Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 14 of 14

Thread: Teensy 3.1 Physical Width

  1. #1

    Teensy 3.1 Physical Width

    Hi All,

    I'm working on a very space-constrained project right now. Will I break anything if I file a Teensy 3.1 down to a width of 16.0 mm?

    The boards I have are 17.8 mm wide. I really need an extra millimetre of space. Two would be luxury.

    If I file the long edges of the boards down to the outside of the pins, I can drop that to 16.0. However, is the outside of the board used for anything? Do any traces run in that area that I will cut if I file it off?

    Thanks for any help.

  2. #2
    Senior Member
    Join Date
    Oct 2012
    Location
    Portland OR
    Posts
    706
    You could just start filing and see. If there is a trace you will see a bright copper stripe appear. Normally traces do not run right against the edge of a board, because that can cause trouble in manufacturing. However I have not tried this on a Teensy myself.
    Last edited by JBeale; 02-21-2015 at 11:10 PM.

  3. #3
    1.8 mm of 17.8 is almost 10% of the width that's to much I think...

  4. #4
    Senior Member
    Join Date
    Apr 2013
    Posts
    1,938
    If what you are trying to do is just take off half the width of the PCB holes so it looks like:
    https://forum.pjrc.com/threads/27826-SMT-Teensy-3-1

    then that shouldn't by itself kill the teensy unless Paul got really clever with the routing and went outside the holes somewhere. What will be a problem physically abuseing the board enough to achieve this. When they cut the boards during fab they are working without components so can clamp things in place and use guillotines and/or routers.

    PCBs are made from a variety of substrate but I'm guessing the Teensy's are fibreglass so actually physically cutting them is going to involve some serious effort and probably destroy the tool edge, and is also going to be a BAD THING done inside due to the dust produced. Second complication is that if you apply force to the through hole plating of the pin holes you run a good chance of lifting the track and destroying the connectivity, and optimal tools for cutting copper without applying force are not the same as those that will painlessly get through fibre glass. Clamping the board in place for this will also be interesting and probably require some sort of special jig to only apply force to bare PCB.

    So if you could magically make the material go away things would be probably be fine but the devil with this job is going to be in the details. And not killing yourself.

  5. #5
    Yes, exactly like that. Good pic, by the way.

    I am worried that Paul did route outside the holes, he's a clever kind of chap and I'd hate to trash a board by cutting a trace in that area, if there is one there.

    I'm thinking a file for relatively low force material removal, with the board held in rubber-faced jaws and the cutting force from front to back, i.e. so the back of the board is flush against the jaw. There will be dust, but if I prop up a vacuum cleaner with a HEPA filter running next to the vice then the dust is tolerably controlled.

    I'll give it a try tomorrow evening and see if I end up with a dead Teensy or not.

  6. #6
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    23,974
    Quote Originally Posted by happyinmotion View Post
    I am worried that Paul did route outside the holes, he's a clever kind of chap and I'd hate to trash a board by cutting a trace in that area, if there is one there.
    Well, here's a what the routing actually looks like on my screen:

    Name:  t3cad.jpg
Views: 237
Size:  10.8 KB

    As you can see, there are no trace routed outside the pads. Many of the traces to join to their pad horizontally in the center of the pad's horizontal axis, so if you sand all the way down to half the pad, you'll start to disconnect some pads from their traces.

    You can also see there's a good number of vias shortly after that half-pad line. You can also see the vias pretty easily by just looking at the board under a magnifier.

    The other feature that's not as obvious in that image is the green line near all 4 edges of the PCB. That's the boundary of the ground plane on layer 2 (Teensy 3.1 is a 4 layer PCB). You don't have to go very far in before you'll be sanding the edge of the ground plane. There's very little distance between the top layer and layer 2, but quite a lot between layers 2 and 3, so you'll want to make sure the sanding belt is traveling downward. Even then, you'll risk shorting the ground plane to anything else.

    Good luck, and I hope you'll post a followup with photos to let us know if this worked, or to serve as a caution for anyone else who might want to try.
    Last edited by PaulStoffregen; 02-22-2015 at 01:40 PM.

