911!!! Need to figure out how to debounce my switch

Discussion in 'The Projects Forum' started by MATTY B, May 18, 2008.

  1. SgtWookie

    Expert

    Jul 17, 2007
    22,201
    1,809
    OK, what voltage are you measuring at pins 1 & 2 without pushing the start button? You should be getting at least 10v. If not, the cap may have too much leakage current; try unsoldering the cap and measure again.

    If it's still below 10v, replace the 220k R2 with a 100k resistor, and the new 1uF cap with a 2.2uF cap. This keeps the 0.2 second debouncing delay, but allows more current flow to the input of the IC.

    How long did you have the soldering iron on the pins when you were shorting them out? You may have overheated the IC.
     
    Last edited: May 20, 2008
  2. MATTY B

    Thread Starter Active Member

    Jan 26, 2008
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    0
    I pulled the board out of the car and hooked to a 9 volt supply. If it wont work at 9 volts thats no good cause its easily possible to drop below that during cranking if the battery is low. I barely touched the IC when I shorted them, I just balled up a good drop of solder on the iron and blobbed it over so it was probably on it for maybe a second at most. I ended up putting it back to the way it was and ordered a switch overnight UPS so thats all I can do. Now heres a question, is there a way to make any kind of daughter board I can make that will provide a clean signal to the module utilizing a momentary switch? It would be very easy for me to do that if there was a secondary circuit I can just wire into the no,nc and com pads on the board. If I can do that then Im in buisness if not then oh well just gotta deal with it.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,201
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    OK, so is it working as it was before, when you just momentarily short across NC and NO?
     
  4. MATTY B

    Thread Starter Active Member

    Jan 26, 2008
    45
    0
    yep works the same as it did. I can touch the no and nc alternatley to com and it will step but when hooked up through the relay to do the switch I get erratic jumps. So the board is fine in the sense that its not damaged from modifying it, back to the new question is there a circuit i can build for the switching portion prior to getting to the main board? Maybe something that replicates a spdt switch in its outputs but is able to work with a momentary switch for function? I have found many circuits on debouncing a switch itself but nothing about switching like an SPDT. If you have any leads or ideas about this as a possible solution it would save me alot of trouble of modifying the main board and I could just hook it in between.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,201
    1,809
    OK, here's an add-on board. I'm not extremely happy with it, but it should do the job for a while, anyway.

    On the left of the schematic is just a portion of Soren's board, showing a representation of the NC, NO, and COM connections. You'll need to add a connection somewhere between R2 and R3 to supply power to the add-on board.

    S1 is shown as a SPDT toggle switch, but that's just because it's easier for me to run simulations. Just assume it's a SPST NO pushbutton.

    C2 is just a small electrolytic for supply filtering. It should be roughly 3x-8x the size of C1.

    C1 and R6 control the toggle time when switch S1 is pushed. C1 and R4 control the toggle time when switch S1 is released. U1 is a quad NAND Schmitt trigger. I could've used a 40106, but you know that you can get 4093's, and you might have an extra.

    If the time needs to be longer, increase C1 slightly. Right now, response time for pushing the button down is around 60mS and response time for releasing the button is around 200mS.

    Note that power/ground connections to U1 are not shown. Vdd should be connected to the point that says Dvdd.

    U1C and U1D are spare gates. They must have their inputs connected to either ground or Vdd to prevent unwanted oscillations.
     
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