Morse code flasher

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

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.

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

--- 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:

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:

-- John Fields Professional Circuit Designer

Nice - he could flash morse on his car's headlights with that!

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

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

On Tue, 07 Feb 2006 09:18:46 GMT, ehsjr wrote:

--- 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...

-- John Fields Professional Circuit Designer

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

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.