C.e. Test Booked For 14 Oct 2009


Phawx said:
Plus they can ship directly from Texas to all USA peoples. SCORE!
Good for the US, yes, but unfortunately, I meant all of North America, we in Canada might not get that direct shipping, nor Mexico.

On a side note, it is a legal grey area to ship from there, the parts came in with a certain stipulation that they'd be shipped back, for duty reasons. So to ship from Texas directly, kinda violates that agreement.

Edit for spelling
 
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ED's tester is right about the FCC rules. But just to be clear, it's not law to utilize FCC marking on products, companies choose to put bran some electronic devices with it. the most that many will say is that "This product complies with part 15 of the FCC". Like I said on this very thread, a non certified electronic device in the U.S. is considered illegal (end user phone jammers for ex.), uncertified meaning if they don't have FCC, they'd better at least be CE or ISO certified.
:)

This could very well be the final two months.

- And now for a video-
 
That shielding foil on the flex will affect the impedance of the traces on the flex circuit. Does this mean that the flex circuit needs a re-design?
 
Forgive me, but why would shielding affect the impedance of a cable. I don't think the shielding would be 'touching' the traces. Because that would short them.
 
Phawx said:
Forgive me, but why would shielding affect the impedance of a cable. I don't think the shielding would be 'touching' the traces. Because that would short them.
Because it absorbs high-frequency signals. Do you understand what impedance is?

http://en.wikipedia.org/wiki/Electrical_impedance
 
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Foil shielding is used in Category 6 Ethernet cables and Shielded USB cables with runs measured in meters, the LCD ribbon is mere centimeters. I seriously doubt that any impedance created by the shielding will cause any issues. I seriously wonder if it would even be detectable except by the most sensitive equipment.
 
Neko said:
Phawx said:
Forgive me, but why would shielding affect the impedance of a cable. I don't think the shielding would be 'touching' the traces. Because that would short them.
Because it absorbs high-frequency signals. Do you understand what impedance is?

http://en.wikipedia.org/wiki/Electrical_impedance


I just thought it was resistance. As-in the resistance innate from the cable. Not the foil *around* it. Also I forgot to add that impedance could be miss-match by soldering the ends as well. Which is why when making your own RCA cables, its recommended to use a *clamp* fitting instead of a soldered end. To ensure that both ends are 75 Ohms.

Another edit: But what does absorbing emitted frequency have to do with the impedance of the wire? And please don't link to wiki. I am being quite serious. If I have a pipe and I try to force water through it, how much water I can force through it is the impedance, as in the pipe is stopping me from putting more water through. If water starts to seep outside of the pipe I can put a sponge on the outside of the pipe to absorb excess water, but I am still able to push the theoretical amount of water through this pipe.

That is how I understand it. If I am wrong please explain.
 
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Phawx said:
Another edit: But what does absorbing emitted frequency have to do with the impedance of the wire? And please don't link to wiki. I am being quite serious. If I have a pipe and I try to force water through it, how much water I can force through it is the impedance, as in the pipe is stopping me from putting more water through. If water starts to seep outside of the pipe I can put a sponge on the outside of the pipe to absorb excess water, but I am still able to push the theoretical amount of water through this pipe.

That is how I understand it. If I am wrong please explain.

This is a seriously complex topic. A couple of relevant links to read up for those who are interested:

http://en.wikipedia.org/wiki/Stripline
http://en.wikipedia.org/wiki/Transmission_line

Your hose pipe analogy isn't really up to the job. However, imagine the pipe is made of thin rubber, and you are not sending a steady stream of water through it, but are actually turning the tap up and down quickly. This generates pulses or water on top of a continous flow (like clock edges in a circuit). As the water comes out of the tap in a little burst, you can imagine it will stretch the rubber of the pipe (both width-ways, and maybe even length ways. I hope you can see that after flowing through a longer length of this pipe the sharp waves you put in at one end might get smeared out a bit by the time they get to the other end. You haven't lost any water, or even much energy, but the signal has been affected. Trust me - this is close enough what happens...

