Homebrew PCBs

I am trying to build a PCB layout. I have very limited experience 
even making schematics. I have mostly worked by breadboarding 
circuits, adjusting until it works, then using point-to-point 
wiring. Or, I have worked with prebuilt PCB's.

So, this is a learning experience for me. This time, I breadboarded 
a circuit, and then I created a schematic. The next step is to see 
how I would make a PCB from this.

I used ExpressSCH (from ExpressPCB.com) to create the schematic. I 
am fairly pleased with the results.

Questions:

- The software recommends linking a schematic to the PCB. Why is 
this important?
- Should "good" PCB software take the schematic output and begin the 
PCB layout for you? It seems that the software should at least place 
all the components onto the PCB in a rough manner for you. Does 
anyone know if this software does this?
- Does Eagle SW make it easier to do any of these tasks?
- Does anyone know of a library for Eagle that includes the 
PIC16F7*7 devices?

Thanks in advance,

Bob H.

--- In Homebrew_PCBs@yahoogroups.com, "Bob Hyland, PMP" 
<BobHyland@A...> wrote:
>
<snip>
> - The software recommends linking a schematic to the PCB. Why is 
> this important?

Unless your circuit is extremely simple, connecting the pads in the 
PCB layout is going to be difficult and error-prone. Also, any 
changes that need to be made to the circuit can be done much more 
easily on the schematic and then transferred to the PCB.


> - Should "good" PCB software take the schematic output and begin 
the 
> PCB layout for you? It seems that the software should at least 
place 
> all the components onto the PCB in a rough manner for you. Does 
> anyone know if this software does this?

While most (all?) CAD packages have some sort of an auto-place 
feature, it's generally of very limited use. Most of them seem to 
randomly scatter the parts onto the board with no regard to their 
interconnections. IMO, parts placement is something much better done 
by hand. Doing so lets you use the rats-nest of the nets as a guide 
to get a good arrangement for the parts.


> - Does Eagle SW make it easier to do any of these tasks?

Yes. A lot of people use Eagle. Their freeware version is probably 
one of the most popular packages among hobbyists.


> - Does anyone know of a library for Eagle that includes the 
> PIC16F7*7 devices?

I'm sure that someone in the group who uses Eagle has one.


Regards, Bob

--- In Homebrew_PCBs@yahoogroups.com, "Bob Hyland, PMP" <BobHyland@A.
..> wrote:
>Does anyone know of a library for Eagle that includes the PIC16F7*7 
>devices?

Hey Bob,

Lately, I've just gotten in the habit of grabbing the generic DIL 
packages from the "ic-package" library in whatever pin config. that I 
need and making my own connections to that. I'll also use pin headers, 
sockets, or anything else that has the right footprint and pin 
spacing. You can also tie pins to ground planes or supply lines, or 
copy/rename library items and customize them graphically or designate 
the pins. Be warned- The create new item features in Eagle are useful 
and necessary, but extremely WEIRD and maybe not so intuitive (as are 
some of the group and copy functions). It's a wonderful program, but 
it may have been written by aliens (I know the manual was).

I also haven't been using the schematic much lately, but it would be 
useful as a circuit reference for anything complicated. I've been 
adding all my chips in the board app, then connecting all the wires, 
then dragging them all over the blank area around the board and 
rearranging or rotating them until I have the least amount of criss-
crossed lines. Then I move them into the board area and start trying 
to route. You usually still have to move some after that. You can also 
easily rotate with the right mouse button, while you're using the move 
tool. Unless I'm doing something wrong, moving them after you've got 
route lines happening can get really messy. It will keep the original 
lines and turns, and let them cross over themselves, add segments to 
them,etc. I usually rip up the routes beforehand for anything that 
needs moving.

                         Good Luck,
George

PS- There's a user library folder somewhere in the ftp at Cadsoft 
(maybe in user or pub). Could have your PIC, or another one with the 
same pinnings (Microchip usually has a few similar ones).

I'm closer to the opposite extreme than Bob. It's useful to model the 
individual gates so the schematics somewhat reflect the intended design. For 
example, each transistor in a dual MOSFET is drawn as a transistor, not 
abstract pin numbers in box. I'm often unaware of actual pin numbers and 
function even during board layout.

Full agreement here that Eagle's interface is quite different from any other 
application. The "alien" nature is very likely due to its origins in East 
Germany (I think.)

I also echo Bob's sentiment to learn the library functions quickly. As often 
as not, each new board adds a few new chips or packages to the library. PICs 
are a special case. It's pretty straightforward to draw the new chip, more 
so than stretching an existing one and renumbering pins. I sometimes think I 
want to add symbols inside the block to indicate pin function -- e.g.: 
comparator or A/D -- but never actually get around to doing so. Even if I 
did, the configuration will be different on the next board even if it was 
the same chip. (It sure would be nice to modify one of the those graphical 
PIC configurator programs to spit out a custom Eagle symbol along with 
configuration code. I don't expect I'll ever get around to that either.)

----- Original Message ----- 

From: "soffee83" <soffee83@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Monday, January 16, 2006 2:07 PM
Subject: [Homebrew_PCBs] Re: Help with a PCB layout


> --- In Homebrew_PCBs@yahoogroups.com, "Bob Hyland, PMP" <BobHyland@A.
> ..> wrote:
>>Does anyone know of a library for Eagle that includes the PIC16F7*7
>>devices?
>
> Hey Bob,
>
> Lately, I've just gotten in the habit of grabbing the generic DIL
> packages from the "ic-package" library in whatever pin config. that I
> need and making my own connections to that. I'll also use pin headers,
> sockets, or anything else that has the right footprint and pin
> spacing. You can also tie pins to ground planes or supply lines, or
> copy/rename library items and customize them graphically or designate
> the pins. Be warned- The create new item features in Eagle are useful
> and necessary, but extremely WEIRD and maybe not so intuitive (as are
> some of the group and copy functions). It's a wonderful program, but
> it may have been written by aliens (I know the manual was).
>
> I also haven't been using the schematic much lately, but it would be
> useful as a circuit reference for anything complicated. I've been
> adding all my chips in the board app, then connecting all the wires,
> then dragging them all over the blank area around the board and
> rearranging or rotating them until I have the least amount of criss-
> crossed lines. Then I move them into the board area and start trying
> to route. You usually still have to move some after that. You can also
> easily rotate with the right mouse button, while you're using the move
> tool. Unless I'm doing something wrong, moving them after you've got
> route lines happening can get really messy. It will keep the original
> lines and turns, and let them cross over themselves, add segments to
> them,etc. I usually rip up the routes beforehand for anything that
> needs moving.
>
>                         Good Luck,
> George
>
> PS- There's a user library folder somewhere in the ftp at Cadsoft
> (maybe in user or pub). Could have your PIC, or another one with the
> same pinnings (Microchip usually has a few similar ones).
>
>
>
>
>
>
>
> Be sure to visit the group home and check for new Links, Files, and 
> Photos:
> http://groups.yahoo.com/group/Homebrew_PCBs
>
> If Files or Photos are running short of space, post them here:
> http://groups.yahoo.com/group/Homebrew_PCBs_Archives/
> Yahoo! Groups Links
>
>
>
>
>
>