Teensy MicroMod Serial Monitor Disconnects After ~5 Seconds

Development Boards Teensy
1

Hi,

I’m using a custom Teensy MicroMod carrier, and my Serial Monitor disconnects about 5 seconds after starting. However, the main loop keeps running fine. I confirmed this because my LED blinking code continues working:

void setup() {
Serial.begin(9600);
while (!Serial) {;} // Wait for serial (optional)
delay(100);
Serial.println(“Serial test started…”);
pinMode(13, OUTPUT);
pinMode(9, OUTPUT);
}

void loop() {
Serial.println(millis());
Serial.flush();
digitalWrite(13, HIGH);
digitalWrite(9, LOW);
delay(100);
digitalWrite(13, LOW);
digitalWrite(9, HIGH);
delay(100);
}

Has anyone seen this issue before? Any ideas on what could be causing it?

Thanks!

2

I have just tried your sketch on my ATP carrier and Teensy. It works without a problem. I only needed to update the udev-folder on Ubuntu. Is your serial monitor set for 9600 ?

3

Thank you for the reply!

I’m using Arduino IDE to program on Windows 10, and yes, the Serial Monitor is set to 9600.

Everything works fine on SparkFun’s MicroMod ATP Carrier Board, but when I use my custom carrier board, the Serial Monitor only outputs for about 5000ms (~5 seconds) before the USB serial disconnects. I have to reconnect the USB to get the serial connection back.

Could this be due to my USB D- and D+ PCB traces being too small or too long?

Here’s my basic USB to Teensy MicroMod connection:

  • USB VIN → 5V
  • D+ → Teensy D+
  • D- → Teensy D-
  • GND → GND
  • 3.3V → 3.3V

Any thoughts on whether the PCB routing could be the issue? Thanks!

4

Can’t really help you on that, but looking at the schematics I would expect these are the right connections.

The USB / Serial on a Teensy is a bit special. There are many articles about that like Teensyduino: Using USB Serial with Teensy on the Arduino IDE

Maybe trying increase the delays in the loop()

5

Try making a shorter testing rig to see. Also, is your setup self-soldered? If so, maybe share a photo of the connections

6

Update: Problem Solved!

The issue was indeed with my PCB routing—the USB D+ and D- traces were too thin, which caused unstable USB communication.

I fixed it by paralleling D+ and D- with external jumper wires, and now the Serial Monitor works perfectly, even after long periods.

Thank you all for the responses and support! :folded_hands:

1 Like
7

Good work!