How to REALLY start designing PCBs?

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Re: How to REALLY start designing PCBs?

Postby CodeMonk » 25 Oct 2012, 23:16

Dirk_Hendrik wrote:
DrNomis wrote:.....actually I miss those newbie days..... :thumbsup


Hmmmm. preps the joy of discovering something new.....

but the frustration.... the endless frustration. Naah not that again :blackeye


I can't count the number of times I have designed a PCB from a schematic and forgot a part [smilie=a_doh.gif]
Usually because I rushed it.
Thats why I backtrace and fronttrace (is that even a word? It is now) everything now.
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Re: How to REALLY start designing PCBs?

Postby rocklander » 26 Oct 2012, 00:00

Nocentelli wrote:
Dirk_Hendrik wrote:What I should do is press print screen a few times next time and post the shots including comments...


That would be amazing (presuming you're serious, I know you're pretty dry)....

I'm personally strictly vero at the moment, but i'm eager to get started on some proper pcbs, especially now there seem to be some cheap-ish smallscale pcb fabrication online now. So far, I've opened Eagle a few times.... then closed it again.

I know I'm going against the grain here, but I had the same experience.. eagle just confuses the crap out of me.. I tend to use expressPCB cos (to me) it's more drag'n'drop / wysiwyg .. I just do the PCB (never bother with the schem) then in a paint type program haav ethe original schem and cross off the components as I add/connect them ... it's probably poor form to start out that way cos I still avoid eagle and it'd have been better character building to have learnt it, but I can do all I really want in expressPCB... still learning some of its tricks .
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Re: How to REALLY start designing PCBs?

Postby Duckman » 26 Oct 2012, 08:35

rocklander wrote:
Nocentelli wrote:
Dirk_Hendrik wrote:What I should do is press print screen a few times next time and post the shots including comments...


That would be amazing (presuming you're serious, I know you're pretty dry)....

I'm personally strictly vero at the moment, but i'm eager to get started on some proper pcbs, especially now there seem to be some cheap-ish smallscale pcb fabrication online now. So far, I've opened Eagle a few times.... then closed it again.

I know I'm going against the grain here, but I had the same experience.. eagle just confuses the crap out of me.. I tend to use expressPCB cos (to me) it's more drag'n'drop / wysiwyg .. I just do the PCB (never bother with the schem) then in a paint type program haav ethe original schem and cross off the components as I add/connect them ... it's probably poor form to start out that way cos I still avoid eagle and it'd have been better character building to have learnt it, but I can do all I really want in expressPCB... still learning some of its tricks .


If you take a little time to re-draw the scheme in ExpressSHC and link it to your ExpressPCB, then you can check all the nets and connections very easily, reducing your error margin substatially... why you don't do that? :scratch: At the end, you only need to be sure about your schemo and then your PCB will be ok.
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Re: How to REALLY start designing PCBs?

Postby rocklander » 26 Oct 2012, 08:52

cos I'm pretty lazy.. I actually enjoy the PCB layout part, so that's why I do it// doing schems don't thrill me at all..
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Re: How to REALLY start designing PCBs?

Postby Duckman » 26 Oct 2012, 09:38

Well... it's just a tool...
rocklander wrote: still learning some of its tricks .

... and a good trick :lol:
Tell me if you need some :thumbsup
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Re: How to REALLY start designing PCBs?

Postby Dirk_Hendrik » 26 Oct 2012, 11:28

rocklander wrote:I just do the PCB (never bother with the schem)


And there's a distinct different approach.

In my case the schem is the absolute basis. In the schem all connections are defined (naturally) nas well as component values and physical shape. From this a component file and a netlist is exported. These 2 are imported in the PCB design application which shows the physical shapes and how components are connected. Therefore when I think I am finished the application can tell me if I missed connections. If the schem is corrrect the PCB will be too (from a connection perspective) If a component is forgotten that happened in the schem already.

