How did I fry my Teensy 4.1?

F

finnbsch

Member
Hi,

I designed a very basic PCB to mount the Teensy 4.1 with a variety of sensors. With a first test run, with only some components in place, everything worked fine. Then, adding different components before trying again resulted in the Teensy being fried. First, here is a list of things that are in use, referenced in the schematic. Note that some components were not in use at this point, but I included them to avoid further fries. Components in place in the first run are marked by ++ and components in place in the second run, which fried the board are marked by --. The numbers corresponding to the labels on the schematic.

[1] NRF24L01+ RF Module with 5V breakout board. The breakout board allows to supply 5V to the RF Module but leaves the signal lines unchanged at 3.3V (measured it to make sure) as seen here AdapterBoard --
[2] Adafruit 74hc595 uni-directional level shifter ++ --
[3] Sparkfun Bi-Directional Logic Level-Shifter 3.3V <-> 5V ++ --
[4] GY neo6mv2 GPS Module (not used so far)
[5] BMX160 IMU (not used so far)
[6] HC SR 04 Ultrasonic sensor (not used so far)
[7] External Shifting Power Regulator LM2596s. Connected to a 3S LiPo and set to 4.992V --
[8] HAKRC 4 in 1 20A BLHeLi_S ESC. This ESC is supplied externally by the same battery as [7] though the teensy and the ESC only share GND and Signals ++

In short, in the first test run, Teensy got power by USB, ESC was supplied by battery and ESC signals connected to the Teensy. In the second run, the Teensy was supplied by the Shifting Regulator and connected to the RF Module. After the second run, the teensy 3.3V reads 0.02V, the resistance between GND and 3.3V is very low and the Teensy isn't responsive so I assume it is fried. There is no obvious short due to metal on the board.
Here is the schematic:
image.png-mh (1).jpg

I have 3 questions:
1. What could have caused my Teensy to die? Any obvious mistakes in the setup?
2. How to avoid 1
3. Concerning the components that were not in use so far: is there anything that risks frying my Teensy again?

Best regards
 
Last edited:
I cannot edit my post so I'll post a reply instead:
The USB Power and External power were never connected at the same time. That being said, the shifting voltage regulator was connected when powered through USB but it didn't have a battery attached to it.
 
Hopefully someone will see something obvious.

But if it were me, I would try to remove as much of the stuff as possible, and see if the teensy will startup using USB.
If it does, I would then try seeing if it will startup using your external power, as I know that some do not work well with T4.x
I have had good luck with ones from Pololu as well as Murata(SP). But failed to startup with an BEC from Castle Creations(https://smile.amazon.com/gp/product/B000MXAR12)
Which worked fine for T3.x as well as some other boards, but not T4... I believe it has something to do with the voltage ramps up.
 
I have disconnected the teensy from everything else and tried powering via a range of different USB cables and different PCs. No luck
 
Did you cut the VIN/VUSB connection on the bottom of the board? If so, did you jumper it back? I have a few teensy boards where I have split them this way, and if I try to plug one of these into some other board and nothing working, it sometimes takes me a bit to remember and then create a connection.

Would also double check that there are no obvious solder joints that are causing a short.
And I know you have done some of this, but check resistence from VIN to GND, VIN to 3.3v, 3.3v to GND. And if they look reasonably OK, would then try to power,
and check voltage at VIN and 3.3v, which I know you said was really low 0.02v or the like, but could not tell if that was while stuff still connected or not. If the voltages are reasonable, I would then try the
15 second or so reset of the teensy, does the flash LED come on at all... If so does it reflash OK and you get blinking...

How to avoid... When I am building my own boards, and I am not being lazy (too often I am) I will try to solder or connect up many of the things first, like VR, BEC, ... and not have a teensy installed (probably have socket).
First simple checks for no shorts between VIN, 3.3v and GND.

If that checks out, then plug in and turn on battery, and check things, like, is the voltage going to the VIN pin. Is anything going into any of the 3.3v pins? Do any of the GND pins have voltage on them? And then probe each of the IO pins to make sure that if they have a voltage on them, that is not > 3.3v... Like I did not make a mistake and put in PU resistor connected up to 5v. Or that the level converters are working properly and again not feeding the IO pins with 5v.

Hopefully someone else will see something obvious.
 
Hi,
Thanks for your reply.

I didn't cut that connection.

I measured the resistances and voltages with nothing connected to the teensy but USB. 5V seems fine, resistance from 5V to GND also, but from 3.3V to GND it's pretty much non existent and 3.3V gives very low voltage.

Thanks for the advice. Is there anything else? As you can see, I didn't include and protection circuits or capacitors, simply because that exceeds my knowledge.
 
You must log in or register to reply here.
Back
Top