Author Topic: Why am not able to get a grasp of PCB designing?  (Read 15777 times)

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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #50 on: November 15, 2019, 04:42:17 am »
The maximum voltage across the resistor. This of course depends heavily on where it is used, in most cases the power will be very low except for resistors used for current sensing and such.

Ok, so I should calculate the power rating of each resistor.
 Just to check if I am doing it right,

The resistor R11 on USB C is 10k. The maximum voltage it will see is 12v. The power rating of the resistor using the formula P=V2/R gives, 1/100 Watt. Is that correct?
How do I determine the power rating for the resistors where I'm not sure about the voltage it will see, like the current sense resistor or the R2 114k on the RSET pin?

Thanks
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #51 on: November 15, 2019, 05:11:19 am »
Yes.  :)

First thing I spotted, top 2 resistors by the switch....rotate them vertical for better connectivity/easier routing.
While the purists like every device group orientated the same sometimes it's easier to flip and swap to make for easier routing.
Apply similar thinking throughout the PCB and you'll be staggered how much easier things become.

Shift some component designators off the device so it's easier for us to pick a # that should be moved/flipped etc.
Stack
them
alongside
somehow
like this. :)

Done. Here is a picture
872186-0

Any more suggestions?

Edit : After taking the pic, I rotated the resistors R5 and R9 to make connections easier.
« Last Edit: November 15, 2019, 05:15:21 am by redgear »
 

Offline ebastler

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Re: Why am not able to get a grasp of PCB designing?
« Reply #52 on: November 15, 2019, 06:04:20 am »
That latest placement looks pretty good, I think. Only change I would suggest: Give yourself a bit more room around the main IC by making the PCB larger in the vertical direction. The passives above and below are very close to the IC, so you might run out of room for the traces. You can always push things closer together later -- while I have not used KiCAD, I read that its push-and-shove router works quite well.

Time to start the routing! (Which will probably lead you to some more tweaks in the placement once you look at the routing details.)
 

Online tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #53 on: November 15, 2019, 07:09:55 am »

Edit : After taking the pic, I rotated the resistors R5 and R9 to make connections easier.
:-+
Quote
Any more suggestions?
Lots, really lots.
More of the above, much more.
You are gaining the vision required but keep looking and looking and after an autoroute of two you will see more. Pick a net or two and focus on getting them the best you can the rinse and repeat with other nets.

At a glance a few simple pointers.
Flip and lower D6 so to run the GND trace around the top to J3.
Flip TH1 and R8 then you have just one trace to sort out the routing for and lift it a little and run the trace along the edge of the board.
Move Q2 to between Q4 and U1.
Consider rearranging Q1-4 and associated components to allow for easier/better routing.
Don't bunch SMD passives too close to bigger components. (later you'll thank me.  ;) )
Tidy up labeling even though after routing you may need to do it again. Use same font size for all.

That's an hour of two's work to sort out and enough for now so to not piss you off too much.  :)

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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #54 on: November 15, 2019, 08:28:52 am »
I really appreciate you taking the time to guide me. Thank you so much.

Consider rearranging Q1-4 and associated components to allow for easier/better routing.
I planned to keep all the power FETs in one section. I will try rearranging it.

Quote
Don't bunch SMD passives too close to bigger components. (later you'll thank me.  ;) )

Are you talking about the capacitor networks? Aren't they supposed to be as close as possible to the ICs?
And the LEDs, I cannot rearrange them since I planning the mechanical enclosure to have LEDs at the center.

Quote
Tidy up labeling even though after routing you may need to do it again. Use same font size for all.
That's an hour of two's work to sort out and enough for now so to not piss you off too much.  :)
Ok :-+
 

Online tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #55 on: November 15, 2019, 08:58:40 am »
I really appreciate you taking the time to guide me. Thank you so much.
No probs, I just happened to the Johnny on the spot.  :)
I don't do much now but really got hooked on making a nice job of PCB's for a while as with a little bit of practice it gets quite addictive. After a bit you can pick holes in most ppls work and see how you might have done it better. You can spend days on even a modest PCB, layout correction after another then a heap of time interactive routing but guys that can really make CAD programs talk spend a bit of time on the global settings then the program does most of the work.
Still you learn a lot doing it longhand as it were then with the good CAD programs let the settings made save you the hassle.
Don't bunch SMD passives too close to bigger components. (later you'll thank me.  ;) )
Are you talking about the capacitor networks? Aren't they supposed to be as close as possible to the ICs?
No, it's just a general statement for C's and R's.
Earlier I said always to consider rework so if placement doesn't allow getting an iron to a component how do you replace just that component should you need to ? For first up prototypes this can be important as there's often component substitutions to make the circuit work as planned.
Yeah I know, drag out the hot air you'll say but what about all the surrounding components when you could have done it with an iron. BTW if you haven't got a K style Hakko type tip get one ! Some call them a skew but either way they allow the ability to heat both ends of SMD passives for shit easy removal.
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Offline Rerouter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #56 on: November 15, 2019, 09:11:32 am »
The capacitors should be as close as reasonable, (minimizing inductance, loop area, all that jazz) but if the capacitor is so close to the IC or another capacitor that it is a right pain to prevent shorting or fit, then it kind of hurts the benefit of the closer positioning, `

remember the loop for decoupling includes any via's, and the ground routing on the other side, this is why decoupling caps on really fast devices (high switching frequencies) will have the decoupling capacitor practically straddling the vias for a short run back to the pins that it needs to decouple, or in some cases routed with the return path coupled as close as possible,
 
