Designing PCBs is hard

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: luketeaford, Joe., lisa, Kent

User avatar
Tombola
Super Deluxe Wiggler
Posts: 1878
Joined: Sun Jan 23, 2011 11:33 am
Location: London, England

Designing PCBs is hard

Post by Tombola » Wed Mar 14, 2012 6:51 am

So, I've made the circuit (this: )
I've put the schematic in Eagle
I've created new symbols and packages
I've sent off a simple double sided PCB to China just to make sure I know how the process works.
I've tweaked the drill sizes
I've put all the components on the board, in more-or-less self contained circuit elements
I've got everything to fit
I've poured a ground plane on the bottom
I've routed fatter +12v and -12v channels

Then I hit autoroute and it gets to 90%, leaving a bunch of airwires. I move a few components around, I fiddle with the settings, it gets to 93%. I look where the airwires are going, and can see why the computer can't work it out...

All the forum posts say "real men don't use an autorouter", but I can't imagine how long it would take to manually draw in 56 connections. It's a lot harder than threading little wires through perfboard!

Any tips on how to win with routing, auto or otherwise? Is my board just too dense?

Should I spend more time on component placement, to try to minimise all the airwires?

Where to start?

Maybe I just need to RTFM, that's got me this far...

Here's the board pre-routing, showing all the airwires. Looks like a nasty to-do list to me.

Image
Last edited by Tombola on Wed Mar 14, 2012 7:14 am, edited 1 time in total.

User avatar
BugBrand
Knowledge of Bugs
Posts: 7309
Joined: Tue Jul 15, 2008 11:59 am

Post by BugBrand » Wed Mar 14, 2012 6:57 am

Only 56 connections?
Pah!

There's a reason I refer to this routing process (no autorouting here) as playing around with 3d spaghetti.

But remember -- with this method, you only have to do the hard-graft once, then everything rolls smoothly (well, until you decide to change something on the PCB or 'update' the design)

Good luck with it Tom!

User avatar
L-1
Super Deluxe Wiggler
Posts: 2171
Joined: Wed Dec 14, 2011 8:20 am
Location: Belarus
Contact:

Post by L-1 » Wed Mar 14, 2012 7:18 am

real men don't use an autorouter
:hyper:

the secret is correct parts placement. I redraw with autorouter many times, move parts again and again, and play with autorouter settings to achieve good results. but i don't use Eagle autorouter. I like better Freeroute.
This is some sort of art - PCB design.

BTW chips at the top are too close, make some clearance.

*edit* After autoroute I correct layout by hand because robots are not perfect.

ImageImage
Last edited by L-1 on Wed Mar 14, 2012 7:40 am, edited 2 times in total.

User avatar
Monobass
thonk.co.uk
Posts: 8803
Joined: Fri May 29, 2009 5:39 pm
Location: Brighton, UK
Contact:

Post by Monobass » Wed Mar 14, 2012 7:27 am

Keep us updated Tom cos I really have a sick desire to do this too later this year.
Thonk - CLICK HERE - Modular Synth DIY + Eurorack Accessories Store

User avatar
Joe.
Wired for sound
Posts: 4994
Joined: Sun Jan 30, 2011 10:58 pm

Post by Joe. » Wed Mar 14, 2012 7:50 am

Your going to need to spend hours and hours rotating different parts, inserting extra vias, maybe even adding 0 ohm smd resistors to add options; basically experimenting. That's half of the fun of PCB design :tu:

User avatar
Tombola
Super Deluxe Wiggler
Posts: 1878
Joined: Sun Jan 23, 2011 11:33 am
Location: London, England

Post by Tombola » Wed Mar 14, 2012 8:01 am

Thanks L-1 - SMD resistors on the backs of pots looks like a good idea.

Mounting holes are big grounded vias, right?

I'm very happy that your boards look like that - I was rather intimidated by Negativspace's incredibly neat and smart single sided BVP board: viewtopic.php?t=34483

Interesting to see how it was done in the good ol' days:
Image

User avatar
L-1
Super Deluxe Wiggler
Posts: 2171
Joined: Wed Dec 14, 2011 8:20 am
Location: Belarus
Contact:

Post by L-1 » Wed Mar 14, 2012 8:15 am

Mounting holes are big grounded vias, right?
This board mounts to panel with jacks, pots and switches but I made this holes to mount shield at the back.
I didn't made this board yet, will order prototypes run of 20 maybe next week.

User avatar
Navs
Super Deluxe Wiggler
Posts: 4185
Joined: Fri Sep 18, 2009 3:49 am
Location: Berlin, Germany

Post by Navs » Wed Mar 14, 2012 8:19 am

LoFi Junglist wrote:... That's half of the fun of PCB design :tu:
Fun?!

