Teensy 4.1 does not boot via VIN-Pin


New member
im fairly new to the Teensy-Community and got a (at least for me) big project around. Im want to design a PCB to drive 4 stepper-motor-drivers (TMC5160 pro) with some accessoires (display, endstops, rotary encoder).

I cut the trace on my teensy between vusb and vin and soldered a shottky diode between. Later it should only be powered by the L78S05CV 5V of my PCB. While coding, i recognized the teensy does not power on with only 5V at VIN Pin applied. (But it starts flashing red, when i press the program button).
If i plug in my USB (while 5V at VIN) and reset, it powers on like normal. So the teensy needs the USB to boot - after booting i can unplug the USB and it keeps on running properly

Is there anything wrong with my scematic? (sorry for the kinda wild wiring). The code should not be an issue - same problem with the Blink example.

The big red pads are jumpers. I also got an external 3.3V power source, to run the peripherals. It can be connected via Jumper to the Teensy (but is not used).

Thanks for your help.
Kind Regards


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Do you have something like this while (!Serial); in your code (in setup)?
If you do, when the USB is NOT plugged in, it will wait there forever, waiting for the USB to appear.
If that is the case change your setup code to something like below:
void setup() {
    while (!Serial && (millis() < 3000));
This code will wait for up to 3 seconds for the USB to appear, and then continue.
Well, i guess thats it - what a rookie mistake. Indeed i got
while (!Serial);
in my setup.
You saved my day! Thanks!