Fast Start OpenMV Script (with SD Card if applicable)

Hi Everyone,

I am using OpenMV H7 Plus. I am using 3.3V for the OpenMV to run saved script in SD Card. But everytime its loading like I plugged it with USB. (Green Led light blinking,then script starts). I saw a ticket about that and it says
“Hi, um, the bootloader is the thing that takes time. If you remove USB 5V and just use the VIN the bootloader is bypassed. Then it startups instantly.”

Can 3.3V VCC pin apply the same logic? If so why might it work this way? or is there any relationship with usage of SD Card?

Thank you in advence,


Yeah, it’s the same. Just don’t have USB plugged in. The MCU can sense the 5V on the USB bus and adjusts its behavior if that’s present.

Hi kwagyeman,

First of all thank you for your quick answer. I am not plugging in any usb in the OpenMV. But I am using all the pins through P0 to P12. Is there any way that it can trigger the USB Bus?

Thank you,

Screenshot from 2023-07-27 08-08-22

They should not.

Are you saying you are being hit with the 5 second bootloader timeout even with applying power via 3.3V?

Hi again,
Yes that’s exactly what we are experiencing right now.

Let me check that this happens for me.

Yeah, I see the issue. It’s boots immediately from VIN if I power via that, either 5V or 3.3V. But, if I power from 3.3V the bootloader runs with a timeout.

I see the reason why this happens. When you power via 3.3V the voltage goes backwards through the regulators and actually onto VBUS which makes the MCU think it’s plugged into USB. So, you need to power the system via VIN. 3.3V is not really an input.

The system functions fine using 3.3V on VIN.


Hi again,

Thank you for your effort. I will try it right now and share the results.

Thanks to the use of an ideal diode with reverse current blocking this cannot happen on the OpenMV Cam RT which will come out soon.