Morse code flasher

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.

Reply to
Gavin Philpott
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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

Reply to
stratus46

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

Reply to
ehsjr

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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.
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Reply to
John Fields

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

Reply to
ehsjr

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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
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Reply to
John Fields

that

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

Reply to
ehsjr

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

Version 4
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Reply to
John Fields

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

Reply to
Rich Grise

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.

Reply to
Gavin Philpott

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I don\'t know for sure, but I\'d guess that it needs to be connected
to circuit GND.  Try it both ways and see which works best. If it
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Reply to
John Fields

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