Tag: max4313

Genlocked

After resolving some DMA issues I now have a working testbed running on the STM32F413 mcu. It is using the signals from the timing board to drive an AD724. It is generating a good test pattern but connections are very finicky, since I have the AD724 on a breadboard. Noise is visible and jiggling the wires is sometimes necessary to get it to work. But it will do for the time being.

Rainbow test pattern, genlocked to incoming video
Scope trace. Horizontal sync is the short low pulse and the colourburst is the short sinewave following that.

In theory the output from this should be in phase with the video from my Runcam. To see if that is the case or not I need to have a working pixel switch. When I attempted to use the MAX4313 I didn’t see a picture, and when i checked the output with the scope I saw that the sync tips are being clipped off. It is attenuating the waveform when it drops below 0 volts. I will try clamping the sync tips to 1 volt to see whether it will pass the entire waveform through.

New Board Designs

New design is a timing board, which extracts all the signals needed for genlock but does not generate any video. There will also be a fast video switch on a separate board using a MAX4313 which is both a buffer and a switch. Switching time is around 40ns, much slower than the TI switch I was planning to use. But this may still be OK and does not require a negative supply. I will still make the negative supply board though and if the MAX4313 is not suitable I can make another board with the TI switch.

This is a modular approach. I intend to try generating the CVBS from the uC, but if this does not work out I can make another board with an AD724 as originally planned.

Circuit schematics are complete, currently working on the routing.

Assuming 52uS of analog video, 320*240 resolution means each pixel lasts 162.5nS. This means the MAX4313 which takes 40nS to switch, will take around 1/4 of a pixel when switching.

Video timing board design is uploaded to Github:

https://github.com/Batperson/video_timing_board