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Offline NivagSwerdna

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Re: Why am not able to get a grasp of PCB designing?
« Reply #57 on: November 15, 2019, 09:52:43 am »
re: Image above

Much better.  Imagine you are trying to unknot a ball of string...

By flipping the components you can untwist the string... all 3 parts in the top left are obvious candidates.
 
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Offline ebastler

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Re: Why am not able to get a grasp of PCB designing?
« Reply #58 on: November 15, 2019, 03:11:06 pm »
Give yourself a series of tasks.

It's best to actually read the thread, not just the title of the first post, before replying.  :P

And no, I'm feeling fine, thank you very much.
Interesting choice of user name...
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #59 on: November 16, 2019, 05:31:44 am »
You can spend days on even a modest PCB, layout correction after another then a heap of time interactive routing but guys that can really make CAD programs talk spend a bit of time on the global settings then the program does most of the work.
Still you learn a lot doing it longhand as it were then with the good CAD programs let the settings made save you the hassle.
After I finish this PCB, I will see what all settings I can play with to make this job easier....
In your last post you suggested me to consider rearranging the FETs, but I am not able to find a better place.  :-BROKE
Quote
No, it's just a general statement for C's and R's.
Earlier I said always to consider rework so if placement doesn't allow getting an iron to a component how do you replace just that component should you need to ? For first up prototypes this can be important as there's often component substitutions to make the circuit work as planned.
Yeah I know, drag out the hot air you'll say but what about all the surrounding components when you could have done it with an iron. BTW if you haven't got a K style Hakko type tip get one ! Some call them a skew but either way they allow the ability to heat both ends of SMD passives for shit easy removal.
Thanks for the recommendation, I'm actually planning to invest on a good soldering station. :)

The capacitors should be as close as reasonable, (minimizing inductance, loop area, all that jazz) but if the capacitor is so close to the IC or another capacitor that it is a right pain to prevent shorting or fit, then it kind of hurts the benefit of the closer positioning, `

remember the loop for decoupling includes any via's, and the ground routing on the other side, this is why decoupling caps on really fast devices (high switching frequencies) will have the decoupling capacitor practically straddling the vias for a short run back to the pins that it needs to decouple, or in some cases routed with the return path coupled as close as possible,
Thank you, another reason for me placing them very close is they looked better that way.
re: Image above

Much better.  Imagine you are trying to unknot a ball of string...

By flipping the components you can untwist the string... all 3 parts in the top left are obvious candidates.
Thanks, I can't move the USB ports and the switch, I placed them according to their mechanical orientation.
 

Online tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #60 on: November 16, 2019, 06:18:34 am »
In your last post you suggested me to consider rearranging the FETs, but I am not able to find a better place.  :-BROKE
Well, I hoped you could see the hole just begging for Q2 to be placed in it !  :-//
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Online tautech

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Re: Why am not able to get a grasp of PCB designing?
« Reply #61 on: November 24, 2019, 09:34:14 am »
OK redgear, have you given up or too shy to come back and show off your efforts ?  :-//
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Offline max_torque

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Re: Why am not able to get a grasp of PCB designing?
« Reply #62 on: November 24, 2019, 06:04:21 pm »
Quite possibly a bit late, but one "trick" that seems to work repeatibly is to orient "square" micros at 45 deg, in this way, they can have traces come off in two directions without requiring as much "packing in" to the space.  In reality, unless you have a perfectly square pcb, and can use all 4 sides around the micro, this 45 deg layout tends to be easier to route ime!
 
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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #63 on: November 25, 2019, 04:53:57 am »
OK redgear, have you given up or too shy to come back and show off your efforts ?  :-//
Nope, I haven't given up neither shy. I am making some changes to my schematic, replacing the controller with a better one. So, will post an update very soon.