Or, in essence,
Graphical applications, wether they are PsP, Corel, paint, illustrator or whatever are not PCB design tools but workarounds.
Sorry. Plain out of planes.

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Re: How to REALLY start designing PCBs?

Postby rocklander » 26 Oct 2012, 12:48

agreed.. I'm a results based person.. others are process based. to each their own :D
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Re: How to REALLY start designing PCBs?

Postby Intripped » 26 Oct 2012, 15:39

can i ask something about ground and power lines routing?
i know that ground routing is not critical for pedal effects, but anyway i'd like to have some guidelines to understand how the perfect routing should be

star grounding is the optimum, and ground plane are very good too (not sure about power planes...), but let's say that we only have one-sided PCBs and star ground is too difficult to obtain: where to connect input and output signal grounds? and +9V? chassis ground? supply ground? LED ground?

i think that an example would help - an unrealistic example just to understand the undergoing principles:
take the big muff circuit (see image) and imagine to have the PCB routed exactly like the schematic - so you have the circuit that goes from left to right - now, where would you connect the supply ground and +9V? on the left or on the right of the circuit? or maybe in the middle?
and the input signal ground? on the left? the output-ground on the right?
chassis (box) ground?
LED ground? is it ok to connect it on the supply jack? or there's a better position?
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Re: How to REALLY start designing PCBs?

Postby Dirk_Hendrik » 26 Oct 2012, 21:18

Intripped wrote:can i ask something about ground and power lines routing?
i know that ground routing is not critical for pedal effects, but anyway i'd like to have some guidelines to understand how the perfect routing should be

"less critical", not "not critical".
Imagine a LED that switches on or a LFO circuit that switches state. Imagine that circuit sharing a ground line with an amplifying circuit for few centimeters to the point where the DC power supply enters the stompbox.*
When that LED or LFO switches the change in current draw (and corresponding voltage drop) over that trace, while having only a few 10's of ohms of resistance can be very audible in the amplified signal becasue of the sudden supply voltage change of the amplifier stage.

*?
Yes. Ideally one wants to consider his power supply having such an low output impedance that it will "suck up" all power supply noises. In the non ideal world there's usually a few meters of cable in between the supply's filter caps and DC regulation. There may be some daisy chain in place that feeds other effects and their own noise. One cannot take this into consideration, other than by adding a power supply decoupling cap at the DC input.

Intripped wrote:star grounding is the optimum, and ground plane are very good too (not sure about power planes...),

Even in the few 100's of kHz's star grounding starts to decrease in performance rapidly already. Star grounding might be considered "good" from an audio frequency perspective but was obsoleted years ago already with digital stuff and incresing clock frequencies. If you introduce a noise, provide a good, low impedance return path close to it. For instance a ground plane.

Ground planes are part of the subcollection of power planes. If you go 4 layer, have a ground plane, VCC plane and 2 signal layers.

Intripped wrote:but let's say that we only have one-sided PCBs and star ground is too difficult to obtain: where to connect input and output signal grounds? and +9V? chassis ground? supply ground? LED ground?


Indeed. Back to one layer :thumbsup
Input ground:
What are you going to do with your signal? You''ll probably going to amplify/buffer it first? This means you're going to amplify a voltage potential at the input compared to a reference (ground). Now if that "ground" needs to travel say 10cm from a central grounding point upto the reference of that amplifier that's another 10cm of increased impedance and noise pickup. So, preferably keep both input and reference connection as friggin short as possible.

Output, same thing but less inmportant in FX as they usually drive with a low impedance output.

Chassis and LED ground,
At the entry point of your power supply. That's the supply ground.



....there's shitloads of exceptions to be brought up to all above that happen to work, that happen to "sound good" etc.... but suddenly don't happen to work on a Bogner, or are "terrific with Fenders" but "Suck with Marshalls". Very smart engineers tried to make designs pedals in such a way they would respond the same, as much as possible, regardless of the amps used. Unfortunately guitarists are guitarists and the immediate complaint was "toan suck". Immediately after this far less talented "engineers" started to remake these designs with all the "situation vulnerability" again and marketed them as boutique and "full of toan" and "made by real musicians".
Sorry. Plain out of planes.

