22 February 2008

More on the Mystery CCD

Yesterday I posted about a mystery CCD that I found in a flatbed scanner. It has no part number on it; all I knew was that it has 22-pins. I was hoping that it was like an LCD module---multiple vendors but a single footprint. Sadly, this is not the case.

Proof by counterexample: Toshiba produces at least two 22-DIP CCDs with incompatible footprints: the TCD1707D and the TCD2905D. From my analysis below, I now know that this CCD is neither of those.

I pulled out the continuity tested and started tracing connections. Here's what I've found:

  1. GND
  2. GND
  3. buffered input 1
  4. GND
  5. buffered output 1
  6. +12V
  7. GND
  8. buffered input 2
  9. buffered input 2 (8 and 9 are the same)
  10. GND
  11. GND
  12. GND
  13. odd, see below
  14. buffered input 3
  15. +12V
  16. GND
  17. buffered output 2
  18. buffered output 3
  19. GND
  20. buffered input 4
  21. GND
  22. GND
By "buffered input," I mean that the pin is driven by a 74HC04 inverted, through a resistor. By "buffered output," I mean that the pin is fed into a simple transistor inverter. By "odd", I mean that two '04 inverters are put in series and drive themselves through a capacitor. The output also drives this pin through a resistor.

Since this device has three outputs, I infer this is a color CCD. I suppose I could have read the packaging on the scanner, but I threw it out before I thought to check.


kerry said...

Hi... this doesn't help you too much, I mostly wanted to say hi. I do happen to have stumbled on a CCD myself recently though, taking apart a digi cam. I also live in Brooklyn and am thinking about projects to do with it. You could have mine if you want though - you seem much more apt to finish your project. I don't know exactly what it is - from a CANON camera.
bunch of numbers on it... CK1-1056 might be the one...
email me I'll send you a picture of it.
like your blog a lot.

k.i.p. said...

I don't have any pointers either, but i just wanted to drop a line saying that i recently took apart a flatbed HP scanner and found one that looks exactly like that. the circuit board is slightly different but the CCD is in the exact same place.
My tip is look at the circuit board itself and make some inferences about the connections to it through the way it is connected to the board. on the back of mine i notice that a multitude are connected to a huge trace that is ground. i noticed that three sets are connected across the CCD
I havent thought of anything cool to do with mine yet, so you can have it if you want.

Dennis Ferron said...

The inverters connected together by a capacitor are almost certainly a primitive clock generator. Or (if there's no feedback) it could be to generate a time delay from one inverter to the next. But my bet is that it was just an easy way for them to make an oscillator because there were already extra inverters in the 7404 packages.

Nick Johnson said...

@ kerry -

Though I'm not interested in another CCD, I really like your paintings! You, sir, have one more subscriber.

@ kip -

Yeah, I'm trying to infer from the board layout. I just need more information about what those three inputs might be. I think it's safe to assume that the three outputs are red, green and blue in some order.

@ dennis -

I think I agree, though it seems weird. The circuit is effectively an RC oscillator, and thus isn't very stable. But, at the same time, the pixels need to be shifted out at a controlled rate. So, I can't figure out what role that oscillator would play in this circuit.