pcbpcb-design
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Why wiggle nearby tracks on a PCB?
I was looking at a Raspberry Pi that a friend got today and noticed some weird traces on the board. I'm wondering why they were designed this way. Here is the best picture I could find of them.
There are a few sawtooth like traces that can be seen just above the HDMI and coming out from the IC.
My hypothesis is that the FPGA in the schematic is drawn as multiple sub-components along the lines of U51A, U51B, U52C, etc. U52C was intended as U51C, that's the error. Even though there is only one sub-component of U52 present, Eagle adds the whole IC to the board.
** I've made up the designators U51 and U52. The images in the O.P. have low resolution, and the designators aren't readable. I'm guessing that slender vertical component on the left is the connector, and the group of components on the right is the FPGA split into multiple sub-components.
A few thoughts:
Edit: Proof that you have the polarity reversed!
So I took a close look at your battery, and at the 1000C module and at the JST 2-PH connector.
This is a closeup of a generic JST 2-PH connector. Don't mind the colors of the wires as this is just a picture from the Internet. What's important is: You can clearly see that when the 'springs' that hold the contacts in the connector are on top, the '|' and two 'bumps' that hold the connector in the receptacle are on the bottom.
This is a closeup of the Adafruit 1000C module. The '|' and the bumps are on top, so the 'springs' must be on the bottom. With the '|' on top, the + is on the right. Put the '|' on the bottom, and thus the 'springs' on top, the + would be on the LEFT.
Now here's a closeup of the picture you posted in your question. The 'springs' are clearly on top, and you can see on the bottom there is one of the 'bumps', that are on the same side of the '|'. So the '|' is on the bottom. 'Springs' on top, + should be on the LEFT, but is on the RIGHT!
So your polarity is indeed reversed! You can carefully lift the 'springs' and take the contacts out. Then you can put them back in the right place. Be careful not to bend the 'springs' too far, as they are only plastic, and easly break off. Also make sure you don't accidentally short-circuit the battery when both contacts are out.
Hope this helps!
Update: I just saw they actually have a warning on their website for third party batteries with the polarity reversed!
How do you intend to charge the battery? Via the 1000C? Because that module can only charge with 1000mA max., so charging your battery (when completely discharged) will take more than 24 hours. I don't even know if you can charge a Li-Ion/Li-Po battery with less than 0.5C. But that's a completely different topic anyway...
Best Answer
Sometimes snake traces are used to ensure that parallel traces for a data bus all have the same length. This minimizes the phase difference between the signals. I can't see very clearly in the picture, but if the traces are smooth curves I'm betting this is the reason.
These are typically only used in very high speed designs where tiny signal delays and phase differences make a difference, the HDMI interface probably falls under that category. Also as mentioned below, differential signaling is another instance where phase differences between the signals can be very detrimental.