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Long input activated circuit

Discussion in 'General Electronics Discussion' started by Yllis, May 1, 2018.

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  1. Yllis

    Yllis

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    May 1, 2018
    I've built a voice operated switch for a clay pigeon thrower. It consists of a microphone, amplifier, bar display driver and a transistor that activates the thrower when a high enough volume is detected by the microphone. The idea is that the shooter could vocally activate the thrower.
    Now the problem is that the thrower is also activated by other loud noices like the muzzle blasts and reloading of the used shotgun.
    I thought I could change the circuit so that it would only be activated when the loud enough sound has lasted over a certain period of time. This way the sharp, short loud noices like the muzzle blasts would be filtered away.

    So how to make a circuit that is only activated when it's input has lasted over a certain period of time?
     
  2. WHONOES

    WHONOES

    856
    206
    May 20, 2017
    You could use the output of your circuit to trigger a timer and then logically and them together then if the sound is still present when the timer terminates, the system will trigger.
     
  3. AnalogKid

    AnalogKid

    2,349
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    Jun 10, 2015
    The timer part is called a monostable. The flow goes like this:
    Voice detector circuit determines that a sound is loud enough.
    Loud sound triggers monostable timer
    At the end of the time period, a logic circuit looks at the output of the voice circuit.
    If the voice circuit still is "true", the logic circuit activates the thrower.

    Since you already have the voice circuit, what is needed is the monostable and gating. All of this fits in a single CD4093 quad NAND gate package.

    What is your power source?
    What is the amplitude of the signal out of the voice circuit that activates the thrower?
    What is the thrower driver transistor part number?

    ak
     
  4. WHONOES

    WHONOES

    856
    206
    May 20, 2017
    Yup. You could use a 555 for the timer. Or you could do the whole lot with a bunch of Schmitt nand gates as in the 4093 that AK recommends.
     
  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    For the logic, the signal state that triggers the timer has to be in the same state when the timer cycle ends. A standard 555 "monostable" cannot do this because if the trigger input still is low the output does not change state, and if the trigger signal is differentiated to solve that problem, it might have returned to the non-voice state and the timer will keep going. Plus, you still need some kind of combinatorial something to evaluate the states of the timer and trigger signals and determine whether or not to activate the thrower.

    Retriggerable monostable (actually, a pulse stretcher)
    AND/NAND gate function
    Output transistor

    One CD4093 plus one diode can do all of it.
    OR, one ULN2004 darlington array (mo go-to part for stuff like this)
    OR, nothing but 2N7000 FETs (about 4 of them.

    BUT, thinking this through, you might not need any output gating. The voice circuit and the retriggerable might be all that is needed. 2 small transistors forming a Schmitt Trigger circuit and the output transistor. Hmmm...

    I's probably still do it with a ULN2004 because the little puppies are so reliable. And, I could use the spare sections for the mic preamp circuit. Or do the whole thing with a dual or quad opamp or comparator. Lotsa options.

    Yllis - please post your working voice trigger circuit.

    ak
     
  6. Bluejets

    Bluejets

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    Oct 5, 2014
    Also easily done with Arduino if you are familiar with them.
     
  7. Yllis

    Yllis

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    May 1, 2018
    Thanks for all the answers.
    A simplified picture of my trigger circuit is attached. As you can see I've kept this as analogue circuit, and I'd like to keep it that way. I use PICs for my other projects so I've had the option to add a microcontroller, but decided against it. A very short description of the circuit: The thrower is operated with 12V car battery, and this circuit takes its power from that same source using a 5V voltage regulator. The microphone signal is amplified with GL386 and this goes to the bar display driver (LM3914N). The highest volume led is attached to a monostable 555 timer, because the thrower needs approximately 1s pulse (or several short ones accumulating to approximately 1s) to be activated. The 555 output goes to 2N3904 transistor which operates the thrower.
    I already have some ULN2003A's and ULQ2004A's in my inventory, so using these sounds perfect. I haven't yet figured out how to use these to solve this problem, but I'll do some digging.
     

    Attached Files:

    Last edited: May 2, 2018
  8. Yllis

    Yllis

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    0
    May 1, 2018
    Hmmmm, I've been going through these answers and I have to admit that I can't figure out what you meant. It seems that my understanding of analogue circuits is not at adequate level on this.
    Could you be so kind and elaborate a little?
     
  9. AnalogKid

    AnalogKid

    2,349
    658
    Jun 10, 2015
    Which part? Specific questions?

    ak
     
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