24kHz noise from Teensey or PC / Power Test


Well-known member
In my project, I notice a 24kHz anomaly that happens only when the Teensey is powered by the USB on my computer.

I'd like to test my setup using a USB power supply (that can charge a phone), but sadly, my Teensey program does not start.

Why would this be so? When the board is plugged in via a wall wort, a dim red light starts blinking when I press the button, this is in contract to the bright orange led when its powered by the computer? Any ideas?

In my project, I am seeing a 24kHz signal that seems to be noise from the pc. My hope is that this disappears when powered by something cleaner, but I suppose it could also be from the Teensey 4.1 . 2 different Teensey 4.1 show the same 24kHz. But when powered by the PC.

Since I have an SPI bus, this noise might matter in my project. Would a certain sized Cap to ground on the power rail get rid of this noise?

Thanks for any help.
a dim red light starts blinking when I press the button

If you are referring to the button on the T4.1, that is the PROGRAM button. You would not normally be pressing that button and expecting anything (other than initiating a PROGRAM cycle, where the firmware is transferred from the PC to the T4.1) during normal operation.

More than likely, you will find that your sketch contains a line like this in the setup() function: while(!Serial)

This line tells your T4.1 to wait until the USB Serial interface is active. When you are running your T4.1 from the wall wart, the USB Serial interface is not connected to anything active (like a PC), so it will wait there forever... If your sketch includes this line, try commenting it out & see if that changes the behavior.

Mark J Culross
I am still trying to investigate that. It requires me to use external power and send commands from the Rasp Pi. Last time I checked, the Teensey does not want to talk/listen to tx and rx when i thought it should . Ill do more tests later to see it was setup right. Maybe even use a 24 volt battery to reallyt teh noise issue.