Teensy 3.2 externally powered is not starting

H

hellmut

New member
Hi everyone,

for the start, I've searched the forum (and other forums) but haven't found the answer.

The problem: Teensy 3.2 is running normally with USB power supply - from PC or power bank - when I'm connecting VIN and VUSB (as expected) (I have cut the pads for separating VIN and VUSB as explained in tutorial but can reconnect them with soldered pins). But it is not working when I try to power it from 5V regulator. I'm running Blink example (Arduino IDE 1.8.15) for testing.

With external power (VIN and VUSB disconnected):
- The orange led is on - little dimmed, not blinking.
- I can measure 5V between VIN and GND pins.
- I can measure 3.3V between 3.3 and GND pins.
- When switching power on without USB plugged - not working.
- In this "powered but not booted" situation, when I shorten 5V and GND for a moment Teensy somehow "resets" and starts to blink!
- When switching power on with USB plugged - not working.
- But when I then reload the program from Arduino IDE (It asks to press the button at first but works on the second attempt) - it starts to work again!

Does any one have a clue what is happening?
Thanks in advance!
Hellmut
 
Often times, you run into something like code that waits for Serial port.

while(!Serial) ;

Which works when you hook up, but not by external.

Most of my programs like this, put timeout in it. if (!Serial & millis() < 4000) ; // only wait up to 4 seconds
 
Do you have more than 1 Teensy board? Does the problem happen the same way on every board? (likely something wrong with the code) Or is this an issue happening on only a single board? (maybe a strange hardware failure or issue with 1 particular board)
 
This is probably not relevant, but sometimes we've seen cases were cutting the VIN-VUSB pads can sever a trace on the layer below inside the PCB. Details on this old thread:

https://forum.pjrc.com/threads/65611?p=264557&viewfull=1#post264557

Normally this would cause the board to not power on at all, which doesn't really fit the observations you've said. Still, you mentioned cutting the pads apart and this fits a general "strange power problem" description, so maybe this info might be worth a look.
 
@hellmut @Paul - VR Power supply issue? I have not seen it with T3.2, but with T4.x would not work with some power supplies. Something about too slow of ramp up time?
For example, several years ago (8-10) I was using one of these: https://smile.amazon.com/gp/product/B000MXAR12 (Battery Elimination Circuit) with a Teensy 3.2 and probably 3.6 (And RPI, ...), but
a Teensy 4 would not start up on it. That is if I turned on the switch which supplied voltage to it from a Lipo battery, the Teensy would not start. However if I then restarted the teensy it would run.
 
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