Teensy 4.0 VIN problem.

[philjynx]

When VIN-VUSB is cut to prevent backfeed of power to the PC the Teensy will not run.
When not cut, it still won't run on the VIN supply. It will, however, run on VUSB.
VIN (under load with the Teensy & a Raspberry PI connected) is a steady 4.93 volts provided by a switch mode on board supply.
VUSB (which also powers the RPI since they are on the same power rail on the PCB) is a steady 4.96 volts.

One more detail: If I power up my project (on its own 4.93 volt supply) and then very briefly connect the USB to the PC, the Teensy starts.

I've built essentially the same project previously with Teensy 3.2 and 3.5 using the same power supply and never had this problem.

Ideas?

 

[defragster]

One thing seems relevant : "One more detail: If I power up my project (on its own 4.93 volt supply) and then very briefly connect the USB to the PC,"

That sounds like the typical problem of in setup() is something like :: while (!Serial ) {}

With that the code the Teensy will sit forever until 'connect the USB to the PC'.

If present that code needs to be removed or altered to something like this for time controlled 4 second wait: while (!Serial && millis() < 4000 );

 

[philjynx]

One thing seems relevant : "One more detail: If I power up my project (on its own 4.93 volt supply) and then very briefly connect the USB to the PC,"

That sounds like the typical problem of in setup() is something like :: while (!Serial ) {}

With that the code the Teensy will sit forever until 'connect the USB to the PC'.

If present that code needs to be removed or altered to something like this for time controlled 4 second wait: while (!Serial && millis() < 4000 );

Ha! Thank you heaps! I did indeed have that "while forever" in my code. I only ever use serial for debugging, on this occassion that was the bug! I was on the verge of ordering another Teensy thinking I'd somehow broken this one.

 

[defragster]

quite welcome ... Always a bit nerve racking to cut that trace - then having it act differently causes wonder ...