On Sat, 9 Jul 2011 05:19:01 -0600
Ed Hartnett edwardjameshartn...@gmail.com wrote:
On Mon, Jul 4, 2011 at 7:46 AM, DJ Delorie d...@delorie.com wrote:
I am trying to make my first PCB and I have selected a
super-simple
circuit
to start with, a 555 astable circuit. It's a single-sided board,
and I'm going to etch it myself - something I've always wanted to
try.
But what footprints do I use for the GND and VCC connections? I
guess I would just like these to be two pads on the PCB. Is there
a way to tell gschem this? Or do I just manually make that change
in the pcb program?
Usually, you would add one two-pin connector, or two one-pin
connectors, for the power connection. There are a range of
footprints available for this - if you just want to solder wires to
it, HEADER2_1 is sufficient - it's just two pins on 0.1 centers.
Would this be done in gschem? Or in pcb?
In gschem I have a symbol for gnd, and there is no footprint
associated with it. There is another symbol for +5 V. Do I add a
connector on gschem and use it instead of then GND/5V symbols? Or do
I associate a footprint of HEADER2_1 with each of them? Or with one
of them?
I think Kai-Martin probably answered this pretty thoroughly, but I'll
comment that, like you, I once wanted to add two plain old surface mount
pads to which I could solder my power/ground supply wires.
You correctly noted that GND/+5V symbols don't have a footprint
associated. These “power rail” symbols, like the input/output pin
symbols (input-2.sym, etc.), are schematic conveniences only. You
could remove them and instead connect all nodes with actual net lines
instead, but that is often very messy. The power rail and I/O pin
make schematics cleaner.
What you want is to use is either
(1) use connector2-1.sym, and then assign it a 2-pin footprint like
“JUMPER2” (2-pin SIP, 100 mil pitch through-hole header). Then connect
pin 1 of the connector to your ground net and pin 2 to your power net
(or vice-versa). If you want surface-mount pads, you can assign the
connector component a 2-pin SMD footprint like “RESC4532M”.
or if you want to be able to separately place the power and ground
connections on the PCB layout:
(2) insert two one-pin symbols (e.g., terminal-1.sym connector1-2.sym,
but note that these are “heavy” symbols and you need to change the
footprint unless you want the default though-hole pin footprint).
Connect one symbol to your ground net and one to your power rail net.
Assign the appropriate footprint--for a through-hole footprint, use
“JUMPER1”, “CONNECTOR 1 1”, or “SIP1N”; for a surface-mount footprint,
use a test-pad symbol or other single-pad SMD footprint (look on
gedasymbols.org; AFAIK the default pcb footprint library doesn't have
any single-pad SMD footprints).
Tip: If you use a 2-pin through-hole JUMPER2 footprint, you can solder
a 2-pin header from a ubiquitous single-row breakaway header (100 mil)
and then have a detachable power supply connection. I have found the
low-cost Molex KK-100 series kit (see [1] below) invaluable for all
sorts of connections like this. With a bit of practice, you will be
able to quickly made a wide variety of cables from 1 to 10+ pins. I
use bits of ribbon cable to make most signal connectors because it's
very convenient and looks tidy when you're done.
Regards,
Colin
References
[1] Molex KK-100 Connector Kit
With premium crimp tool (I highly recommend this option):
Molex Part #: 76650-0009
Mouser link:
http://www.mouser.com/ProductDetail/Molex/76650-0009/?qs=sGAEpiMZZMtsLRyDR9nM1%2ffCLkgKsWdRr36mItq8jVo%3d
With basic crimp tool:
Molex Part #: 76650-0007
Mouser link:
http://www.mouser.com/ProductDetail/Molex/76650-0007/?qs=sGAEpiMZZMtsLRyDR9nM1%2ffCLkgKsWdRSyrCqTUdKBE%3d
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