Connect with us

Morse code flasher

Discussion in 'Electronic Basics' started by Gavin Philpott, Feb 2, 2006.

Scroll to continue with content
  1. Hello,

    I'm trying to make a device that can convert a Morse code audio file to a
    flashing light. I have the Morse message recorded as a music CD consisting
    of 800Hz tone for the dots & dashes & silence for the spaces. I want to be
    able to convert the audio output from the CD player to an on/off signal that
    I can use to flash a light. (the idea being that I can 'flash' a message by
    pressing play - this is to be used to repeatedly transmit the same message
    to a several groups of Scouts on a hike).

    I have tried using an LM2719 frequency to voltage converter to discriminate
    between tone & silence but without success.

    Any ideas gratefully received.

    Gavin.
     
  2. Guest

    If the CD doesn't have any serious S/N problems, a plain old comparator
    like an LM311 should do just fine. The only catch is you might want to
    use a retriggerable monostable to convert the 800 hz pulse train to
    just the envelope and then a simple transistor driver to your LED. It
    would work OK without the MMV though.

    GG
     
  3. ehsjr

    ehsjr Guest

    Many years ago I used something like this
    on the output of a tape player (with a relay
    instead of the LED) to key my transmitter
    to call CQ. It may be as simple for you.


    +V ---[R]---[LED]--------+
    |
    /c
    Audio out --->|---[C]---| NPN
    \e
    |
    Gnd ----------------------+


    Size R to keep LED current to ~ 20 mA at
    whatever your V is.

    If a LED is not good and you need a higher
    current lamp, use something like a TIP 120
    instead of the generic NPN and remove R.
    You'll need a heatsink on the transistor
    if you go above 2W in it.

    Ed
     
  4. John Fields

    John Fields Guest

    ---
    With the audio output from the CD player probably being cap coupled
    and with no DC return for your cap, I'm pretty sure that won't work.

    This might:

    +V
    |
    [LAMP]
    |
    C
    AUDIO>---+-----[1K]--+----B NPN
    |K | E DARLINGTON
    [1N4148] [10K] |
    | | |
    GND>-----+-----------+------+

    The premise being that due to the thermal inertia of the lamp
    filament (or the persistence of human vision) the dead time between
    the 400Hz positive half-cycles doing the work won't be noticed.

    The 1N4148 is just to make sure the negative half-cycles don't get a
    chance to excessively reverse-bias the B-E B-E junctions of the
    Darlington, but with them being in series and the audio from the CD
    plaver not likely to be more than a couple of volts, it can probably
    be eliminated.

    Thinking about the [low-level] audio out from the CD, though, this
    might be a better scheme, assuming a 12V supply and a fairly hefty
    incandescent lamp load:

    +12V>---------------+-------------------+
    | |
    [1000] |
    | S
    +----------+------G IRF5210
    | | D
    C | |
    AUDIO>--[1K]--+---B 2N3904 |K |
    | E [1N5245] [LAMP]
    [10K] | | |
    | | | |
    GND>----------+-----+----------+--------+
     
  5. ehsjr

    ehsjr Guest

    Nice - he could flash morse on his car's headlights with that!
    *Far* better than the TIP 120 I mentioned.

    As I recall, the audio level was a problem, of sorts. I had to
    crank the volume of the tape player up pretty high before the
    circuit would respond.

    Regarding the thermal inertia, that's true, but I don't think
    you'd see the blink, even if you use an LED. I don't *know*
    how high the frequency would have to be before persistence of
    vision prevents you from seeing the blink, but I'd bet it is
    well below 400 Hz.

    The original circuit ought to work, though. The DC return is
    through be to ground.

    Ed
     
  6. John Fields

    John Fields Guest

    ---
    The problem is with the other end of the cap, which has no discharge
    path. Essentially what you have is a charge pump, and as the
    capacitor accumulates charge the voltage across it will build up and
    let less and less of the input signal through to the transistor.

    Run this to see it in action:)

    Version 4
    SHEET 1 880 680
    WIRE -464 320 -464 256
    WIRE -464 448 -464 400
    WIRE -432 256 -464 256
    WIRE -320 256 -352 256
    WIRE -320 256 -320 112
    WIRE -320 320 -320 256
    WIRE -320 448 -464 448
    WIRE -320 448 -320 400
    WIRE -272 448 -320 448
    WIRE -272 448 -272 384
    WIRE -176 112 -320 112
    WIRE -128 336 -272 336
    WIRE -128 352 -128 336
    WIRE -128 448 -272 448
    WIRE -128 448 -128 432
    WIRE -16 112 -112 112
    WIRE 128 112 48 112
    WIRE 192 -64 192 -96
    WIRE 192 64 192 16
    WIRE 192 448 -128 448
    WIRE 192 448 192 160
    WIRE 352 -96 192 -96
    WIRE 352 320 352 -96
    WIRE 352 448 192 448
    WIRE 352 448 352 400
    WIRE 352 496 352 448
    FLAG 352 496 0
    SYMBOL npn 128 64 R0
    SYMATTR InstName Q1
    SYMATTR Value 2N3904
    SYMBOL res 176 -80 R0
    SYMATTR InstName R1
    SYMATTR Value 1000
    SYMBOL diode -176 128 R270
    WINDOW 0 32 32 VTop 0
    WINDOW 3 0 32 VBottom 0
    SYMATTR InstName D1
    SYMATTR Value 1N4148
    SYMBOL cap 48 96 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C1
    SYMATTR Value 1e-6
    SYMBOL voltage -464 304 R0
    WINDOW 3 24 104 Invisible 0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value SINE(0 5 800)
    SYMBOL voltage 352 304 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value 12
    SYMBOL sw -320 416 R180
    WINDOW 0 -51 99 Left 0
    WINDOW 3 -91 128 Left 0
    SYMATTR InstName S2
    SYMATTR Value MYSW
    SYMBOL voltage -128 336 R0
    WINDOW 3 24 104 Invisible 0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V3
    SYMATTR Value PULSE(0 1 0 0 0 .05 .1)
    SYMBOL res -336 240 R90
    WINDOW 0 -40 55 VBottom 0
    WINDOW 3 -36 56 VTop 0
    SYMATTR InstName R2
    SYMATTR Value 100
    TEXT -402 506 Left 0 !.tran 0 1 0
    TEXT -400 552 Left 0 !.model MYSW SW(Ron=1 Roff=1Meg Vt=0.5 Vh=0)
     