User avatar
megaohm
Super Deluxe Wiggler
Posts: 1897
Joined: Mon Jun 15, 2009 6:11 am
Location: Chicago, IL

Re: Designing PCBs is hard

Post by megaohm » Wed Mar 14, 2012 8:20 am

Tombola wrote: All the forum posts say "real men don't use an autorouter",
I'd re-phrase that as real artwork is not done by an autorouter.
Maybe I'm just close minded.
Look at those old Buchla pcbs. Curvy traces = beautiful.

Just start doing the traces. You will find yourself unrouting things and moving parts around. That's fine and normal.
The more practice you have the better able you will be in seeing the pcb in your minds eye.

The two 4015 CMOS chips are too close together.
www.MegaOhmAudio.com

Will work for pistachios

User avatar
lysander
Wiggling with Experience
Posts: 336
Joined: Wed Feb 01, 2012 7:26 am

Post by lysander » Wed Mar 14, 2012 9:08 am

Interesting, I too am planning on getting my hands dirty with PCB design later this year ( when I'm done refreshing my electrical engineering ).
I think I was being very naive about the process, imagining that it was the quick easy part after designing the circuit :sadbanana:
That's what you get from theory-oriented college degrees I guess, they tend to forget to teach you how to make your stuff work in the real world :lol:

User avatar
lizlarsen
Super Deluxe Wiggler
Posts: 2155
Joined: Wed Jan 13, 2010 1:45 pm
Location: Denton, TX

Post by lizlarsen » Wed Mar 14, 2012 9:39 am

Routing traces manually is way way easier than dealing with the autorouter in my opinion! Just have a plan going in, and break it up into little chunks. You've got a pretty densely packed board there, and thru-hole means that routing can be more difficult. Set things to a 10mil grid and do 10mil traces, don't be afraid to get them right up next to each other or use small vias. Try to have bottom-side traces go one way, and top-side traces the other way.

Usually I construct little circuit blocks as densely as my DRC will allow, route them independently, then place them on the PCB, route power, and then connect the blocks to each other. That's going to be difficult with thru-hole on this layout I bet. 56 traces goes by extremely fast. You can hide power and ground connections in eagle by entering the command "ratsnest ! gnd +12v -12v", etc. and then do the same (minus the ! symbol) when you want to show them again.

If you're finding it extremely difficult or impossible to squeeze your layout onto this board, you might want to go to a second PCB, and use 0.1" headers to connect the boards.

User avatar
negativspace
Manhattan Analog
Posts: 6576
Joined: Tue Apr 13, 2010 2:50 am
Location: Manhattan, KS, USA
Contact:

Post by negativspace » Wed Mar 14, 2012 9:44 am

FWIW the BVP board is double-sided. It was really tidy until this last revision where I crammed a DIP-8 and resistors in while shrinking it slightly. :deadbanana:

Part of the process for me is to go back even after the connections are all done and optimize traces. I don't use autoroute at all, either, I prefer to hand-draw them all. Probably a result of my design background.

User avatar
vozs
Wiggling with Experience
Posts: 291
Joined: Tue May 04, 2010 1:56 pm
Location: http://www.youtube.com/watch?v=nQPlFLtWDwM

Re: Designing PCBs is hard

Post by vozs » Wed Mar 14, 2012 9:50 am

Tombola wrote:So, I've made the circuit (this: )

Then I hit autoroute and it gets to 90%, leaving a bunch of airwires. I move a few components around, I fiddle with the settings, it gets to 93%. I look where the airwires are going, and can see why the computer can't work it out...

All the forum posts say "real men don't use an autorouter", but I can't imagine how long it would take to manually draw in 56 connections. It's
a lot harder than threading little wires through perfboard!
Real men have since long time figured out auto routers are a very, very complicated and advanced area of science.

PCB routing are an art and it takes a certain mind to think
in 3D particularly when drawing boards with 16 layers!
:bacon:

""Real"" autoroters are very expensive forget get them for free.
Where to start?
Learn to draw board without using net lists and auto routers.
As real men do! :omg:

User avatar
negativspace
Manhattan Analog
Posts: 6576
Joined: Tue Apr 13, 2010 2:50 am
Location: Manhattan, KS, USA
Contact:

Post by negativspace » Wed Mar 14, 2012 10:03 am

I laid out the Mutinator without even so much as a schematic, much less a netlist or autorouter... does that make me a real man? :hihi:

User avatar
Tombola
Super Deluxe Wiggler
Posts: 1878
Joined: Sun Jan 23, 2011 11:33 am
Location: London, England

Post by Tombola » Wed Mar 14, 2012 10:05 am

Ha, ignore my previous post and all this macho talk of hand carving boards out of raw fibreglass and homemade copper.

Removed the ground pour, pressed 'auto' and it went through first time.

I know, I know, there is still a lot of polishing to do, proper power lines, improved angles, removing totally superfluous resistors...

