Power with Teensey 4.1, Raspberry Pi, USB, and DEBUG

C

c172jeff

Well-known member
Hello,
I made a circuit board that houses both a Teensey 4.1 and Raspberry Pi. The board also has power inputs for 5V and Ground. When I power up the circuit board, both devices switch on and work correctly. They should be able to talk to one another. I have set the Raspberry Pi set to communicate via serial to the Teensey 4.1. I wish to power the circuit board via my external power supply AND (at the same time) connect a USB cable to the Teensey 4.1. This way, I can download programs to the Teensey 4.1 (for testing) and then soon after open a terminal program on the Raspberri pi to communicate with the Teensey (send a command).

I will make sure that the Raspberry Pi does not have the serial port open for when I am programming the Teensey/using the USB cable.

My question is this.... will the USB connection cause the smoke to come out of anything when the board is powered externally? Is there a diode that not cause my connected PC to be back fed with power from my external power supply?

On the circuit board, the 5Volt line from the Teensey is also connected to the Raspberry Pi (as well as my power supply).

Please advise,
Jeff
 
c172jeff said:
My question is this.... will the USB connection cause the smoke to come out of anything when the board is powered externally? Is there a diode that not cause my connected PC to be back fed with power from my external power supply?
Click to expand...
There are two pads with a connection between them that you should cut if you're going to power the Teensy externally and use the USB connection at the same time. You can see it in this picture:
teensy41_card11b_rev4.png

In the bottom right picture (labelled USB Device) which is on the bottom of the board, the two pads at the top. Don't cut too deep as the board has multiple layers. If at some point you wanted to power the Teensy from USB again, you can add a diode between the separated pads.
 
If you break the connection and then put a Schottky diode across them you get the best of both worlds without having to re-solder.
 
Thank you. I found out that the Teensey, when powered by USB, puts enough current on the 5v rail to power my Raspberry Pi additionally. So, I guess I can work using the do nothing solution. I did however look at the pad too see what I could cut to power this setup externally and I did not see evidence of a connection that needed cutting to do so. The trace must be very fine between those referenced pads requiring a very small new xacto point. I skipped it, but had thought the trace would have been larger and more obvious. I could not even see it.
 
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