  7. ehsjr

    ehsjr Guest

    Thanks!

    It's not a pretty picture. Decays to very little in .9 S.
    Disappears at 14 sec. It demonstrates your point, very well.

    You have to use a bigger C1, but after a while the same
    thing will happen. Maybe there is some combination of
    duty cycle and cap leakage that works by accident, but
    the circuit, such as it is, fails. I stuffed a 470
    in the simulator and let it run for 50 seconds - it started
    showing the decay between 20 and 30, and it was
    pronounced between 40 and 50.

    Is there a way to put a duty cycle in?

    Ed
     
  8. John Fields

    John Fields Guest

    ---
    The easiest way out, I think, is just to get rid of the cap:

    Version 4
    SHEET 1 880 680
    WIRE -624 192 -624 112
    WIRE -624 320 -624 272
    WIRE -624 448 -624 400
    WIRE -480 112 -624 112
    WIRE -480 320 -480 112
    WIRE -480 448 -624 448
    WIRE -480 448 -480 400
    WIRE -432 448 -480 448
    WIRE -432 448 -432 384
    WIRE -352 112 -480 112
    WIRE -288 336 -432 336
    WIRE -288 352 -288 336
    WIRE -288 448 -432 448
    WIRE -288 448 -288 432
    WIRE 16 112 -272 112
    WIRE 16 240 16 112
    WIRE 16 448 -288 448
    WIRE 16 448 16 320
    WIRE 128 112 16 112
    WIRE 192 -64 192 -96
    WIRE 192 64 192 16
    WIRE 192 448 16 448
    WIRE 192 448 192 160
    WIRE 352 -96 192 -96
    WIRE 352 320 352 -96
    WIRE 352 448 192 448
    WIRE 352 448 352 400
    WIRE 352 496 352 448
    FLAG 352 496 0
    SYMBOL npn 128 64 R0
    SYMATTR InstName Q1
    SYMATTR Value 2N3904
    SYMBOL res 176 -80 R0
    SYMATTR InstName R1
    SYMATTR Value 1000
    SYMBOL voltage -624 304 R0
    WINDOW 3 24 104 Invisible 0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR Value SINE(0 1 100)
    SYMATTR InstName V1
    SYMBOL voltage 352 304 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value 12
    SYMBOL sw -480 416 R180
    WINDOW 0 -51 99 Left 0
    WINDOW 3 -91 128 Left 0
    SYMATTR InstName S2
    SYMATTR Value MYSW
    SYMBOL voltage -288 336 R0
    WINDOW 3 24 104 Invisible 0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR Value PULSE(0 1 0 0 0 .05 .1)
    SYMATTR InstName V3
    SYMBOL res -256 96 R90
    WINDOW 0 -40 55 VBottom 0
    WINDOW 3 -36 56 VTop 0
    SYMATTR InstName R2
    SYMATTR Value 100
    SYMBOL res 0 224 R0
    SYMATTR InstName R4
    SYMATTR Value 10k
    SYMBOL res -640 176 R0
    SYMATTR InstName R3
    SYMATTR Value 10
    TEXT -402 506 Left 0 !.tran 0 1 0
    TEXT -400 552 Left 0 !.model MYSW SW(Ron=1 Roff=1Meg Vt=0.5 Vh=0)


    I set the generator output to +/- 1V to more closely simulate what's
    going to be coming out of the CD player, and I made it look like it
    has ~ 100 ohm resistive output impedance. If it's cap-coupled, in
    reality, it won't make any difference because R4 will provide the
    path to ground on one end and whatever's driving it in the CD player
    will take care of the other end.

    Seems to work pretty well...
     
  9. Rich Grise

    Rich Grise Guest

    Do you mean, you have a thing, with a speaker, that goes,
    "BEEP-BI-BEEP-BIP, BEEP-BEEP-BI-BEEP" audibly?

    If so it's almost trivial. Get an LED and a 220 ohm resistor, and put them
    in series right directly across the speaker leads. Turn up the volume
    until it's bright enough to suit you. :)

    Good Luck!
    Rich
     
  10. John, Ed,

    Thanks both for your help with this; I'm off to try it out. Couldn't make
    head or tail of the circuits for a start, realised I needed to view them
    with an editor with fixed font width so everything lined up!

    Just one query (its been years since I've done any of this stuff & I'm
    pretty rusty), what do I do with the ground output from the cd player?
    Connect it to the circuit GND, or just leave it floating?

    Thanks once more,

    Gavin.
     
  11. John Fields

    John Fields Guest

     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-