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Re: How to REALLY start designing PCBs?

Postby Duckman » 26 Oct 2012, 21:31

Usually, I trace everything and use the rest of the one sided board as a ground plane, like the picture (Kapputepala's Roger Mayer's VoodooVibe) on ExpressPCB
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Re: How to REALLY start designing PCBs?

Postby Intripped » 26 Oct 2012, 22:38

WOW !
thanks a lot for the very detailed answer Dirk! :thumbsup

please have a look of the image below:
i have placed the input and the output signal grounds, the led ground and the chassis ground.
...but i'm still not sure about where to connect the +9V and the ground coming from the decoupling capacitor

i'm thinking about some grounding principles, applied in tube amplifiers.
i've learned a lot on this pdf: http://www.valvewizard.co.uk/Grounding.pdf

so I think that the best position for +9V and ground is at the right of the circuit, am I right?

thanks again!


EDIT - I see now your answer Duckman
yes, i see that this kind of solution is good in many ways, but it could be that the ground plane is like a "trace" in some points of the PCB, and it could also be that components of very different parts of the circuit share this same "trace" ...and also some ground loops may occour, I think
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Re: How to REALLY start designing PCBs?

Postby Duckman » 27 Oct 2012, 01:01

Intripped wrote:it could be that the ground plane is like a "trace" in some points of the PCB,


Not a problem

Intripped wrote:it could also be that components of very different parts of the circuit share this same "trace"


If they are grounded, yes, should be

Intripped wrote:and also some ground loops may occour, I think


Where?
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Re: How to REALLY start designing PCBs?

Postby Intripped » 27 Oct 2012, 03:45

Duckman wrote:
Intripped wrote:it could be that the ground plane is like a "trace" in some points of the PCB,


Not a problem

Intripped wrote:it could also be that components of very different parts of the circuit share this same "trace"


If they are grounded, yes, should be


you got this as two different considerations, but the real point is the second one, the first being just an assumption.
if two components of different parts of the circuit, for example only the first transistor and the last potentiometer in the big muff circuit, would share this "trace", well i think this solution is not optimal. and that's the point of all my questions about ground routing

Duckman wrote:
Intripped wrote:and also some ground loops may occour, I think


Where?


i'm not referring to the PCB that you posted - but ground loops may occour with this kind of grounding.
look at the attached PCB, if you consider the definition of a ground loop (A ground loop happens when connectors are connected together through two separate grounding paths) if i'm not wrong there is more than one ground loop in this PCB

...well this is what i think at least... i'm not 100% sure about what i've just said
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Re: How to REALLY start designing PCBs?

Postby Duckman » 27 Oct 2012, 19:31

Got your point, Intripped and sorry for my noobness.
I clearly understand ground loop between different devices, but ground loop inside a single device, just don't get it... my fault.
In the other hand, so far, I've just built about 25, 30 pedals using that kind of ground plane distribution but, so far, I never had any of the problems associated with the presence of a ground loop. Do I have to assume that I'm just a lucky guy or, a ground loop in a low voltage device like a 9v pedal is not that relevant?

Thanks for your words :thumbsup
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Re: How to REALLY start designing PCBs?

Postby Intripped » 27 Oct 2012, 21:04

well, my opinion is that these ground loops aren't a big problem: they are very small, and the smaller they are the less noise they can introduce.
if i have well understood, a ground loop works like an antenna, so if you have tiny antennas in a shielded enclosure all you can get is electromagnetic fields generated by the circuit itself. maybe clock noise or LFO ticking could be an issue; let's see if Dirk has something to say.
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Re: How to REALLY start designing PCBs?

Postby Duckman » 27 Oct 2012, 23:40

Nice... Dirk? :lol:
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