ItsyBitsyM4 powered by power supply at VBAT pin

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gremlininusa
 
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ItsyBitsyM4 powered by power supply at VBAT pin

Post by gremlininusa »

Hi, I have the Itsybitsy M4 board connected to a LCD module. The LCD Vin pin is connected to 3.3V pin. It was working fine showing an image on the screen when the board was connected to the PC through USB cable.

I tried to power the board from VBAT pin by connecting VBAT pin and GND to a bench power supply. I set the power supply output to 3.5V but nothing happened. The onboard LED lighted up but nothing on the LCD screen. Then I increased the voltage to 5V and still nothing. It worked only when I connected USB cable to my PC.

I used a charger USB cable (VBUS and GND only, NO D+ and D-) and connected the board to the PC. It did not work. So I am thinking is it possible that this board would not boot up without the D+ D- pins connected? It does not make sense since the board is claimed to be able to get power from battery in VBAT pin.

Maybe I should not use bench power supply, and replace it with a real Li-Poly battery. Start with USB cable to let the board boot and then unplug the USB cable. Is that how it is supposed to work?

Maybe I missed something. Any help is appreciated.

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blnkjns
 
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Re: ItsyBitsyM4 powered by power supply at VBAT pin

Post by blnkjns »

Your code does not hang waiting for the USB Serial port to come live?

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alpierce
 
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Re: ItsyBitsyM4 powered by power supply at VBAT pin

Post by alpierce »

The battery input is also a charge port for the battery. Connecting a power supply to it is not a good idea. Using the USB port is the best way to power the board, it does not require the data lines to power up, only to program. You do need to make sure, as blnkjns said, that your code isn’t waiting for a serial connection at startup.

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gremlininusa
 
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Re: ItsyBitsyM4 powered by power supply at VBAT pin

Post by gremlininusa »

I see. Good suggestions. I'll check my codes. Thanks

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Franklin97355
 
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Re: ItsyBitsyM4 powered by power supply at VBAT pin

Post by Franklin97355 »

You might want to look at the pinout on the tutorial https://learn.adafruit.com/introducing- ... m4#pinouts

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