Arduino Nano: RX & TX LED stuck on while charging via Vin Pin

Hi everyone!

I've got a problem with the onboard LEDs on my Arduino. I am using the Bluething Board, which is basically a Arduino Nano combined with a pre-installed HC-05 module. Here is a rough schematic of the Board:

I am using the Arduino as a Datalogger and I am powering it with a LiPo-battery via the Vin Pin. This works perfectly fine apart from the fact that the RX and TX LEDs (D3 and D4 in the schematic) are always on. Since no data is transmitted via the USB-connection they should be off. The LEDs D6 and D7 signal whether data is transmitted to or recieved from the HC-05 module and work as intended. Since I want to run the Arduino for as long as possible without charging I would like to turn the LEDs D3 and D4 off, but by now haven't found a solution how to do so.

While charging the Arduino via the USB-connection both LEDs only light up when transferring Data from the Computer to the Arduino or the other way round - just as intended.

If anyone has some ideas or a solution I'd be glad to hear them!

Have a nice day!

PS: If it is any help, here is my code (please don't judge my coding, still very new to Arduino-Community :confused: ):

#define rxPin 11
#define txPin 12
#define sensorPin 0
#include <SoftwareSerial.h>

SoftwareSerial HC05(txPin, rxPin);

void setup() { 
  Serial.begin(57600);
  HC05.begin(38400);

//some setup commands for the HC-05 module

  analogReference(DEFAULT);

void loop() {
  int sensorValue = 0;  
  byte highbyte, lowbyte, crc;
  sensorValue = analogRead(sensorPin);
 
  HC05.flush();
  highbyte=sensorValue/256;
  lowbyte=sensorValue%256;
  crc=170^highbyte^lowbyte;
  HC05.write(highbyte);
  HC05.write(lowbyte);  
  HC05.write(crc);

  delay(40);
}

So don't call Serial.begin(). The Serial pins will be left untouched as floating inputs and the LEDs will be off.

For the LEDs showing the comms with the bluetooth, you can unsolder them or it's usually easier to unsolder their associated resistors. If you don't have a soldering iron and you can't wait for your birthday to get one, then just destroy the LEDs with needle-nose pliers. Crush them, rip them off the board.

Thanks for your reply!

I just tried it, but unfortunately it makes no difference. I use the serial.begin so I can see if something is wrong with the setup of the HC-05 module. I deleted all lines in the code which used the serial interface including Serial.begin in the beginning. The program still works as it should but the LEDs are still on.

As for unsoldering the LEDs: While it might be an option, I find the LEDs for the bluetooth communication quite helpful, so I might just leave them on. The other two on the other hand do not have any benefit for me in this application so I might just unsolder these. Unless this causes any other problems with the board, I'm unaware of?

Still if anyone has a solution on how to get by with this problem without unsoldering the LEDs I would prefer that. Just for re-using the Arduino after I am finished with this project.

The CH340G controls the Rx pin no matter what you put in your program. I think your only choice is to desolder the LEDs. Hacking into that chip's power supply is more likely to brick your board.

pattex31:
I am powering it with a LiPo-battery via the Vin Pin.

I assume two Lipo cells in series (7.2volt).
Anything less than 6volt on V-in could do unexpected things.
Leo..

MorganS:
The CH340G controls the Rx pin no matter what you put in your program. I think your only choice is to desolder the LEDs. Hacking into that chip's power supply is more likely to brick your board.

Okay, that is a bit unfortunate but makes sense.

Wawa:
I assume two Lipo cells in series (7.2volt).
Anything less than 6volt on V-in could do unexpected things.
Leo..

Yes, that is exactly what I am doing. Sorry for not specifying.

What happens if you comment the USB serial line out.
// Serial.begin(57600);
You don't need it anyway.
Leo..

That's what MorganS first suggested. I tried it without any serial commands but it made no difference...
I'm using the serial interface for the setup process of the HC-05 module. Which it is not necessarily needed for, but nice to have for troubleshooting.

Sorry, missed that.
Leo..