Isolating the Teensy 4.1 from USB Voltage

Phil Barrett
4 days ago
2 min read

The Teensy 4.1 is an amazing product not only does it provide incredible compute power in a tiny package but it also is able to supply a good amount of 5V and 3.3V power for numerous peripherals. The T451U5XBB can run a complete CNC machine electronics with just USB power. However, sometimes you need more 5V power than USB can provide. The solution, of course, is an external 5V power supply unit. But, in that case, you will need to avoid joining the external PSU to the USB supply provide by your computer. Bad things could ensue. So, here are ways to avoid the problem

Block Power from the USB cable

Data only cables are available from lots of places but we recommend using a USB power blocker. A data only cable is hard to distinguish from a charging cable so it can cause confusion. Here's one example from Amazon.

Plug the USB cable into it and then plug it into the USB port on the computer. It will only pass data. Just make sure that you only use a cable with the power blocker attached. You can now fully power your T41U5XBB and Teensy 4.1 from an external 5V PSU.

Isolate the Teensy from USB power

This is a safer solution. It becomes impossible to accidentally plug the wrong USB cable into the Teensy 4.1. It involves cutting a trace on the bottom of the Teensy.

Photo courtesy of Ken Hahn, https://protosupplies.com/

Use a sharp knife and carefully cut between the two large(ish) rectangular pads on the bottom of the Teensy. Cut away from the Teensy in case you slip to avoid damaging other parts of the board. Use a DMM to verify there is no continuity between the pads. You can now fully power your T41U5XBB and Teensy 4.1 from an external 5V PSU. Use any USB cable (that fits).

You can convert the Teensy 4.1 back to using USB power by using solder to bridge the two rectangular pads. It may take more heating than you are used to and a little extra flux will help.

About Me.

I'm Phil Barrett, a long time CNC enthusiast. I run a small company, Brookwood Design, that makes several breakout boards for grblHAL and love to help people get the most out of their CNC machines.