I've noticed that when I'm sending serial data to my computer's serial monitor, the tx light only lights up when the serial monitor is open. When I close the monitor, it seems to stop sending data. Is this a normal thing?

The reason I ask is because I'm really trying to send data from my esplora to an uno, and I notice that despite (1) having the grounds of both arduinos connected and (2) connecting the esplora's tx pin (reset_lcd) to the uno's rx pin (pin 0) and the esplora's rx pin (dc_lcd) to the uno's tx pin (pin 1), the tx light on the esplora and the rx pin on the uno don't light up at all.

What could be the problem?

  • have you looked at the schematic of the Esplora board? .... What could be the problem? .... why do you think that there is a problem? .... you also said nothing about the actual data transfer between the Esplora and the Uno
    – jsotola
    Commented Oct 5, 2018 at 3:53
  • I’m sending integers as characters from the esplora to the uno and trying to read them as integers on the uno.
    – Paul
    Commented Oct 5, 2018 at 4:14
  • that says what you are doing ..... it does not say what happens .... you really need to clarify what is happening
    – jsotola
    Commented Oct 5, 2018 at 4:17
  • @jsotola: nothing happens. The tx/rx pins don’t light up at all, indicating that no data is being transfered. I can’t figure it out because i can’t communicate from the uno to the serial monitor while wiring the tx & rx pins.
    – Paul
    Commented Oct 5, 2018 at 4:28

1 Answer 1


Esplora is based on a MCU with native USB. The native USB reports connected only when it really connects. You have in setup() a while loop until the USB Serial is valid. The skech waits there for connection. Comment out the while (Serial) loop.

The TX and RX LEDs of Esplora are connected to the native USB port Serial interface. They will not light for the Serial1 interface.

You should disconnect the Uno from computer to not disturb the Serial interface with USB connection. Or use SoftwareSerial to communicate with Esplora and have debug prints to Serial Monitor.

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