1
\$\begingroup\$

maybe trial and error is the only solution here I'm trying to build a custom eagle part for board placement. This is the first part I've built. I've got the pins properly placed, but I'm trying to get an outline of the entire component. Here is the schematic from the MFG:

LED 3 Digit

The problem is. I don't know how to place pin one properly. I've done an outline that's close to the nearest grid point. Is that as good as it's gonna get? This is what I have so far. Any tips/advice would help out a lot. Thanks!

LED so far

\$\endgroup\$
2
\$\begingroup\$

The pin array is exactly centered on the LED module outline.

So pin 1 is 0.3" below center and 0.25" left of center.

Give yourself a bit of room, there will be a bit of slop in your holes, and the pins will not be exactly straight when the clear epoxy is poured into the mold.The width is 1.48" nominally, so (assuming you're using an imperial grid) you could use 1.50".

Place the pins in their exact positions first and place the outline later, and you can make it a bit bigger than the nominal size of the part.

In this case, I might put the center of the part on pin 1 or at the exact center of the part.

\$\endgroup\$
2
\$\begingroup\$

No, the closest grid position is not automatically good enough for pins or other features. The fundamental realization should be that you don't have to place features on the existing grid.

  • You can temporarily change the grid to something that works for the needed features

  • You can individually select the features and edit their actual coordinates to the correct location irrespective of the grid

Also note that you can temporarily switch the units between inches and mm to fit whatever your documentation is in.

Finally, if doing PCB design you really should have the part and a cheap pair of digital calipers in hand for double checking. If you doubt the result, print it out at 100% scale (put a known diameter box around it which you can measure to verify the printer scaling) and set the part on the paper.

In your specific case, the pins of the part will fit on a 100 mil / 2.54 mm grid, however the housing outline may not. In that case you'd probably be happiest leaving the pins on grid, and adjusting coordinates of the outline corners numerically

It's also worth noting that you've used square pads for all pins. Where practically workable, it's something of a tradition to use a square pad for pin 1 and round pads for the others, so that they may be readily distinguished without reference to silkscreen.

\$\endgroup\$
  • 1
    \$\begingroup\$ It is useful to remember that the component outline location is not highly critical - the CAD program doesn't care about it - it only serves as a guide for you when placing the component, and other components around it. I think I often made the outline a little larger than the component, if that made the corners align with convenient grid points. \$\endgroup\$ – Peter Bennett Jul 14 '18 at 23:39
  • \$\begingroup\$ If you're just slapping something together, perhaps. But boards are often designed to fairly tight mechanical limits, too. And there's increasing effort to 3d modeling the board and test-fitting it in a 3d model of the housing to avoid nasty surprises when the first prototypes of each come back and an attempt is made to assemble them... \$\endgroup\$ – Chris Stratton Jul 15 '18 at 6:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.