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Debugging
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Medion MD-85572 case is tear-shaped and mounted on flexible arm. The photo below shows the camera.
To open the camera you need to unscrew three small screws holding both parts of the case together. Then it should be possible to remove the top part along with the camera pcb.
 Bottom view of the opened camera |
 Back view of the opened camera |
The camera board with the lens holder and outer black plastic ring is held by the two plastic bolts protruding from the top case part. It should be possible to separate the black ring from the case and get it out along with the pcb without using any excessive force. Just watch out for the shutter button, as it's melted to the case and may be easily broken. Next step is to remove the outer plastic ring secured to the camera PCB by two screws.
All that is left is to remove the camera lens holder, it's held by two screws from the back of the board. At the end you should have the full access to the board, including the camera sensor area. The following photos show the camera PCB waiting to be modified.
 Back side of the PCB |
 Front side of the PCB |
This camera is a bit harder to modify than WB-5400 - the whole board and the sensor chip package is much smaller, traces are short and narrow. I soldered a thin wire to pin 14 in the first camera to get access to FSIN input and to pin 41 in the second one to get VSYNC output signal. Soldering to pin 41 was a real challenge, as there's a resistor on the board very close to it. The following photos show the wires soldered to the pins.
 Connection to pin 14 (FSIN) |
 Connection to pin 41 (VSYNC) |
In this case it was not necessary to cut holes in the lens holder to get the wires out as it's mounted about 1 millimeter above the board. The picture below shows both cameras modified and ready for experiments.
In order to check the synchronization of the webcams I carried out two experiments.
The first experiment was to record video stream simultaneously from unsynchronized cameras pointed to the timer working with sub-second resolution and check if asynchronous operation of cameras can be confirmed by comparing the frames from both streams. I recorded 100 frames of video stream from webcams pointed to the computer monitor with the timer application running on the screen. To get the video stream frames I used video capture utility from Video4Linux 2 API website. Both webcams were running in 1280x1024 resolution with 15 fps.
This image shows consecutive recorded timer values from both cameras. The top sequence is from the first camera, the bottom is from the second. It's easy to see that they are running about 4-6 milliseconds out of sync. Consider for example the part below:
In the next experiment I connected VSYNC output of the first camera to FSIN of the second and recorded video stream simultaneously from both cameras. Again they were pointed to the same timer application window visible on the computer monitor and 100 video frames were captures from both cameras in order to compare the recorded time values. This image shows consecutive recorded timer values from both cameras. As you can see, recorded time values are pretty much identical. Take a look at the part of the sequence below:
As far as I can tell from the visual inspection of both sequences, cameras were running synchronously.
From the conducted experiments it's safe to assume that connecting VSYNC output of the first camera sensor to FSIN input of the second camera sensor resulted in both webcams running synchronously.
Medion MD-85572 has been identified as another cheap consumer-level webcam capable of receiving an external synchronization signal, suitable for amateur computer vision experiments.