Image

User avatar
ultrashock
Veteran Wiggler
Posts: 565
Joined: Thu Jun 24, 2010 6:52 am
Location: Underhaven

Post by ultrashock » Wed Mar 14, 2012 10:11 am

yes, that's some sort of art, definitely...
Image

User avatar
JRock
InterGalactic Barbarian
Posts: 1767
Joined: Thu Dec 23, 2010 2:29 am
Location: PA

Post by JRock » Wed Mar 14, 2012 10:14 am

Centralize everything off the Power Bus as much as you can. There's always exceptions, but that's a good place to start.

Strategically place resistors, diodes, caps, etc. so you can run traces in between the leads.

Don't hesitate to drag the pads to where you need them. Metal Bends! :tu:

Jumpers, Jumpers, Jumpers!!!

Leave yourself a little space while you're laying the circuit blocks out. You can pull them closer after you optimize their placement.

Don't be afraid to rip stuff up and move it around. That's what the SaveAs is for. :hihi:

User avatar
Tombola
Super Deluxe Wiggler
Posts: 1878
Joined: Sun Jan 23, 2011 11:33 am
Location: London, England

Post by Tombola » Wed Mar 14, 2012 10:49 am

ultrashock wrote:yes, that's some sort of art, definitely...
Image
That's awesome...

User avatar
hiawog
Ultra Wiggler
Posts: 892
Joined: Wed Jun 29, 2011 3:59 pm
Location: screwston tx

Post by hiawog » Wed Mar 14, 2012 11:10 am

this a really cool thread! i dont even do diy, but i understand enough to follow the conversation. mostly.

great tips folks.

User avatar
Rod Serling Fan Club
aquatic hitchhiker
Posts: 3760
Joined: Mon Dec 14, 2009 12:13 am
Location: MNTN

Post by Rod Serling Fan Club » Wed Mar 14, 2012 11:14 am

The few times I started to attempt PCB design I got discouraged quickly.

User avatar
J3RK
Super Deluxe Wiggler
Posts: 6613
Joined: Tue Dec 22, 2009 12:46 pm
Location: Seattle

Post by J3RK » Wed Mar 14, 2012 11:32 am

I run the autorouter a few times, just for reference purposes. If I can get an autoroute with no vias, then I know I have the components placed half-decently. (I place the components by hand based on their order/place in the schematic first.)

Once I have this non-via layout, I at least have a pretty good idea that it is at least possible to get a nice layout without too many/unnecessary layer transfers. I toss a ground-plane on the layer that has the most ground connections.

After that I start routing with the netlist visible. Unless I really need to squeeze something through a tight space, I always use T-30 traces or larger, and try to avoid righ-angles in the traces.

Once I have a half-decent layout, I start figuring out where I can cram bypass caps, beads, and other power conditioning components.

Works for me anyway. :goo:

frijitz
Super Deluxe Wiggler
Posts: 1637
Joined: Mon Aug 31, 2009 3:37 pm

Post by frijitz » Wed Mar 14, 2012 11:49 am

L-1 wrote:the secret is correct parts placement. I redraw with autorouter many times, move parts again and again, and play with autorouter settings to achieve good results.
That sounds effective as far as the simplest routing, but that isn't necessarily what you want. Considerations of ground loops, noise bypassing, etc really need to take precidence over neatness, IMO.

Ian

User avatar
Tombola
Super Deluxe Wiggler
Posts: 1878
Joined: Sun Jan 23, 2011 11:33 am
Location: London, England

Post by Tombola » Wed Mar 14, 2012 12:09 pm

frijitz wrote:Considerations of ground loops, noise bypassing, etc really need to take precidence over neatness, IMO.
I've been reading a few articles about PCB design (like this tutorial here: http://alternatezone.com/electronics/pcbdesign.htm ) and I've been quite surprised how much people talk about art and symmetry, and things 'looking wrong', and how little they talk about the actual electrical engineering involved.

Personally, I'll just be amazed if my thing sort of works without too many cludges and cut traces and IC legs poking out with bits soldered on...

User avatar
L-1
Super Deluxe Wiggler
Posts: 2171
Joined: Wed Dec 14, 2011 8:20 am
Location: Belarus
Contact:

Post by L-1 » Wed Mar 14, 2012 12:33 pm

Considerations of ground loops, noise bypassing, etc really need to take precidence over neatness
exactly yes.

User avatar
theabsent
?
Posts: 1472
Joined: Wed Aug 13, 2008 9:15 am
Location: Finland

Post by theabsent » Wed Mar 14, 2012 3:50 pm

I have once tried the autorouter. Since that I've drawn ~50 pcbs by hand : ) Some take longer than others but I'm pretty used to it already.
My releases: https://laitoshuoltaja.bandcamp.com/releases
My sound art & live gigs: https://www.facebook.com/Laitoshuoltaja/
Modular live gigs (our modular band): https://konekonekone.bandcamp.com/releases
Modular Patch of The Week Channel on YouTube: https://www.youtube.com/channel/UCTYqCy ... pvEmilJScg

Post Reply

Return to “Music Tech DIY”