Shop OBEX P1 Docs P2 Docs Learn Events
Quickstart freezes when held in hand: Fixed with tape on bottom — Parallax Forums

Quickstart freezes when held in hand: Fixed with tape on bottom

RaymanRayman Posts: 14,670
edited 2012-11-04 06:52 in Propeller 1
I was just testing out RamPage2 this morning with a Quickstart and noticed that my Quickstart would sieze up if my fingers touched something on the bottom of the board... It didn't reboot, it seemed to freeze.

So, I did a bit of playing around and I think it's touching the XI and XO holes under the crystal that are the most susceptible.
Also, touching around the XI pin on the 40-pin header will do it too, but you have to try harder.

Anyway, I decided to put tape on the bottom of the board, over the crystal and the 40-pin header.
This prevents it from freezing. Just a little worried that the PLL might die without this...

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2012-11-03 08:56
    That's no surprise. The crystal oscillator is a high impedance circuit and skin resistance is enough to short circuit it in addition to coupling of 60Hz noise via skin resistance / capacitance. You'd have a similar effect on I/O pins if you touched that area and you had a program that copied the state of input pins to LEDs. The PLL seems most sensitive to currents across the chip when not all Vss / Vdd pins are used or they're inadequately bypassed.
  • RaymanRayman Posts: 14,670
    edited 2012-11-03 10:16
    It took me few minutes to figure out what was going on... Of course, it's relatively obvious what was happening in retrospect.

    Frankly, I think exposing the crystal inputs like that is a bad design decision. I'm not really sure what benefit it has at all...
    To use a different crystal you have to unsolder a resistor from the board. Why not just unsolder the crystal?
    And, why have XI on the 40-pin header? I think that would only very rarely be desired...

    But, I don't think it really matters too much, unless this is happening to a lot of people besides me...
    Or, if this is actually damages the Prop's PLL. It does freeze up, but maybe not really doing damage...
  • MagIO2MagIO2 Posts: 2,243
    edited 2012-11-03 10:55
    I covered my quickstart with masking foil which is used by airbrushers. One piece covering top and one covering bottom side. The holes for screws, connectors and buttons can easily be cut out with a cutter.

    It simply makes the quickstart a little bit more workshop friendly (with wires llying around ;o)
    1351964719-picsay.jpg
    346 x 233 - 23K
  • jmgjmg Posts: 15,173
    edited 2012-11-03 14:17
    MagIO2 wrote: »
    I covered my quickstart with masking foil which is used by airbrushers.

    Nicely done, how thick is that ?
  • MagIO2MagIO2 Posts: 2,243
    edited 2012-11-03 15:41
    The foil is 1/2 mm thick.
  • frank freedmanfrank freedman Posts: 1,983
    edited 2012-11-03 19:00
    Maybe paint the bottom with conformal if you can get it, or give the bottom a coat of corona dope from any reputable TV repair supplier.....
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2012-11-04 06:38
    I like using the 2" wide clear plastic packing tape. I use 2 layers.

    Caution!! All tape can produce static charges when pealing from the role.
    To discharge this charge "Breath Heavily" on the glue to deposit a film
    of moisture before applying to the board.

    Packing tape is quite robust especially with 2 layers.

    The "best" tape to us is that brown colored "Kapton" tape as its very tough
    to mechanically puncture. A bit expensive though.

    Duane J
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2012-11-04 06:52
    I usually use Scotch 2228 Rubber Mastic Electrical Tape. It is thick and provides a nice insulator on PCBs. You can get it at Home Depot.
Sign In or Register to comment.