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It's not flashing! :(

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It's not flashing! :(

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Old 05-05-09, 11:53 PM
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It's not flashing! :(

The darn clock generator is not flashing



...according to the simulator, it's supposed to flash... at around 500Hz



I'm in despair... why they teach logic circuits BEFORE analog if they are gonna ask me to make sequential machines that require a darn clock, which I can not construct without the analog knowledge? ... despair

PS: Is my camera good?
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Old 05-06-09, 05:09 PM
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A trip to the cubicle of the local electronic weenie revealed that it is indeed flashing (the guy has a 5k oscilloscope on his cube) , it's just so fast that the led never discharges and appears to be on all the time. Gonna have to play with the values of R1, R2 and C1 to get the frequency down to about 1Hz... that will do... probably with a 10% duty cycle.

PS: No, I don't know what I'm doing.... yet.
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Old 05-06-09, 05:43 PM
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I was going to say that I don't think they make LEDs that are capable of flashing at 500Hz. But someone already told you this.
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Old 05-06-09, 06:26 PM
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flasing is a difficult concept.
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Old 05-06-09, 07:54 PM
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you shouldn't be able to see flashing at 500 Hz. If you've ever looked at the 100'ths place of a digital watch, it's just a blur. And 1/100th of a second is five times slower than 500 Hz.
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Old 05-06-09, 07:56 PM
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Well, you could directly clip an oscilloscope to either side of the diode and see if you get your waveform there.
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Old 05-06-09, 11:02 PM
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Old 05-07-09, 10:24 AM
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It's not the LED that doesn't flash, it's your eye can't recognize 500Hz. That's why monitors are refreshed at 70Hz and higher so the image looks stable to you.
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Old 05-07-09, 10:28 AM
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Originally Posted by RubenX View Post
A trip to the cubicle of the local electronic weenie revealed that it is indeed flashing (the guy has a 5k oscilloscope on his cube) , it's just so fast that the led never discharges and appears to be on all the time. Gonna have to play with the values of R1, R2 and C1 to get the frequency down to about 1Hz... that will do... probably with a 10% duty cycle.

PS: No, I don't know what I'm doing.... yet.
Just saw this thread. I was going to ask you how you thought you'd see it at that rate.
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Old 05-07-09, 10:56 AM
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Originally Posted by KingTermite View Post
Just saw this thread. I was going to ask you how you thought you'd see it at that rate.
High-speed camera, perhaps?
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Old 05-08-09, 01:00 AM
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Originally Posted by KingTermite View Post
Just saw this thread. I was going to ask you how you thought you'd see it at that rate.
Light travels a lot faster and yet you can see the laser beams traveling with the naked eye on every star trek episode... even people dodging them....
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Old 05-08-09, 01:18 AM
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Originally Posted by RubenX View Post
Light travels a lot faster and yet you can see the laser beams traveling with the naked eye on every star trek episode... even people dodging them....
It's nothing to do with the speed of light. Even assuming that an LED is capable of turning on and off five hundred times per second (I doubt it), the human eye can't detect it.
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Old 05-08-09, 09:26 AM
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Originally Posted by RubenX View Post
Light travels a lot faster and yet you can see the laser beams traveling with the naked eye on every star trek episode... even people dodging them....
You could see it if it were a solid 'on' beam (like a laser pointer). It's not about the speed of the light, but about the speed of the blink and what your eye can detect.

An LED blinking 500 times per second effectively just looks 'on' to us because our eyes detect the on and the off is too quick to see. Why do we detect 'on' and not 'off' because its also off 500 times per second you ask? My guess is because our vision works on light coming in to our eyes (not lack of light)....so its the light phase of the period that is detected.
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Old 05-08-09, 09:44 AM
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Erhm... guys... the star trek thing was a joke :S
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Old 05-08-09, 09:46 AM
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Originally Posted by RubenX View Post
Erhm... guys... the star trek thing was a joke :S
I laughed at it fwiw.
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Old 05-08-09, 09:52 AM
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Originally Posted by RubenX View Post
Erhm... guys... the star trek thing was a joke :S
I know....but wanted to try to explain that better anyway.

How'd I do?
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Old 05-08-09, 09:53 AM
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Originally Posted by x136 View Post
It's nothing to do with the speed of light. Even assuming that an LED is capable of turning on and off five hundred times per second (I doubt it), the human eye can't detect it.
Depends on the LED.
An indicator LED like you can find in audio equipment and stuff like that have a max frequency of maybe a few hundred Hertz, while a laser LED in telecommunication equipment can go into the Gigahertz range, think data transfer through fiber optics in the Terabit range.
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Old 05-08-09, 10:30 AM
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Originally Posted by Scummer View Post
Depends on the LED.
An indicator LED like you can find in audio equipment and stuff like that have a max frequency of maybe a few hundred Hertz, while a laser LED in telecommunication equipment can go into the Gigahertz range, think data transfer through fiber optics in the Terabit range.
Well, yeah, but you aren't going to find one of those at Fry's... but maybe if you had a GBIC or FC card handy, you could disembowel it and get the LED.
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Old 05-09-09, 08:12 PM
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Update... success!

I have the clock flashing... not only that, it's now adjustable from around 0.75Hz to a-lot-ofHz and I also used 2 D-Type Flip/Flop to provide 2 more frequencies, clock/2 and clock/4. It's still on the protoboard but works beautifully:

Linky

PS: phone video quality not too good...
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Old 05-10-09, 03:04 AM
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Originally Posted by RubenX View Post
Light travels a lot faster and yet you can see the laser beams traveling with the naked eye on every star trek episode... even people dodging them....
It's not laser beams they're shooting. Phasers fire nadion particles.
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Old 05-10-09, 03:58 AM
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Originally Posted by DannoXYZ View Post
It's not laser beams they're shooting. Phasers fire nadion particles.
Oh my! Danny is right...

/me hands over his Trekkie card
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Old 05-10-09, 04:05 AM
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Yeah, figured it was a joke. Anyway, look into decay rates of phosphor screens and LEDs. There's a lobsided triangular graph somewhere. And different formulations have different decay rates as well. But they all tend to be faster than the recharge-rate of the cells in your eyeballs.
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