Now imagine you lay this pipe on top of a shallow puddle. Pulses flowing through the pipe might cause ripples to spread out through the puddle. Place another (empty) pipe close to the first one on one side, and what happens is that the ripples bounce off the 2nd pipe, maybe moving it a bit in the process, and the waves on the far side will be much smaller. This is the shielding effect which a sheet of foil buys you. now, it happens that the material surrounding the pipe does affect whats inside the pipe. If we surround our original rubber pipe with titanium tube, not a lot of signal leaks out, and maybe we manage to improve the quality of the puses we were trying to send though it. Pinch the pipe slightly to restrict it at a point, and you get reflected waves going backwards against the flow!

The key point is that a set of conductors have tiny amounts of distributed inductance and capacitance, in addition to resistance. For continous current this isn't a problem but for quickly changing current or voltage there is an effect (which is mathematically very simple, but very difficult to calculate or guess). That effect can be changed significantly by changing the conductors, or even the non-conducting material in-between.

If you imagine an inductor and capacitor connected as an oscillating circuit (a flywheel on an axle with a dot on the edge), a transmission line is almost like un-winding it, your flywheel is running across the floor.
 
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Thank you for the pulsing analogy. I am not an electrical engineer even in the slightest of sense, but I enjoy having at the very least a shallow understanding of the topic. By definition, I understand capacitance in inductance. I will ask a question along these lines as well, but first I had another question if you wouldn't mind answering in analogy form. ATA cables which were 40-pin and went to 80-pin around Ultra ATA-3 or 4 (it's been awhile) and the only thing they added was grounded cables along every other pin.

Using your pulsing analogy, these floating ground cables were added so that the pulses wouldn't interfere with it's nearest neighbor...hmm maybe this isn't the best to use. Basically what I am trying to get at, is why would shielding "pinch" the pipe?

Edit: Thanks for your time.
 
Phawx said:
Thank you for the pulsing analogy. I am not an electrical engineer even in the slightest of sense, but I enjoy having at the very least a shallow understanding of the topic. By definition, I understand capacitance in inductance. I will ask a question along these lines as well, but first I had another question if you wouldn't mind answering in analogy form. ATA cables which were 40-pin and went to 80-pin around Ultra ATA-3 or 4 (it's been awhile) and the only thing they added was grounded cables along every other pin.

Using your pulsing analogy, these floating ground cables were added so that the pulses wouldn't interfere with it's nearest neighbor...hmm maybe this isn't the best to use. Basically what I am trying to get at, is why would shielding "pinch" the pipe?

Edit: Thanks for your time.
Yes, generally having a grounded conductor between signal lines might reduce the cross talk interference between adjacent conductors. Maybe it isn't that simple though, since the ground wires arn't ground in a very convincing sense. Maybe the extra wires actually provide a better return path for the signal. I'd want to do some measurements to be sure!

The shielding can change the characteristic impedance of a transmission line because it adds capacitance between the conductors, and the impedance is affected by the ratio of inductance and capacitance per length. In my analogy, the puddle is free space outside of the flexi (waves usually need a medium, except electromagnetic waves which work in a vacuum). if the puddle is rectangular, it's effect on the pulses in the pipe are uniform all the way along. If the puddle is non-uniform, the little ripples in the puddle get focused back onto the pipe in a more intrusive way. Messy - and I think that's about as simple as it can be...
 
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The impedance of a system is determined by the geometry, and the dielectric constant of the insulators surrounding it.

A transmission line is a system where the geometry & dialectic constant are adjusted such that it has a particular impedance. (think coaxial cable, twinlead, twisted pairs etc).

The nice thing about a transmission line is that if you stick a resister across one end with a resistance that matches the characteristic impedance of the transmission line (say a 75 ohm resistor at the end of a 75 ohm coaxial cable), the other end will look exactly like a resistor with a resistance that matches the characteristic impedance at all frequencies to whatever is driving the cable. This is a very easy load to deal with.

The nasty thing about transmission lines is that if that resistance at the end (aka a termination) does not match, the signal will reflect back up the cable back to the source, and interfere with itself.

Do electronics long enough, and you will learn that every wire behaves like a transmission line weather you want it to or not, so you learn to design it as such.

About the only time you can ignore this behavior is when the wavelength of the highest frequency in the system is substantially longer than your wire. (think audio)

Since the flex has to be rolled up to fit through the hinge, the traces must be several inches long. The signals in the flex are carrying uncompressed digital video, so the frequencies will be high. Shielding the cable, may fix the RFI issue, but kill the ability to display video by causing an impedance miss match.

This is why I asked if the flex would need a re-design.
 
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