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Last night I'm in my one of my favorite watering holes. The bar has recently set up a DJ booth (and trust me - when the DJ starts up, I find another watering hole). Somehow the conversation comes around to the DJ decks he's installed - some kind of heavy duty Technics POS built to be jumped on by 500lb gorillas and dragged through the mud and still play what they call music.The guy I'm talking to _insists_ that the timing light on new decks is a "laser". I try telling him it's a strobe light, probably just an LED. I can't convince him that the thing works because it's being strobed and that it's not a steady light, even though it may appear to be.
How can I visually "prove" to him that the timing light is being strobed?
Follow Ups:
There are far better things to do, and they'd look at me like I was an idiot.. (they'd be right)..:-)Have him stop the platter, then have him sweep his vision back and forth past the light, he'll see the stobing.
This is the same thing that the newer taillights do when they are not braking, but the headlights are on.
"The easiest way to confound a wise man is to pit him in an argument with a fool, for there is no arguing with a fool"Ivy league graduates can be just as bad. Seems to be an illness of the time. And it certainly is an illness in sound reproduction opinions.
First, ask the person how the light "freezes" the motion if it is on continuously. The fact that a laser emits coherent radiation is irrelevant for freezing action. The light must be strobed.If you have or can borrow a digital camera, this shouldn't be too hard. I'll give two demonstrtions, the first a bit trickier, but more graphic, and the second very easy. For the first one, set the camera to take about 1 second exposure or so. A bit shorter or longer won't matter. Make sure the light itself doesn't look too big, say smaller than about 1/4 inch, by covering it with some black tape. Now simply take some exposures in focus from a few feet away- darkening the room would be very good- and as you take the picture, let the camera turn so that the stobe light starts at one edge of the picture as the shutter opens and one second later, at the end of the picture, it is at the other edge. You may have to try it a few times to get it right, but what you will see is not a continuous streak, but a series of dashes corresponding to the times when the lamp was on. This is probably easier to do than to describe.
The second test is to simply set the exposure to less than 1/120 of a second, and take a numer of pictures of the light. This will be hit and miss, but on some the light will be on and others it will be off. In this case be sure you can see the turntable in the picture, as if no light and nothing else is visible, it could be claimed the camera didn't work.
Another easy way: take two LEDs, hook one to a battery, and have them stare straight ahead while you move it around in front of them. It will look like a "solid line" (sort of like the photo of Picasso drawing the bull in the middle of the air, in the dark, in one very long exposure).Take the other LED and connect it to an unrectified (AC) wall-wart. If it's more than 3V, stick a 560? to 680? resistor in series with one lead, and don't go past 15V or so. Anyway, when you move this one around in front of them with them staring straight ahead, it will appear to blink rapidly.
If they STILL won't believe you, pick up their turntable and wave it around in the air in front of their face!
Ok, the two question marks actually were typed in as omegas, don't know why it didn't post that way, sorry.560 Ohm to 680 Ohm
ΩΩΩΩΩΩΩΩ
John,The omegas look fine in the post, but the ones that came out in the e-mail from AA looked like this:
ΩΩ, etc.
Arrrgh!
on my keyboard, the key combination for omega is "option-z", works in any font, and shows up just lovely in this window as I'm typing - ? - but doesn't come out that way. I'm assuming to make it work, I'll have to use a key combo that looks like a really weird character on the screen, but comes out fine in a web browser. Hmmm...
You guys can ignore the rest of this post, just gonna experiment a second -
Møøse, Â Måjëstik MØØSE. ?r not square, ?r round. This is definitely not my ƒorte, or is it ?orte? I must have a µ-sized brain to keep doing thi?, or is it thi??
BT®
hope this woiks..http://db.audioasylum.com/cgi/m.mpl?forum=prophead&n=14201&highlight=8859+jneutron&session=
Cheers, John
Use html code.."omega" is ampersand pound 8486, no spaces.
I'll find the prop post where I posted every valid ISO-8859 character.
Next time you're there, point a flashlight at the strobe markings on the platter. You will not see the strobe effect because the light from the flashlight is not strobed since it operates on direct current. By the way, most if not all light sources operating on 60 Hz line power are "strobed" at 60 Hz - remember the amplitude must go to zero in order to reverse. Pretty basic stuff.
Get a small silicon solar cell, single cell 0.5vdc output, low current will do. (RadioShack or any electronics hobby outfit). Wire a high impedance earphone or headphone to the solar cell.Point the cell at the strobe light and you should hear 33 1/3 Hz (or whatever speed the TT is set to). Vary the speed of the TT and the tone should vary accordingly.
Point the solar cell at the room lights, you should hear the 60Hz buzz.
----------BTW, my 7th grade science project used a small transformer output transistor amplifier (about 500mW) feeding a small incandescent flash light bulb (with 1.5v battery in series to "bias" the bulb ON to keep it warm). At the other end was a solar cell feeding an audio amplifier. Along with some focusing lenses, it was my "talk on a light beam" science project. This was a simple AM light beam project. I later graduated to PLL based FM system.
< < How can I visually "prove" to him that the timing light is being strobed? > >Just take your hand and spread your fingers apart. Now wave your hand rapidly back and forth in front of the light. You will see a "strobe-like" effect, vaguely similar to the strobe lights used on the dance floor. Works with digital bedside clocks too, as the segments are multiplexed (not on all at once, but instead one at a time in rapid succession).
:)
dots on the platter edge are arranged so they appear stationary when the table is turning at the correct speed and the light is strobing at the frequency of the line voltage. So probably for 60 Hz and 33 1/3 RPM some multiple of 108 dots along the circumfrence of the platter, 80 for a 45 RPM.
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