Weird teensy + seeedstudio gprs module external power problem


So I have a teensy 2++ connected to seeedstudio sim900 gprs shield, when I connect the teensy to the computer via usb everything works perfect.

when I connect it to the computer with a usb cable which V+ is cut off and external power (12v battery through 5v regulator) it works perfect

when I disconnect the usb cable it stops working good and every few seconds I get normal power down.

Does anyone have any idea why?


Does anyone have any idea why?

Does anyone but you have any idea what code you are running?

I dont see how this have anything to do with the code

I run the same code, once with the computer plugged in and once without it.

I would guess that having the usb inside caused interrupts that got the arduino out of sleep mode.

does that sound plausible?

Its plausible if you enabled whatever interrupt you think is occurring.

You'd be better off asking about Teensy in the Teensy forums: PJRC (Teensy) Forum