Teensy 4.1 Red light flickering

[MINJU]

I am trying to use a Teensy 4.1 board by connecting it to an external PCB. I cut the original power connection from the underside and am now supplying 5V power from the PCB. To do this, I cut a USB C to USB A cable and used only the +5V and GND lines, leaving out the ‘data +’ and ‘data –’ lines.

When I power on the PCB in this setup, the Teensy continuously blinks with a red light and does not operate properly. However, if I briefly connect the Teensy to my laptop through its micro USB port and then disconnect it, the board starts functioning normally again. (Didn’t need to do anything on my laptop just connected it and disconnected it after few seconds)

In this case, I would like to know whether the issue is with the Teensy board itself, or if it may be related to the power supply, PCB, or code.

 

[thebigg]

Check the code that is running on the teensy. The symptoms sound like the usual

while (!Serial) {

}

 

[PaulStoffregen]

When I power on the PCB in this setup, the Teensy continuously blinks with a red light and does not operate properly.

Slow steady blinking on the red LED (the one near the USB connector) means Teensy is running in bootloader mode where it expects your PC to connect to the USB port, but no USB communication has been heard.

Maybe the Program button is getting pressed? Or somehow you're causing the Program signal to be pulled low (same as pressing the pushbutton.

 

[MINJU]

Check the code that is running on the teensy. The symptoms sound like the usual

while (!Serial) {

}

THANK YOU SO MUCH YOU ARE THE BEST

 

[MINJU]

Slow steady blinking on the red LED (the one near the USB connector) means Teensy is running in bootloader mode where it expects your PC to connect to the USB port, but no USB communication has been heard.

Maybe the Program button is getting pressed? Or somehow you're causing the Program signal to be pulled low (same as pressing the pushbutton.

Thank you!!!!!!! I figured now

 

[PaulStoffregen]

Did you learn the actual cause of this problem?

Sharing this info might help other people who later find this conversation by search. Followup info about the actual cause of specific problems also helps us to answer questions better on this forum.

 

[MINJU]

Did you learn the actual cause of this problem?

Sharing this info might help other people who later find this conversation by search. Followup info about the actual cause of specific problems also helps us to answer questions better on this forum.

Oh yes. It was the problem that I had the “while(!Serial)” loop in ‘void setup()’ that made the system waits until the Serial is available. But since my pcb was not connected to computer, Teensy4.1 was not working.

So I deleted the while loop as you guys told me to and it’s now working well!!

Thank you so much for your help

 

[KurtE]

So I deleted the while loop as you guys told me to and it’s now working well!!

Note: Another option would be to add a timeout to waiting for Serial. I often do that, as it allows me the flexibility to
have it wait some at the start for me to connect up the Serial terminal, but it also then allows me to run it without USB.

Something like:

while (!Serial && millis() < 5000) {}

Note: this timeout assumes you are doing it at the start of a sketch, as millis() starts at 0...

But if you are doing it at some later point and wish to use a timeout then, you can do it a few different ways.

Something like:

elapsedMillis em;
while (!Serial && em < 5000) {};