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Logic DPST using a SPST switch?

Discussion in 'Datasheets, Manuals or Parts' started by slow_rider, May 20, 2009.

  1. slow_rider

    slow_rider New Member

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    there isn't really a problem as for width and length available, only height. I actually did a drawing of the box is SolidWorks and everything will fit inside nicely. There's about 17mm height where the relays should be placed.
     
  2. KMoffett

    KMoffett Well-Known Member

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    So you have lots of room for any size of battery as long as one dimension is less than 17mm? How about posting the drawing here.

    ken
     
    Last edited: May 22, 2009
  3. slow_rider

    slow_rider New Member

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    [​IMG]

    The 9V battery will be under the PCB, on top of the PCB there is room for various electronics.
     
    Last edited: May 22, 2009
  4. dave

    Dave New Member

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  5. KMoffett

    KMoffett Well-Known Member

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    I am truly stumped. I can't think of a simple circuit that when powered-up will switch the relay, power-down, and remember what it did the last time so it will do the opposite the next power-up...all with an SPST push button.

    ...........Except an microcontroller. :) I've used a PICAXE 8M to power-up with an SPST pushbutton, perform a task, store a variable in non-volatile memory, and kill its own power.

    How exotic are you willing to go? 8-pin PICAXEs are about $3.50, have a free BASIC programming editor, and require only a 3-wire serial cable and two resistors to program. (Since most newer computers don't have a serial port, you may need a USB-to-Serial adaptor. :( ) Switching will not be instantaneous...fraction of a second...if that's a problem.

    Ken
     
  6. slow_rider

    slow_rider New Member

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    I think a MC is a little too much for me right now... :)

    The FF will save it's status when not getting any power, right? If so, I can use a JK-FF that will get a signal clock together with signals to both inputs (same signal) and it will cause to flip mode. The only thing is that the inputs need to be set before the clock signal starts to drop, so if I could delay the path to the clock input by a really short time I think this could work?
     
  7. KMoffett

    KMoffett Well-Known Member

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    No. Thus the problem. :(

    Ken
     
  8. slow_rider

    slow_rider New Member

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    Maybe it would be possible to lower the current draw to a minimum while the switch is not pressed?
     
  9. KMoffett

    KMoffett Well-Known Member

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    Can your audio signal tolerate an insertion resistance of 80Ω? Like sticking an 80Ω resistor in series with the audio line. A relay has a 0Ω insertion resistance. I'm thinking of a circuit with an analog switch IC instead of a relay. The quescent current draw with the circuit always on is about 20µA. With a 9v alkaline battery at 500mAh, the circuit would probably run for two years.

    ken
     
    Last edited: May 24, 2009
  10. KMoffett

    KMoffett Well-Known Member

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    Something like this.

    Ken
     

    Attached Files:

  11. slow_rider

    slow_rider New Member

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    The logic switches are actually switching FETs, right? If so that would change the impedance of the incoming signal even when bypassed, no?
     
  12. KMoffett

    KMoffett Well-Known Member

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    The FETs will appear open when off, and as an ~80Ω series resistance when on. This will appear to add 80Ω to you source impedance. Depending on your audio circuit, which you haven't defined, this may or may not be significant.

    Ken
     
    Last edited: May 26, 2009
  13. slow_rider

    slow_rider New Member

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    I ordered some parts and I'll try to build the the first circuit you posted. By the way, do you think a diode could be replaced by an LED for indication when the circuit is open and when closed?
     
  14. KMoffett

    KMoffett Well-Known Member

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    I assume that you're referring to the one-coil relay circuit. The diodes (4) are all there for the protection of the IC from counter EMF spikes as the relay switches polarity. You could add a resistor and LED in series, and place that across the relay coil. LED-on indicates one state, LED-off indicates the other state. But remember, this adds to the continuous currant drain on your battery. And that circuit doesn't really take advantage of the relay's latching function.

    Ken
     

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