MiSTer FPGA Forum

Hi there,
I was looking at getting a lag meter for my setup to check the video lag over multiple resolutions.
Now it looks like these devices only seem to support a handful of resolutions and need to be re-programmed when you want to change them.

This got me thinking, the mister I/O board has some spare gpio on that usb3 style connector.
1st,
Would it be possible to connect a photo diode to one of those pins?

2nd
We need something to read from on the screen that appears in all cores (to point the diode at). All core use the on screen display for configuration and setting. On the information screen could we have a small flashing white box. Next to it a simple readout that shows the time in MS measured from the diode.
This could be common across all cores and run at the resolutions set by the core.

What do you think? And could it be done?

Thanks for reading. Cheers

I have made some experiments with that idea

https://misterfpga.org/viewtopic.php?f=33&t=80
https://www.atari-forum.com/viewtopic.php?f=117&t=38261
http://temlib.org/pub/mister/latest.jpg

I've made various attempts for finding a suitable sensor, for example a PIN photodiode, a darlington-phototransistor,... but don't have yet a good solution. There are also several "light pen" schematics that may be useable.

Light intensity of displays vary a lot, as ambiant light, and sensor (phototransistor, ...) must be amplified for fast detection.

Maybe you can get some inspiration from the OSSC latency tester.
http://junkerhq.net/xrgb/index.php?titl ... ncy_tester

Thank you very much.
I will take a look at the electronics and use a multi turn pot to adjust the threshold levels.

I think the hard part is making part of the GUI flash with values displayed.
Is the GUI common or does it change from core to core?

One final thing, is there a pin out for the usb I/O connector?

Thanks again.

I've tried this OSRAM SFH300 phototransistor. Time Sleuth uses 300k resistor.
Due to the very high resistor, rise/fall times are quite slow. It's a bit faster with another NPN transistor as a Darlington.

The GUI with blinking rectangles was added to an existing core, keeping original resolution.
https://github.com/Grabulosaure/Genesis_MiSTer_latency