FSYNC with pulldown

precira

Hi
I have an OAK-TOF camera with Fsync input (M8 connector).
According to https://docs.luxonis.com/hardware/platform/deploy/frame-sync/#Frame%20Synchronization-Hardware%20syncing-FSYNC%20signal-External%20FSYNC%20Example

there is a pullup resistor at this fsync input.
I want to trigger the camera in snapshot mode with a simple GPIO output. The way I see it, this pullup is very annoying for this scenario since I don't see a way around using an additional mosfet. Or is there?
However, it says 'by default'. How can I change this to pulldown?
With a pulldown it should be possible to simply use the GPIO directly.

jakaskerl

precira
Unfortunately the PU is on the PCB on both sides of the level shifter. Couldn't you just use inverse logic for the GPIO and achieve the same result?

Thanks,
Jaka

precira

Simply connecting the GND and a GPIO directly to the camera and using inverted logic does not work because the camera pulls its input high. If I put the GPIO to 0V this is not enough to stop the camera exposure. To stop it, I really need to shorten the input to ground. I solved this now by using a mosfet like so:

GPIO ------ mosfet gate ; Camera GND ----- mosfet source ---- GPIO GND ; mosfet drain --- camera trigger

if GPIO is HIGH, mosfet is conducting and shortens the cam trigger to ground. When I want to take a picture, I pull the gpio low for 1ms.

I think the trigger input would have to be floating for it to be possible to simply connect directly to the GPIO, which I guess would have downsides as well.