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SCR info needed for sound activated light Morse Code

Discussion in 'Electronic Basics' started by Vin Collins, Feb 22, 2006.

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  1. Vin Collins

    Vin Collins Guest

    I need to transform audio morse code into flashing light morse code.

    My goal is to drive a light bulb to flash morse code from an audio speaker
    level source output. (cassette player).

    My grasp of the use of SCR's is very limited, but I was thinking of using a
    12.6v
    filament transformer in series with an SCR and a light bulb, then use the
    audio output (external speaker) from a small cassette player to drive the
    gate of the SCR. I am assuming the gate will detect the audio and drive the
    scr junction into conduction to light the bulb visually displaying the dots
    and dashes as flashing light.
    What general use SCR available at Radio Shack might work in this
    application.

    Any help appreciated.

    thanks,

    Vin Collins
     
  2. John Fields

    John Fields Guest

    ---
    Excellent description of what you want to do, and I can't see any
    reason why it won't work, but I'd go for a TRIAC instead of an SCR
    in order to get both halves of the 60Hz to drive the lamp.

    Unfortunately, I can't help you with what RS has in stock, since a
    search for "TRIAC" on their site goes basically nowhere.

    The good news is you should be able to use pretty much any TRIAC you
    can find as long as it can handle the lamp current and your cassette
    player can supply the current to turn it on.

    The bad news is...
    Oh, wait... there isn't any bad news.

    Your filament transformer will provide isolation from the mains, and
    as long as your cassette player's got the guts and the TRIAC can be
    fired in all four quadrants, you're home, free.

    :)
     
  3. Ken Taylor

    Ken Taylor Guest

    Look for a VOX circuit, normally used for such functions as operating a
    transmitter PTT upon audio being present. Use it's output instead to
    drive a relay (solid-state or not) and then a light bulb.

    Here's a starter, but by no means the only circuit around:
    http://www.rason.org/Projects/basicvox/basicvox.htm

    Cheers.

    Ken
     
  4. David Harmon

    David Harmon Guest

    On Wed, 22 Feb 2006 16:29:42 -0600 in sci.electronics.basics, John
    Radio Shack has some Solid State Relay modules that I'd prefer for
    the isolation.
     
  5. John Fields

    John Fields Guest

     
  6. John Fields

    John Fields Guest

    ---
    Since he'll be using a filament transformer to drive the lamp he'll
    already have adequate isolation from the mains, plus there's (maybe)
    the issue of driving the relay with AC.

    In any case, I went to their site and couldn't find any solid-state
    relays. Got a link?
     
  7. Anno Siegel

    Anno Siegel Guest

    Even if it didn't, if the audible signal is anywhere near typical
    morse speed, the eye won't be able to follow. Optical morse signalling
    is *much* slower than acoustic.

    Anno
     
  8. Vin Collins

    Vin Collins Guest

    John,

    Thanks for your input, I was fairly certain I could do it this way. I looked
    into VOX ckts and comparators etc,,,
    Sometimes really simple ckts are best, and for a simplton such as myself
    simple is about the only way to go.

    BTW: This project is so I can prepare for a US Coast Guard flashing light
    exam. Flashing light requirement for the exam is around 6 WPM.

    Thanks again,

    Vin Collins
     
  9. If you were able to use an LED as the flasher, things could become
    *much* less complicated...
     
  10. David Harmon

    David Harmon Guest

    On Thu, 23 Feb 2006 06:35:51 -0600 in sci.electronics.basics, John
    You're right.
    I saw them in bubble packs hanging from a hook. But maybe that was
    too far in the past. I couldn't find links to the triacs or SCRs
    either.
     
  11. Chris

    Chris Guest

    Hi, Vin. I happened to stop by the local Radio Shack, and found out
    some bad news. Yet once again, Shack management is alienating
    hobbyists, this time by reducing the variety of components in their
    drawers (only available at some stores). SCRs are long gone, and the
    last triac (276-1000, 400V/6A) has recently been obsoleted, and can't
    be reordered.

