I designed a PCB. What''s wrong with it? Trace Width calculator
Archiver
Posts: 46,084
> >> R-1 is located so as to force pins 4,5,6 and 7 to angle on exit.
> R-1 only needs to be 1/4 watt or even 1/8 watt so the traces are
much
> larger than required. <<
>
> I thought that R1 would be in the neighborhood of 2 watts, as it
> serves as the global current limiter for all of the LEDs (20ma * 18
> segments * 5v=1.8 watts), so I was being generous with the traces.
Of
> course, I make the assumption that it has to be able to handle all
the
> current going through the LEDs.
Assuming 5 volts, with 18 segments of LED's at 20mA each is 360mA or
say, 0.5amps.
Check out this link.
http://www.geocities.com/CapeCanaveral/Lab/9643/TraceWidth.htm
and put in 1/2 ounce copper instead of the 2ounce default. (it will
make the traces larger)
> In general terms, I tried to scale the trace widths to the current
> flowing through it. Signals given the smallest traces. Major +5 and
> GND feeds given the largest.
As you will find with that link, your traces for the LED's are way
oversized per the requirements. I like larger traces for another
reason. I can lay a wire on a trace to make a post cutting
correction.
>
> >> Also, since you have 3 resistors for each LED, I would group the
> resistors in lots of 3. Running them around the mounting hole is no
> biggie, but for troubleshooting it is much easier if the layout is
of
> components aligns with the devices they serve. <<
>
> I thought about that. With my limited knowledge, I figured that the
> bigger problem would be drilling the holes. So I kept as many as
> possible in a straight line to make that part easier. With my intent
> in mind, was that a good decision or a bad one?
Drilling holes is a tricky business. I would recomend getting a few
MACHINED chip sockets and drilling out all the pins. Get a couple
drills. Then uisng a magnifying glass and a pin, create a depression
in pin one of the DIP. that would help to align the drill in the
center of the pad.
Place the drilled out socket on the board and use a spare drill bit
to align the holes. Line up the opposite corner and drill that
hole. Pin it with a drill bit and then drill what holes are left as
you can.
For a first time board, I would highly recomend you use larger traces
and don't try to run traces between pads if at all possible.
If you do toner transfer, considder making the two pads and trace as
one spot and using an exacto knife to scrape off toner. You can get
some fine etched lines that way.
Also, if you have the opportunity, use larger pads. Drilling small
pads can rip pads from the board.
Dave
> R-1 only needs to be 1/4 watt or even 1/8 watt so the traces are
much
> larger than required. <<
>
> I thought that R1 would be in the neighborhood of 2 watts, as it
> serves as the global current limiter for all of the LEDs (20ma * 18
> segments * 5v=1.8 watts), so I was being generous with the traces.
Of
> course, I make the assumption that it has to be able to handle all
the
> current going through the LEDs.
Assuming 5 volts, with 18 segments of LED's at 20mA each is 360mA or
say, 0.5amps.
Check out this link.
http://www.geocities.com/CapeCanaveral/Lab/9643/TraceWidth.htm
and put in 1/2 ounce copper instead of the 2ounce default. (it will
make the traces larger)
> In general terms, I tried to scale the trace widths to the current
> flowing through it. Signals given the smallest traces. Major +5 and
> GND feeds given the largest.
As you will find with that link, your traces for the LED's are way
oversized per the requirements. I like larger traces for another
reason. I can lay a wire on a trace to make a post cutting
correction.
>
> >> Also, since you have 3 resistors for each LED, I would group the
> resistors in lots of 3. Running them around the mounting hole is no
> biggie, but for troubleshooting it is much easier if the layout is
of
> components aligns with the devices they serve. <<
>
> I thought about that. With my limited knowledge, I figured that the
> bigger problem would be drilling the holes. So I kept as many as
> possible in a straight line to make that part easier. With my intent
> in mind, was that a good decision or a bad one?
Drilling holes is a tricky business. I would recomend getting a few
MACHINED chip sockets and drilling out all the pins. Get a couple
drills. Then uisng a magnifying glass and a pin, create a depression
in pin one of the DIP. that would help to align the drill in the
center of the pad.
Place the drilled out socket on the board and use a spare drill bit
to align the holes. Line up the opposite corner and drill that
hole. Pin it with a drill bit and then drill what holes are left as
you can.
For a first time board, I would highly recomend you use larger traces
and don't try to run traces between pads if at all possible.
If you do toner transfer, considder making the two pads and trace as
one spot and using an exacto knife to scrape off toner. You can get
some fine etched lines that way.
Also, if you have the opportunity, use larger pads. Drilling small
pads can rip pads from the board.
Dave