Interfacing with Linear CCDs

Discussion in 'General Electronics Chat' started by bxh, Dec 31, 2012.

  1. bxh

    Thread Starter New Member

    Dec 31, 2012
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    Hello all,

    I'm new to this forum, and decided to register after reading some interesting threads. I've experience in electronics and programming, having built several robots.

    I've been interested in upgrading my skills with sensors by learning how to interface with an image sensor. After quite a bit of searching, I decided it might be a good point to start with a Linear CCD. All I aim for (for now) is to be able to correctly make a single read. Speed is not important, though for this project, I'll probably choose to use an ARM Cortex-M4 MCU.

    I've found several linear CCD manufacturers, but haven't found suppliers. However, since there is a datasheet available for this CCD, I've been assuming I'll be using it.

    Based on the datasheet, it simply looks like the sensor wants a few additional components (as shown in the test load configuration) and a few clock signals (x, T and IC?). The data will then be pushed out at the two Vout pins to be converted using ADCs.

    This looks too straightforward to be true. There must be pitfalls just waiting for me.

    I've found several threads where people have talked about interfacing with linear CCDs, but there isn't a lot of information. There are some who posted about their success but without details.

    Before I take a leap into the deep water (buy the CCD), I'd like to hear about your experiences interfacing with CCDs, the problems they faced, common pitfalls, things to avoid etc. If someone has a schematic to share, it'll be very helpful!

    Thanks in advance.

    Hon
     
  2. davebee

    Well-Known Member

    Oct 22, 2008
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    I'm not an expert but I've used a few CCDs and linear light-sensitive diode arrays.

    The biggest problem I've had is getting uniform lighting on the object being detected.

    Lighting seems like it should be so easy, but in practice, I found it surprisingly difficult to avoid major peaks and valleys in the response from lighting irregularities.

    If you can take dark frames and flat field frames for post-processing the received image, you can clean up some lighting irregularity, but it's better to get as smooth lighting in the original image as you can.

    Edit - I don't think you should need to be concerned about the basic electrical operation. In my experience, if you follow the data sheet, the devices do just what they are supposed to.
     
    Last edited: Jan 2, 2013
  3. bxh

    Thread Starter New Member

    Dec 31, 2012
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    Thanks for replying. I'm not sure I understand the problem though. Could you give an example of this problem?

    Also, I've looked around more after I've started this thread, and I found more information. For one, I found relatively cheap linear CCDs that are sold on eBay. I've decided to buy one of the cheapest ones, the TCD1703C, which has quite a high pixel count.

    It's quite common for people to ask about driving the gates on the CCDs. The datasheet seems to imply that just 5V pulses are required, but is it that straightforward?

    The TCD1703C datasheet shows that there are 10 clock pins, some of which are Phase 1, some Phase 2 and there's a "Final Stage Clock". Nothing else is mentioned about them. Any ideas?
     
  4. davebee

    Well-Known Member

    Oct 22, 2008
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    well, suppose you want to make a line follower for your robot. You focus the image of a line onto your sensor and write a program to locate the line.

    But instead of a smooth bar where the line is like what your eye sees (and your brain interprets), the data from the sensor looks like a mountain range with multiple peaks and valleys and slopes; much harder for a program to make sense of. Good lighting will help make better incoming data.

    I don't know about that sensor. I've used the Texas Instruments TC245, which needs unusual voltages as well as multiple clocks, and all I can say is to do what the data sheet specifies and it should work.
     
  5. bxh

    Thread Starter New Member

    Dec 31, 2012
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    Interesting.. I'll take note of that if/when I can get the CCD working.

    I've worked with quite a few sensors and ICs myself, but somehow I have a feeling this one might just require a little more attention than usual.

    What other CCDs or image sensors have you worked with, if I may ask? I intend to move to an area CCD after I've gotten sufficient experience with linear ones.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    CCDs are somewhat difficult to use so don't expect an easy design. The data sheet states that all clocks are 5V. The trick is to meet all the timing requirements for the clocks as shown in the timing charts on page 7 and 8 of the data sheet. CCDs are particularly finicky about that since the clocks are pushing analog charges around, not just doing digital stuff.

    Also the output is not a smooth analog signal but includes switching pulses, as shown on page 5 of the data sheet, thus you typically do a correlated-double-sample of the output to extract the signal and minimize the noise.
     
  7. davebee

    Well-Known Member

    Oct 22, 2008
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    I've only used a couple of photodiode arrays besides the TI CCD 2D array: the TAOS TSL1401R CCD array and an ancient EG&G Reticon photodiode array. The Reticon diodes are switched, I think, rather than shifted, so it's not a CCD, but the results are about the same.

    But like I said, I'm not an expert; I've set these up and used them for a couple of projects, but that's it.

    I used the TAOS array on a mechanical scanner to try to digitize a page of text from a book, and that's where I had such trouble getting smooth and even lighting.
     
  8. bxh

    Thread Starter New Member

    Dec 31, 2012
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    Thank you! I'll just test the TCD1703C when it arrives and hope for the best then.
     
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