    Without having more information on your cassette recorder and speaker,
    you have to make some assumptions. Personally, I would like to get a
    somewhat higher voltage at the gate of the SCR or triac in the circuit
    Mr. Fields is talking about (they won't always reliably trigger with
    less than 2V at the gate), so I'd add a couple more components to give
    you something like this (view in fixed font or M$ Notepad):

    |
    | 12.6VAC .-. 12.6VAC .-.
    | o-----( X )------. o-----( X )------.
    | '-' | '-' |
    | Lamp | Lamp |
    | | |
    | | SCR | Triac
    | 0.1uF V S4006 0.1uF _|_ Q4006
    | || ___ - || ___ V_A
    | o-||-o-|___|-o--/| o-||-o-|___|-o-//|
    | Sig In|| | 10 | | Sig In|| | 10 | |
    | - .-. | - .-. |
    | 1N4001^ 100| | | 1N4001^ 100| | |
    | | | | | | | | |
    | | '-' | o o '-' |
    | | | | | | |
    | Com o----o------ o---' Com o----'------oo---'
    |
    (created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

    Tie the red speaker wire to Sig In, and one of the transformer
    secondary leads to 12.6VAC. Tie the other end of the 12.6VAC
    transformer secondary to COM, along with the black speaker wire, and
    you should be OK. With the SCR or triac shown, you should have no
    problem using a 12V bulb of up to 12 watts or so.

    You can substitute just about any triac which has conduction in all
    four quadrants for the one above. If you need something now, you just
    might want to wander over to the local radio/TV repair shop, and see if
    they've got a NTE/SK/ECG equivalent to the SCR or Triac you want. You
    should still be able to get the other components at Radio Shack.

    You're right -- KISS (Keep It Safe and Simple) is the way to go here.
    Remember that, unless you're using an AC-to-AC wall wart, you should
    fuse the mains input to the transformer just in case.

    Good luck on the exam
    Chris
     
  12. Chris

    Chris Guest

    Sorry -- try it again, this time with a 10uF electrolytic in place of
    the 0.1uF cap:

    |
    | 12.6VAC .-. 12.6VAC .-.
    | o-----( X )------. o-----( X )------.
    | '-' | '-' |
    | Lamp | Lamp |
    | | |
    | | SCR | Triac
    | 10uF V S4006 10uF _|_ Q4006
    | ||+ ___ - ||+ ___ V_A
    | o-||-o-|___|-o--/| o-||-o-|___|-o-//|
    | Sig In|| | 10 | | Sig In|| | 10 | |
    | - .-. | - .-. |
    | 1N4001^ 100| | | 1N4001^ 100| | |
    | | | | | | | | |
    | | '-' | o o '-' |
    | | | | | | |
    | Com o----o------ o---' Com o----'------oo---'
    |
    (created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

    Chris
     
  13. Hi Vin,

    : My goal is to drive a light bulb to flash morse code from
    : an audio speaker level source output. (cassette player).

    We used to do this quite a bit (way back when). The circuit
    takes speaker level audio and fires and AC Lamp. It is/was
    called a "color organ' circuit.

    : My grasp of the use of SCR's is very limited, but I was
    : thinking of using a 12.6v filament transformer in series with
    : an SCR and a light bulb, then use the audio output (external
    : speaker) from a small cassette player to drive the gate of the
    : SCR.

    First let me tell you I've built the circuit way back when in
    the 1970's. The SCR will cause a pop noise in the audio when
    the scr switches on. Way back when we were never able to get
    the pop noise out of using the color organ circuit with an AM
    Radio speaker audio driving it. FM Radio was pretty much ok.

    So you'd want to try and use an SCR or Triac Type of device
    with an AC waveform zero cross detection/switching circuit.
    You can actually find newer scr/triacdevices, which switch
    only on the ac line voltage zero cross point.

    : I am assuming the gate will detect the audio and drive the
    : scr junction into conduction to light the bulb visually
    : displaying the dots and dashes as flashing light.

    The color organ circuits I built had frequency ranges for each
    of the 3 scrs, one bass, one mid-range and the last for high
    frequency audio. If you're using it for CW notes, the mid
    range audio filter & gate driver circuit would be set up to
    best respond and detect about 750Hz audio.

    : What general use SCR available at Radio Shack might work in
    : this application.
    : Any help appreciated.
    : thanks,
    : Vin Collins

    Pretty much any scr they sell if you plan to use only a 12 volt
    transformer.

    I took a quick peek over on Ebay to see if anyone had vintage
    color organ kits for sale. There is a guy selling what looks
    like the same 3 channel circuit I built back in the 70's from
    a magazine. One seller is Hobbytron so I went to see if they
    also sold on the web.

    I'm sure if you search google for color organ circuits, you'll
    find some example circuits. I located hobbytron.com ... they
    seem to sell kits, which might be just what you want.

    They had a 3 channel color organ kit for about $29 When I
    searched "color organ" on their main home page I saw they also
    have a single channel color organ kit for $9.95 The single
    channel kit has the parts and pc board to get going if you'd
    like to go that direction.

    Good luck,

    cheers,
    skipp
    www.radiowrench.com/sonic
     
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