Cause of capture noise (1): power supply

dvd_colorbar
My set up is shown below.
Two boards, which are considered identical, except that: board A is coming with camera_A hard-wired, I reworked board B to have a RCA connector.
DVD player is external powered, camera can use the external power supply (camera_B), or battery inside(camera_C), or get the power from the board (camera_A).
There is no noise pattern seen with camera_A + board_A. However, when connecting board_B to
  •  DVD player, there are noise patterns captured. The fact is,
    • The DVD player works well with most boards, even the ones with the same decoder as board B.
    • Switch to another DVD player, the noise pattern is still there.
    • I did have some experience that increasing drive strength of the decoder avoided the noise patterns, on an old board. However, I have no idea how to avoid it on this board.
  • Camera B, noise pattern is seen, and even worse than DVD player: the pattern keeps moving vertically, and the capture module lost sync with the decoder frequently (when the noise pattern moves to the vsync interval, I guess).
I need eliminate the noise patterns of camera, to have some fair comparisons between camera A and camera B.
What I did:
  1. As the cable between cameras and decoder was re-worked by myself, I thought I brought some noises in while just twisting the wires together.
    • However, even I soldered the wires tightly, and made sure they were not exposed in the air (someone told me the wire would act as antenna if exposed in the air, and receive some noise signals, consequently), the noise pattern is still there.
    • Moreover, Camera_C doesn’t have noise pattern, even it is connected via the same wires.
  2. As camera_C doesn’t have this issue, we started looking into the power supply. A few options available:
    • Use the power from the board (not done,due to insufficient knowledge of the wire definitions on that board).
    • Use an alternate power supply, what we tried:
      • A 7.5V power supply with the same DC connector type (the noise is even worse, 3,4 stripes).
      • Rework the power cable to get power from laptop, via USB (failed, as USB can provide 5V maximum, but this camera requires a higher voltage (12V)).
      • Find a stable power supply.
        • Luckily, get one stable power supply. The connectors of this power supply is MOLEX connector. Therefore, cut and twist the wires of MOLEX connector with the camera power cable… and finally the noise pattern disappeared!!!!
Fundamentals:
  • DC connectors: Coaxial connector; Molex connector (4 pins, used for disk driver connectors).
  • USB connector pinout: Red is for VCC, black is for ground. White and green are for data.
  • Molex connector Pinout: yellow wire: 12V; red wire: 5V, black wires: ground.
https://i0.wp.com/www.shopaddonics.com/mmSHOPADDONICS/Images/AA4PFFPCBL.jpg
Update: there is one more cause which is worth to check: clock jitter resulted by wrong circuit design on the receiver side.
the two reasons above (low drive strength, or power supply) doesn’t introduce noise pattern if it is in Free run mode. If we do see noise even in free-run mode, check the circuit design.
See the image below. Removing R12102 and IC12102, and install R12100, will avoid the green line noise.
Screen shot 2015-07-10 at 11.02.35 AM
the IC is a bilateral switch, which makes the circuit tolerant of slower input rise and fall times when OE is low.
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s