

  • maybe the data is binary, not ascii
    – jsotola
    Apr 2, 2018 at 18:59
  • Can you try a minimal example of Serial.begin(9600); Serial.println("Hello world!");? Apr 2, 2018 at 19:14
  • @MaximilianGerhardt Hi yes one line of hello world appeared
    – Parto
    Apr 2, 2018 at 19:19
  • Then start adding connections, components and code until the error shows up. Does connecting RX to the Arduino change anything? Apr 2, 2018 at 19:20
  • @MaximilianGerhardt Yes connecting to RX looks normal but after connected ground to ground unreadable codes appear
    – Parto
    Apr 2, 2018 at 19:23

1 Answer 1


It can have many reasons, but the most likely are:

  • You set the baudrate wrong
  • You set the stop/start bits wrong
  • You send wrong data
  • The cable is bad

It helps if you show your sketch(es), for sender/receiver and possibly your circuit.

  • 1
    Hi Michel thanks for your suggestions, these are my sketches and circuit: imgur.com/a/Ksg4w
    – Parto
    Apr 2, 2018 at 19:06
  • It seems the baudrate is correct, start/stop bits is hard to see. Probably the date you send is wrong, you should check what happens in the Brains functions you call and what is returned (which is what you send). Apr 2, 2018 at 19:12

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