Tactile switch help

Discussion in 'The Projects Forum' started by pbedford83, Nov 5, 2010.

  1. pbedford83

    Thread Starter New Member

    Nov 5, 2010
    5
    0
    Hello everyone,

    This is my first post here, and I need some advice before I do anything with an issue of mine.

    I have a laptop computer which I am modifying, part of the modification means relocating the power switch.

    After checking, the power switch is a small 4 terminal Tactile switch mounted to a PCB. the PCB can be removed and replaced easily, My question is:

    Would soldering wire to relocate the switch cause any detremental effects tot he switch or the PCB itself... As I cant find any other way around it as the laptop will be housed in a metal case..

    I Will insert an image below of the actual switch in question, the powwer switch is the far left switch.

    Thanks.

    Paul
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hi Paul,
    Welcome to AAC!

    I have no knowledge of your soldering skills. If they are not good, or particularly if you have never soldered before, then you need to practice quite a bit on some cheap or scrap/salvaged parts before you attempt it.

    If you don't have such things, Electronic Goldmine is an OK place to get some cheap parts to practice with.

    You also need to be aware of ESD, or electrostatic discharge. For you to even start to feel the effects of ESD takes around 3,000 volts. For you to hear a snap or pop during discharge, it takes around 10,000v. You can kill PC components with only 30v of static discharge.

    Low temperatures and low humidity make damage due to ESD very likely. High temps and high humidity make the chance of ESD much lower, but you should always wear an anti-static wrist strap, have an anti-static mat on your workbench, and connect them to earth ground.
     
  3. pbedford83

    Thread Starter New Member

    Nov 5, 2010
    5
    0
    Hi, thanks for the reply.

    I been building prijects for some time now, my soldering is quite good from what I can gather, although I have limited experience with these switches, ive never soldered one that was allready attatched to a PCB

    It was the heating up element that is an issue, although, I am going to by-pass the switch anyhow, and just use the terminals as a "jump off point", so although I will try and keep my soldering time down to just a second or two per terminal, if, worst case scenario, it did "pop" and die, the bye-pass would still take effect..... Right?

    Thanks
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, those tactile switches are fairly rugged, but your iron is going to need to be pretty warm to heat just the junction up quickly; if you're heating it for >3 seconds, you may damage/destroy it.

    The lead-free solder they're using nowadays has a higher melting point than the good old 63/37 and 60/40 tin/lead solder.
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    It is most likely a single pole, normally open momentary switch. There should be continuity between the two legs close to each other on each side (upper left and lower left, upper right and lower right). It should be open between the left side and right side until the button is pressed.

    If this is the case, you could parallel another momentary SPST NO switch off of the existing switch without removing it. Provided leaving it it the current position would be acceptable (different cover over it so it wouldn't be depressed).

    The switch sub-PCBs may be multilayer, so soldering and desoldering could be an issue. If you can see light through from one side to the traces on the other, it is a dual layer board. If you can't, then their is probably at least a ground plane between the two visible sides. This increases the difficulty of soldering a wire into a hole where a pin was removed.
     
  6. pbedford83

    Thread Starter New Member

    Nov 5, 2010
    5
    0
    I'll probably leave the current switch in place and just add another in a different location, instead of trying to remove it.
    I know it's elementary but the other thing that's worrying me is getting the correct points in which to solder, if I leave then switch there then from what "thatoneguy" just explained, the points to solder would be one from left to right side on the points closest together, say from the picture, if I soldered the switch from top left to top right, would I then need to wire the other two points together to make continuity, as I was planing on using a 2 terminal NO switch. Just looking at making the least amount of solders possible...

    Thanks
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Some may be DPST, upper left and upper right are one circuit, and lower left and lower right are another.

    This is where measuring with an ohmmeter becomes important before doing anything to it. Disconnect the ribbon wire where it leads to the motherboard so you know you are measuring only the switch in question to verify it is what you think it is.

    Worse case is having to run 4 wires. These would need to be small gauge, and if going for any distance, twisted pair or other shielding.
     
  8. pbedford83

    Thread Starter New Member

    Nov 5, 2010
    5
    0
    Ah, yes, tha makes much sense.

    So fingers crossed ill only get continuity between two points when pressed and not all 4.

    Worst case scenario ill just use a 4 terminal switch.

    Thanks a lot for your help.
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Actually, you should get continuity between all 4 when the button is pressed.

    The part is making sure the 2 sides are each a pole, rather than the 2 pins on each side being a pole, making it a DPST Momentary.

    The pins on the left side should be connected/0Ω whether the button is pushed or not. Same with the right. This means that all 4 would be connected when pressed. If it is different than this, post your results, both button up and button pressed.
     
  10. pbedford83

    Thread Starter New Member

    Nov 5, 2010
    5
    0
    I will, thanks for your help, I'll upload my findings and a pic when I'm done.

    Fingers crossed.
     
Loading...