DPDT make-break switch that cycles at least 10 times per second.

Discussion in 'The Projects Forum' started by Ashanti, Nov 22, 2008.

  1. Ashanti

    Thread Starter Member

    Nov 22, 2008
    12
    0
    I am a musician experimenting with a sound effect. I need a dpdt switch that continually switches between two effects. I get the sound I like using a dpdt manual switch but I need to have the switch continually move between the two sources. I've read about an "h-Switch" but have been unable to find one that continually switches. I want to be able to adjust the rate of the switch from 2 times per second upto 100 times per second. Is there one for sale or should I build one. Finally, I need it switch to work using a 9 volt battery. Help me Obie Wan. You're my only hope.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    If you're using line-level audio signals, you might use an analog switch like a CD4066B controlled by a 555 timer in astable mode. No moving parts like a relay.
    [eta] A Dallas/Maxim MAX303 has a much lower ON resistance than a CD4066B, and would be easier to use in your application.
     
    Last edited: Nov 22, 2008
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    I would say that you are going to need a electronic part called a analog switch. Something like this - www.fairchildsemi.com/ds/FS/FSA2467.pdf. Mechanical switches probably will not be satisfactory due to contact bounce and log pull in and release times.

    Dealing with packages can be a challenge. You may need to find something in a DIP package.

    Also, you can get the same action with single pole switched, but use several for each channel switched. You might be able to use tha CMOS CD4066, for instance.

    In all cases, a LM555 timer can be the source of the switching signal. The switching frequency can also be changed while it operates.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    See the attached schematic for one possible solution.

    I checked prices on the MAX303; they're getting pricey nowadays (around $10/ea). The CD4066's are available for under $0.50/ea.

    The ICM7555 is a CMOS version of the ubiquitous 555 timer. It consumes less power than it's bjt cousin, and it's output on pin 3 is nearly rail to rail.

    Not shown in the schematic are bypass capacitors on the IC's power connections. Use a 100nF on the 4066 and the ICM7555, and an additional 10uF cap on the ICM7555.

    The 22k resistors are to reduce the possibility of "popping" due to capacitance on the inputs/outputs.

    The 2N7000 N-ch MOSFET is used as an inverter.

    X1 and X2 are the "common" RCA jacks.
    X1 is alternately connected to X3 or X4.
    X2 is alternately connected to X5 or X6.
    R1 and R2 control the high-side and low-side pulsewidths, therefore the frequency of switching. R3 limits the maximum frequency, and helps prevent overloading the output.
     
  5. Ashanti

    Thread Starter Member

    Nov 22, 2008
    12
    0
    Thank you very much
     
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