Monitoring Serial (USB): TXD0/RXD0 on Grove connector nr3


because I want to monitor the serial output of my mbilly board (without causing a reset), I try to use the Grove connector nr 3 which are the same I/O lines that are connected to the USB port.
For security I didn’t connect the 5V line.
So I connected for grove nr 3
grove GND (black) => USB GND (black)
grove RX (white) => USB D- (white)
grove TX (yellow) => USB D+(green
grove +5V (red) left free => USB +5V (red) left free

I also swapped the RX and TX but no progress. I don’t see the output
How can I monitor the USB port of the Mbilli ? Using Arduino Serial port monitor ? or Putty ?

Hi @JohanHydro,

USB or RX0/TX0 -> Serial.print
BEE or RX1/TX1 -> Serial1.print

When powering the board by USB you indeed don’t need to connect the grove vcc line.
The output voltage of the USB is 5V, the grove and bee header have a voltage of 3.3V.

Both Arduino IDE, Putty or any other Serial Monitor will work.
Did you connect the grove pins to an ftdi chip before connecting it to your pc?

Kind Regards,


My portable gives =
"The USB device on this pc malfunctions " I can not see it on the arduino serial monitor

there is indeed a GPS connected to the Grove 5 pin 18,19 and it is powered

What do you use to connect the grove pins to your pc?

A Grove connector on the Mbilli => cutted it in the middle => cutted a USB cable on my PC in the middle => connected the tree wires (5V not connected)

Is it maybe TTL serial output ? should I use a TTL/RS232 converter and monitor on my RS232 port of my PC ? Or is it USB directly compatible

You indeed need a TTL converter in between.

I thought so,
I’ll try and let you know

It works with the serial TTL to RS232 converter and hyperterminal

thanks !

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