Did cutting the VUSB / VIN Ruin my Teensy 3?

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mcsteeze

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Hi,

I am trying to use the OCTOWS2811 Library with my Teensy 3. I followed the directions, where it says to cut apart the two pads on the bottom. (This, by the way was more difficult than anticipated). However, now there seems to be a problem with my Teensy. No lights appear, and the serial port to which it is connected no longer appears in the Arduino IDE. This is true whether I attach the Teensy to USB alone or via a 9 volt batter or 5v power supply. Additionally I think something is wrong because when I connect it to a battery it drains the 9v pretty quickly. Is there anyway I can test that the Teensy is at least somewhat functional? Pressing reset does nothing and I can't even get it to blink. Has anyone heard of problems that come up when doing this?

Also, Any ideas on why the Teensy should "usually be powered by the same 5v power supply"? Thanks
 
Gosh darn it (I assume the same is true for a Teensy 3).
Well, to get some use out if this post, I understand that cutting the VUSB pad will make it so the Teensy draws power from the external source but why is this neccesary? For instance why is it reccomended to do this with the OCTO Library?
 
You can run the Teensy from either USB power, or the power supplies that power the LEDs. But not both, because that could allow the LED power to feed back into your computer. The VUSB-VIN jumper is meant to allow you to cut the connection, so VUSB doesn't try to power the board, which lets you power if from 5V power supplies without worry about that power feeding back into your computer.

These big LED projects vary quite a bit. For example, this one we built for Freescale a few months ago was totally stand-alone. It read the video and audio from a file on a SD card. There was no computer connected. In a case like that, you could leave the VUSB-VIN connected, if you never try to plug in the USB cable again after it's hooked up. Of course, that would suck, so for that project I cut them apart.

Many projects are based on the VideoDisplay example, where you always need a USB connection to feed video data to the Teensy. For those, you can leave VUSB-VIN connected. Or you can decide to power from the 5V for the LEDs. It's up to you. The VUSB-VIN jumper is meant to give you options.

However, the VIN pin is specified for 3.7 to 5.5V. If you apply more than 5.5 volts, you're risking damage to the Teensy. A 9 volt battery will certainly kill the Teensy, unless you use something like a 7805 voltage regulator to reduce it to 5V.

If the VUSB-VIN jumper is not cut, touching a 9V battery to VIN and GND while the USB is plugged in could also damage your computer! Be careful.
 
Thank you for the precise response. I understand it much better now. Also thanks for the great link to your display.
 
Personally rather than risk damaging my Teensy, I just cut the 5v line in a USB cable instead. In my cable this was red, but if you check the pinouts (http://en.wikipedia.org/wiki/USB) you can make sure you get the correct cable. This way you can easily swap between powering the Teensy & LEDs from an external power supply using the cut cable, or from the PC just by swapping cables over. Arduino's can be powered from an external 9v source which I imagine is why you tried it, but Teensy's need 5v as Paul put above.

I also accidentally found out you can power a surprisingly large number of LEDs (~100 @ 30% brightness) using just the usb power from a PC and not an external power source without melting the PC or the Teensy. I wouldn't recommend it though!
 
Personally rather than risk damaging my Teensy, I just cut the 5v line in a USB cable instead.

This is great, I don't know why I didn't respond earlier! You are right, I was used to using 9V on my UNO and then was dumb enough to try it on the Teensy.

What you are saying is that now you have two USB cables. One that you use with the teensy and and an external power source and one that you use when you need to power/reprogram the teensy? I like it.
 
This is great, I don't know why I didn't respond earlier! You are right, I was used to using 9V on my UNO and then was dumb enough to try it on the Teensy.

What you are saying is that now you have two USB cables. One that you use with the teensy and and an external power source and one that you use when you need to power/reprogram the teensy? I like it.

Almost. You can reprogramme the teensy using both. It just changes where power is taken from. For low power circuits (< 500ma) with a few LEDs it's fine to power them using a normal USB cable from the PC and no external power. For a larger number, you would damage the USB on the PC & Teensy, so use the cut cable and an external power supply. You can still programme the Teensy this way, but it doesn't draw power from the USB on the PC, and you can inject power into the cables directly from the external supply without it going through the Teensy.

Two cables means you can swap between situations, without needing to modify the teensy at all.
 
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