OpenMV H7 R2 powering from VIN but using USB

Hi all,

I’ve got an OpenMV H7 R2 that I want to power from VIN but still be able to connect to it using USB. When I cut the power pin of the USB though, I can’t connect to it even if the camera is powered using VIN. Why is this? Is there a workaround?


Why you need to cut this pin? it simply works without cutting it!

I’m cutting power to it, not cutting the pin itself. I don’t want to power it from the USB, that’s why.

how you supposed to connect with it if no usb cable is attached? i am totally confused.
how you cutting this power and why you have to do this? do you want to use the wifi shield?

I apologise for confusing you. I will be connecting this to a RPi Zero via UART + USB. I use UART to control the camera from the Pi, and I want to use the USB connection to load the camera filesystem on the RPi. I can currently do all this, but as soon as I cut the USB power my Pi can no longer see the camera (the camera is still powered by VIN). It is as if the USB bus stops working if not powered by USB.
I hope this clears things up.

unforunately nope.
I cant understand how you cut this usb power.
ANd i cant understand how a usb to serial device can work without power.
I am sorry too…

This is a USB connector, by desoldering or covering up the VCC pin, the host (Pi) no longer provides power to the camera.

Then I use VIN to power the camera and UART3 on pins P4 + P5 to communicate between Pi ↔ Camera.
Both the Pi and the Camera are powered up, I never said it’s supposed to work without power.

p4 and p5 are physical pins of the camera . they arent supposed to be in the usb connector.
the usb cable in this setup is simply not needed.
you must connect the camera pins txd and rxd p4 and p5 to pi’s zero pins 8-10 accordingly.
You must share the ground of them too.

I never said P4 and P5 are in the USB connector. UART is not USB. They are two separate things. I use the UART to communicate, and the USB to load the camera filesystem on the Pi.

did you share common ground for both the boars then?

this is what your first post looks like…

openmv board has a usb to serial chip beside the connector as all the other boards on the planet that use usb to serial communication. this chip is powered via usb connector. If no power is attached to usb connector the usb to serial chip isnt power up so there is tottaly communication break down!

Okay, that’s the piece of information I didn’t know about. Can you point me to the chip on the schematic?

hi there,

i checked the schematic i found and it seems that the data pins goes directly to the proccesor.

as i can see here you dont have to cut any pins cause the q2 mosfet already do this for you…
so keep the setup as it is without cutting the pin.
just ensure that you dont cut the negative pin cause you have to share the grounds…

If VBUS is connected then I can’t turn the camera On/Off using VIN because VBUS will still provide power to the camera. I want to be able to toggle power to the camera (hence why I want to use VIN). Based on the schematic, I don’t see why disabling VBUS would cause a breakdown in communication as long as the camera is powered by VIN?

Hi, the USB logic in the STM32 chip sense VBUS to operate. However, it’s powered by the main 3.3V regulator.

So, it might work. Give it a try.

Hi, thanks for responding. That was my thinking as well, but as soon as VBUS is disconnected, the camera is no longer detected. Is the USB not initialised unless VBUS is detected?

I guess so, you could look at the STM32 reference manual. The chip does sense VBUS though and probably shuts down USB if it isn’t present.

It’s kinda part of the USB spec… a usb connection without power doesn’t exist.

Ok, thanks for the heads up. It’s unfortunate as I want to bypass the delay on power on by USB. I guess I can modify the firmware to decrease the bootloader delay?

Hi there! What is the final purpose?
If it is for power saving then you can set a sleep mode …