Best practices for board layout???

gmikol · 9th February 2006, 12:19 AM

Having gotten bit by the DIY bug, and with plans to build active 2-way and 3-way systems, I downloaded a copy of Eagle and got started.

I quickly discovered, though, that I don't know a #!%!#% thing about audio PCB layout. Need a 600MHz embedded SRAM? I can help. Lay out an active crossover?? No clue. In my world, everything is drawn pretty much as close to minimum as possible, and parasitic coupling to the power supplies is generally a good thing. Inductance is a non-issue.

So...does anybody out there have some good links or tips you can post re: good layout practices for this sort of stuff? You'll have my deepest appreciation...

--Greg

Leolabs · 9th February 2006, 12:44 AM

try to search on"PCB layout technics".

gmikol · 9th February 2006, 04:13 AM

I thought I'd try an example. Here's a battery-powered balance mic pre with phantom power. Schematic and layout. Feedback on the design itself and the layout are both appreciated.

--Greg

gmikol · 9th February 2006, 04:14 AM

The board...it's 2.75in x 1.5in

--Greg

pinkmouse · 9th February 2006, 09:34 AM

Hi Greg

A couple of points for your delectation. Just the way I would do things though, everyone has their own way of laying out a circuit on a PCB.

Firstly, power. Currently, your power rails are all over the board. I would move the PSU section to the right hand side of the board, then just run two parallel rails right under the ICs. Keep them close, to reduce radiated noise, and as short as possible. It wouldn't hurt to add a 100nF film decoupling cap as close as you can get it to each IC's power pins.

Secondly, layout. Quite often, I play with the schematic for a while, getting things as neat as possible, then try and emulate this on the PCB, so the parts layout on the PCB roughly follows the schematic. Try to keep logical blocks of the circuit together, rather than scattering them all over the PCB wherever they fit.

Hope that helps!

Curmudgeon · 10th February 2006, 12:46 AM

I agree completely with Pinkmouse. I'd just mention that the ground plane is a good idea; and there are no isolated islands. And having in and outputs separated at opposite ends of the board as you have is good practice too.

But mostly I wrote this so I could try the nod smiley.

gmikol · 10th February 2006, 05:56 PM

I started playing around with PM's suggestion last night. Don't have anything done yet, but it seems to force the layout into a long, skinny shape. I'm trying to jam it onto a small panel along with other stuff that's going to Olimex. So I'm kinda size constrained. I'll post back when I've fixed the layout.

But I guess the bigger question is...for a battery-powered application, is my original layout really that bad? I mean, "raidiated noise" from the PS tracks should be virtually non-existent in a battery supply, no?

Thanks for the input--

Greg

9th February 2006, 12:19 AM	#1
gmikol diyAudio Member Join Date: Oct 2005 Location: Vancouver, WA	Best practices for board layout??? Having gotten bit by the DIY bug, and with plans to build active 2-way and 3-way systems, I downloaded a copy of Eagle and got started. I quickly discovered, though, that I don't know a #!%!#% thing about audio PCB layout. Need a 600MHz embedded SRAM? I can help. Lay out an active crossover?? No clue. In my world, everything is drawn pretty much as close to minimum as possible, and parasitic coupling to the power supplies is generally a good thing. Inductance is a non-issue. So...does anybody out there have some good links or tips you can post re: good layout practices for this sort of stuff? You'll have my deepest appreciation... --Greg

9th February 2006, 09:34 AM	#5
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Hi Greg A couple of points for your delectation. Just the way I would do things though, everyone has their own way of laying out a circuit on a PCB. Firstly, power. Currently, your power rails are all over the board. I would move the PSU section to the right hand side of the board, then just run two parallel rails right under the ICs. Keep them close, to reduce radiated noise, and as short as possible. It wouldn't hurt to add a 100nF film decoupling cap as close as you can get it to each IC's power pins. Secondly, layout. Quite often, I play with the schematic for a while, getting things as neat as possible, then try and emulate this on the PCB, so the parts layout on the PCB roughly follows the schematic. Try to keep logical blocks of the circuit together, rather than scattering them all over the PCB wherever they fit. Hope that helps! __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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9th February 2006, 12:44 AM	#2
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	try to search on"PCB layout technics".

10th February 2006, 12:46 AM	#6
Curmudgeon diyAudio Member Join Date: Nov 2005	I agree completely with Pinkmouse. I'd just mention that the ground plane is a good idea; and there are no isolated islands. And having in and outputs separated at opposite ends of the board as you have is good practice too. But mostly I wrote this so I could try the nod smiley.

10th February 2006, 05:56 PM	#7
gmikol diyAudio Member Join Date: Oct 2005 Location: Vancouver, WA	I started playing around with PM's suggestion last night. Don't have anything done yet, but it seems to force the layout into a long, skinny shape. I'm trying to jam it onto a small panel along with other stuff that's going to Olimex. So I'm kinda size constrained. I'll post back when I've fixed the layout. But I guess the bigger question is...for a battery-powered application, is my original layout really that bad? I mean, "raidiated noise" from the PS tracks should be virtually non-existent in a battery supply, no? Thanks for the input-- Greg

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