Quite possibly a bit late, but one "trick" that seems to work repeatibly is to orient "square" micros at 45 deg, in this way, they can have traces come off in two directions without requiring as much "packing in" to the space.  In reality, unless you have a perfectly square pcb, and can use all 4 sides around the micro, this 45 deg layout tends to be easier to route ime!
But I am able to make only 90deg rotations on Kicad.
Edit: Just found out how to rotate footprints 45deg. Thanks for the trick
« Last Edit: November 25, 2019, 05:00:10 am by redgear »
 
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Offline Rerouter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #64 on: November 25, 2019, 07:43:17 am »
you can set the rotation step size to whatever you wish, I usually use 22.5 degrees, you can also draw curvy traces with kicad with a little work if you need to work around very compact spacing. (free angle mode, and replace the corner twice to get very close to a smooth curves
 
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Offline ebastler

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Re: Why am not able to get a grasp of PCB designing?
« Reply #65 on: November 25, 2019, 09:29:18 am »
you can also draw curvy traces with kicad with a little work if you need to work around very compact spacing. (free angle mode, and replace the corner twice to get very close to a smooth curves

That looks rather vintage! Just as wobbly as the classic taped layouts. ;)

I can see the benefit this might have in some tight spots. But without full support in the PCB layout software -- splines or such to create smooth curves, and precise matching of the shape of neighboring traces in push-and-shove mode -- it seems very burdensome, and the result is not as neat as I would like.
 

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Re: Why am not able to get a grasp of PCB designing?
« Reply #66 on: November 25, 2019, 09:56:25 am »
It seems you're routing some differential signals, going by the net labels on the top right socket (DPA1, DMA1). You'll need to give these priority during routing. Make sure you rename the nets to DA1_P, DA1_N, or KiCad will not be able to figure out the routing pairs. I'm guessing you are going for a standard FR4 board with 1.6mm final thickness, that'll make correct impedance nigh impossible, but you should at least get the lengths matched. Should not be a huge problem for USB1 class speeds.
Everybody likes gadgets. Until they try to make them.
 

Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #67 on: November 25, 2019, 10:09:16 am »
It seems you're routing some differential signals, going by the net labels on the top right socket (DPA1, DMA1). You'll need to give these priority during routing. Make sure you rename the nets to DA1_P, DA1_N, or KiCad will not be able to figure out the routing pairs. I'm guessing you are going for a standard FR4 board with 1.6mm final thickness, that'll make correct impedance nigh impossible, but you should at least get the lengths matched. Should not be a huge problem for USB1 class speeds.
Thanks. Why shouldn't I use the DMA/DPA labels?
 

Online thinkfat

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Re: Why am not able to get a grasp of PCB designing?
« Reply #68 on: November 25, 2019, 10:41:30 am »
It seems you're routing some differential signals, going by the net labels on the top right socket (DPA1, DMA1). You'll need to give these priority during routing. Make sure you rename the nets to DA1_P, DA1_N, or KiCad will not be able to figure out the routing pairs. I'm guessing you are going for a standard FR4 board with 1.6mm final thickness, that'll make correct impedance nigh impossible, but you should at least get the lengths matched. Should not be a huge problem for USB1 class speeds.
Thanks. Why shouldn't I use the DMA/DPA labels?

Quote
or KiCad will not be able to figure out the routing pairs

The interactive router in KiCad has a special mode for differential pairs, but you need to name the nets of the pair accordingly. They must end in "_P" and "_N".
Everybody likes gadgets. Until they try to make them.
 
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Offline jhpadjustable

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Re: Why am not able to get a grasp of PCB designing?
« Reply #69 on: November 25, 2019, 10:43:02 am »
+ / - are also acceptable. e.g. A1D+ and A1D-
"There are more things in heaven and earth, Arduino, than are dreamt of in your philosophy."
 
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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #70 on: November 25, 2019, 10:49:18 am »
The interactive router in KiCad has a special mode for differential pairs, but you need to name the nets of the pair accordingly. They must end in "_P" and "_N".

+ / - are also acceptable. e.g. A1D+ and A1D-

Thanks :)
 

Offline EEVblog

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Re: Why am not able to get a grasp of PCB designing?
« Reply #71 on: November 25, 2019, 10:55:09 am »
 
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Offline redgearTopic starter

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Re: Why am not able to get a grasp of PCB designing?
« Reply #72 on: November 25, 2019, 10:56:54 am »
Watch Dave:


I have another one:



Thanks Dave, I have watched both the videos. I am using KiCad and i'm finding it a bit different(and difficult) than Altium.
 

Offline EEVblog

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Re: Why am not able to get a grasp of PCB designing?
« Reply #73 on: November 25, 2019, 10:57:47 am »
Done. Here is a picture
(Attachment Link)

First thing I noticed was the cross on the rats nets for Q2 and Q4/Q3, I'd swap these so the rats net don't cross, then you can route directly.
 

Offline EEVblog

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Re: Why am not able to get a grasp of PCB designing?
« Reply #74 on: November 25, 2019, 11:00:08 am »
Thanks Dave, I have watched both the videos. I am using KiCad and i'm finding it a bit different(and difficult) than Altium.

You've done 90% of the work, which is the schematic, netlist, footprints, and component placement. Actually routing that board takes the same amount of time in any package, they are all basically the same productivity at that point with manual routing.
 


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