  7. #7
    Senior Member
    Join Date
    Jan 2015
    Location
    frisia
    Posts
    285
    You also might want to short all the pads before cutting, because the digital I/O pins lack the ESD protection diode. Either by putting conductive tape at the backside, or put a thin copper wire through all the hole, which goes from GND to Vin to 0 to AGND to 1, 3.3V, 2, 23, 3, 22, .... This pattern to make sure the wire stays on the inside.

  8. #8
    So I set about it with a coarse file and it was a piece of cake. Took it down to 15.9 mm wide.

    Click image for larger version. 

Name:	Teensy narrower 20150223_121401 - Copy.jpg 
Views:	117 
Size:	156.3 KB 
ID:	3603

    Holding it was a bugger, with the rubber jaws sitting on the USB socket and the reset switch. This doesn't appear to have caused harm, but I didn't tighten the vice up much. I also didn't learn on the file too hard to stop the board from slipping down in the vice.

    The only difficulty was breaking through the last bits of copper on the outside of each hole. As the copper gets filed to a thin film, the file just starts to push it downwards into the hole and the copper keeps bridging what should be a gap. Thus it looks like you are still filing the edge of each hole, even though you are actually cutting well past the edge. If you weren't paying attention, you could cut deeper than you needed.

    Click image for larger version. 

Name:	Teensy narrower copper bridging CM150223-11451801 - Copy.jpg 
Views:	111 
Size:	144.9 KB 
ID:	3604

    Anyway, I used a scalpel to cut the films and fold them over to the top, where the file could take them off.

    Click image for larger version. 

Name:	Teensy narrower messy edge CM150223-11481604 - Copy.jpg 
Views:	85 
Size:	200.3 KB 
ID:	3606

    The back edge of the board is a little messy, with a bit of lifting of the back rings. The file here is pushing the copper away from the board, so you could expect that. I tidied that up with scalpel and a fine file.

    I can just see ground plane on layer 2, but only the very edge. It's held in the board, so in no risk of shorting anywhere.

    Click image for larger version. 

Name:	Teensy narrower done CM150223-12131102 - Copy.jpg 
Views:	111 
Size:	136.5 KB 
ID:	3605

    Testing reveals that nothing is shorted to ground and the front of each pin is connected to the back. Obviously, I haven't tested all the functionality, but Blink still runs so we're good.

  9. #9
    Senior Member pictographer's Avatar
    Join Date
    May 2013
    Location
    San Jose, CA
    Posts
    700
    I was wondering if this would work. I hope you'll post pictures of the gadget that needs the skinny Teensy!

  10. #10
    It's for the next version of my glowstaff. I'm trying to squeeze far too much stuff into a one inch ID tube.

    Click image for larger version. 

Name:	Reese Dunn & Mitochondrion M4.2.3 at Spinfluence 2013 DSCF9241.jpg 
Views:	75 
Size:	116.8 KB 
ID:	3611

  11. #11
    Senior Member Jp3141's Avatar
    Join Date
    Nov 2012
    Posts
    486
    Those pads do have ESD protection (all pins on the IC do) -- it's just closer to a zener to ground than a diode to the supply.

  12. #12
    Senior Member pictographer's Avatar
    Join Date
    May 2013
    Location
    San Jose, CA
    Posts
    700
    Very nice! Thanks for the picture.

  13. #13
    Senior Member+ MichaelMeissner's Avatar
    Join Date
    Nov 2012
    Location
    Ayer Massachussetts
    Posts
    4,012
    Happyinmotion: I'm wondering out loud whether it might be less work to use a router to cut a hole on each side of your tube so that you can fit the Teensy in the tube, and have the ends overlap with the tube wall's, rather than trying to carefully whittle down the Teensy so it would fit inside, and you would not shear something off by accident. Or perhaps go to a slightly wider tube?

  14. #14
    I could, but two reasons not to:

    The tube is polycarbonate. Putting any holes or slots into it will create stress concentrators and do bad things to the toughness.

    The tube is already 25.4 mm inner diameter. I could go for a wider tube, but then it gets to be awkward to hold - glow staffs tend to be fatter already than fire staffs.

    Fitting in there alongside the Teensy are four LED strips, aluminium strips to hold the LED strips, a layer of shock absorbing and light diffusing foam, 12 Li-ion cells and a bunch of other crap. It all fits, just, but the Teensy is the widest single component hence my desire to slim it down.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •