Any electronics wizzards out there?

uilleann

Member since
March 2004
From: Salt Lake City, Utah

Any electronics wizzards out there?

Posted by uilleann on Saturday, March 20, 2004 12:31 PM

I'm trying to figure out how to build a simple circut that will allow me to ocsillate the brightness up and down on an LED. I'm trying to simulate a rotating beacon for my next AC project.

I'd like to have control (either real-time once it's built or at least in choosing the resistor properties while building it etc.) over two seperate aspects.

1. The cycle time (rate between peak flashes)

2. The ramp up/ramp down (the time it takes to fade from off to full brightness and back down again.)

If any of you have watched an airport beacon or a lighthouse before, you'll be familliar with the effect I'm trying to achieve. Rather than a sharp ON/OFF like you get with a standard blinking LED, I'm trying to recreate the soft glow of light you see before the main beacon sweeps across the field of view. It slowly increases until the main beam is visible, then fades back again slowly.

I'm assuming I'll need some form of timing circut (like a 555) and perhaps a capacitor to achieve this. Any help offered would be MOST appreciated! Bow [bow]

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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ckfredrickson

Member since
April 2003
From: Halfway back to where I started

Posted by ckfredrickson on Saturday, March 20, 2004 4:43 PM

try looking around this site:

http://ourworld.compuserve.com/homepages/Bill_Bowden/

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Saturday, March 20, 2004 5:35 PM

WOW. OK, now to decipher it all! Shock [:O]

I gave up years ago with trying to have the local Radio Shack wiz kids explain anything. I wouldn't even trust them with explaining a watch battery!

I may be able to hack this one out though I think I will keep looking to see if I can find any simpler means of doing the same thing. Thanks though CK!

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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tweety1

Member since
August 2003
From: Alice Springs Australia

Posted by tweety1 on Saturday, March 20, 2004 8:44 PM

Some other sights you maybe find useful.

http://circuitos.tripod.cl/schem/r88.gif

http://members.shaw.ca/novotill/FireLightFlicker/index.htm

http://www.web-ee.com/Schematics/LED%20Dimmer/LED_Dimmer.htm

--Sean-- If you are driving at the speed of light and you turn on the headlights, what happens???

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Sunday, March 21, 2004 7:48 AM

Thanks Tweety,

That second one had me running for cover! What a frightening circut! LOL I think the first link I got was a little closer to the type of effect and control I am looking for - but I still have to track down the IC chip to test it. I'm most greatful for your work in looking these up for me though - THANKS!

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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tweety1

Member since
August 2003
From: Alice Springs Australia

Posted by tweety1 on Saturday, March 27, 2004 9:20 AM

Not a problem uilleann, let us know how it all goes, really interested in what the final look will be.

--Sean-- If you are driving at the speed of light and you turn on the headlights, what happens???

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MusicCity

Member since
January 2004
From: USA

Posted by MusicCity on Monday, March 29, 2004 9:39 PM

QUOTE: I still have to track down the IC chip to test it. I'm most greatful for your work in looking these up for me though - THANKS!

Digikey should have them, they are manufactured by Intersil and they carry a lot of their stuff. Their site is at www.digikey.com

Scott Craig -- Nashville, TN -- My Website -- My Models Page

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Sunday, April 4, 2004 10:33 AM

OK, so I've built this circuit twice now and I can get the LEDs to turn on..........but that's it!

http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm#eyes.gif

According to the article I should be able to get them to fade in and out at about a half second rate - but nothing. Any guesses as to what I may have done wrong? (I understand it may be difficult to diagnose without seeing the actual board)

I've used all the exact parts stated in the article. The only things I can think of *might* be the use of a polarized capacitor? I was unable to find a non-polarized cap at that size, but I wired it so the current flow was consistant with the rest of the circut. Or perhaps I got the transistor in backwards ie: the emmitter where the collector should be?

Would either of these things cause the LEDs to trun on but not to cycle do you think??

ANY help most graciously appreciated! Banged Head [banghead]

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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Anonymous

Member since
November 2005

Posted by Anonymous on Sunday, April 4, 2004 2:38 PM

If the transistor was wired backwards, there would be no current flow.
To make a 22 microfarad non-polarized, use two 47 microfarad in series wired back to back. ( The second circuit shown with the two 22's would equal 11 microfarads. )

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Sunday, April 4, 2004 3:26 PM

Does it mean something bad if the circut runs both with and without the IC chip? It does the same thing - just stays on without cycling. So if I'm getting any light at all, can I assume that the transistor isn't the problem here and it must be something else? Would a burnt out capacitor keep things from cycling?

(taking copious notes!)

THANKS SO MUCH!!!!!!!

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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Anonymous

Member since
November 2005

Posted by Anonymous on Sunday, April 4, 2004 4:39 PM

Are you sure the base of the transistor is connected to Pin 1 and not pin 3? For the LED to stay on, the base must have a bias voltage on it.
Do you have a digicam to take a pic of your circuit?

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Sunday, April 4, 2004 9:07 PM

I'm not sure (I'm not home at the moment, but will be soon) if I got the pins switched...but I'll double check it. I do have a cam at home and I'll take a few shots and see if it helps to show what I have very likely done wrong! LOL

Thanks for all your help on this one Keith!

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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Anonymous

Member since
November 2005

Posted by Anonymous on Wednesday, April 7, 2004 5:13 AM

As you are looking at the flat side of the transistor, it goes emitter, base, collector (left to right) for the transistor. As you are looking at the circuit diagram, the base is connected to the +9V. The emitter is the lead connected to the 100 ohm resistor and the LEDs. The collector comes from the op-amp/capacitor.

However, I would suggest looking at the specs of your op-amps. Have you connected them correctly, and do they have power and a ground?

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Anonymous

Member since
November 2005

Posted by Anonymous on Wednesday, April 7, 2004 12:50 PM

QUOTE: Originally posted by edog

As you are looking at the flat side of the transistor, it goes emitter, base, collector (left to right) for the transistor. As you are looking at the circuit diagram, the base is connected to the +9V. The emitter is the lead connected to the 100 ohm resistor and the LEDs. The collector comes from the op-amp/capacitor.

However, I would suggest looking at the specs of your op-amps. Have you connected them correctly, and do they have power and a ground?

The Collector goes to +9, the Base to the op-amp output!

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Wednesday, April 7, 2004 2:06 PM

Ah now I'm even more confused than before! I don't know WHICH way the CBE or EBC goes on theis stupid thing! LOL I switched it around the other way and got nothing at all - not even the steady on glow.

Have I burned it out when I soldered it maybe? I seem to recall that certain components are extremely sensitive to heat (like IC chips).

B~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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Anonymous

Member since
November 2005

Posted by Anonymous on Wednesday, April 7, 2004 2:45 PM

When looking at the transistor with the flat side facing you, it goes EBC.
If it is wired backward ( CBE ), there won't be any current flow and the led won't light. If the led is on continuously, then it is likely that the base always has a
bias voltage on it. If you have a multimeter, measure the voltage between ground and the base ( middle lead ) of the 2n3904. And yes, they are sensitive to excessive heat. At least the 2n3904 is cheap and easily found. BTW , I built the circuit myself on a breadboard, and it does work, however you might want to play with the value of the capacitor between pins 1 & 2 to get the desired delay rate. Approve [^]

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Anonymous

Member since
November 2005

Posted by Anonymous on Wednesday, April 7, 2004 5:10 PM

yah sorry, Copierguy is right, i was wrong about the circuit diagram. thats what is what i get for posting at 3:30 in the mourning. I would still make sure you have the op-amps hooked up correctly though. That would be my best guess...

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Anonymous

Member since
November 2005

Posted by Anonymous on Wednesday, April 7, 2004 5:42 PM

just thought of another reason: check your capacitance value. if this is wrong, it may be flashing so fast, that you can not tell that it is blinking.

Oh, and the circuit worked for me too.

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Anonymous

Member since
November 2005

Posted by Anonymous on Wednesday, April 7, 2004 8:54 PM

I found that too edog. I Ended up with 66 microfarads in series with a 500 ohm trimmer pot to slow down the blink and decay rate.

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Anonymous

Member since
November 2005

Posted by Anonymous on Wednesday, April 7, 2004 10:54 PM

WOW, didn’t think of that. It worked great. Variable seed baby!! LOL!! Honestly, I have not designed many circuits; just put them together for lab and I have done a lot of “what the H#LL is wrong with this thing!!”

So, let me see… The greater the capacitance, the more the capacitor has to charge, making it slower, but the light should be brighter, right? I am using about 20uF and it is pretty dim, but I also had to use 55k resistors for the bridged input, and I’m not sure how this affected the current. Hmmm, I have gotten too used to Pspice… Now i sound like a real geek!

Brian, from the sound of it, you will be doing a lot of lighting for your models. It might be worth investing in a proto, or bread board for testing the design.

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Wednesday, April 7, 2004 11:06 PM

Hey Edog,

I do have a breadboard, but I was cheap and bought the kind that is too skinny to fit the dumb IC holder base thingy into! Dunce [D)]

And I still can't get the circut to work right! Tell yous guys what! Can I pay you for parts and your time and would you be willing to send one all soldered and finished off to me? Big Smile [:D]

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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Anonymous

Member since
November 2005

Posted by Anonymous on Thursday, April 8, 2004 9:46 PM

Brian,

Tell you what... I will make a VERY detailed diagram for you to follow, and if you have enough patients, you can try it again. If that does not work, I will be happy to make it for you. Big Smile [:D]

sound like a plan? Give me the weekend, and I will try to come up with something for you. Sorry, I have 3 projects to do, an exam on Tuesday, finals is just around the corner, plus I have to see if I can hunt down an internship, among other daily duties. Dead [xx(]

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Thursday, April 8, 2004 10:41 PM

Thanks edog. :)

I thought I had followed everything pretty precisely, but I must be missing something. Ah well - humility is a virtue.......or so I'm told. LOL Take your time and just let me know if/when you have a chance to draw it out.

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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Anonymous

Member since
November 2005

Posted by Anonymous on Friday, April 9, 2004 3:28 PM

ok, here is how the op-amp chip should be hooked up and the transistor when looking down at the top of each. I just wanted to make sure you have them correct. If you still cant get it, let me know. for some reason, a few of the lines are missing on the post, click on the image, and it should be ok.

good luck

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Friday, April 9, 2004 4:40 PM

Right - got it! That bit seemed pretty straight forward from the get go...and I switched the transistor at the suggestion of the circuit's designer.

Anyway, I'm putting a new one together as I type this (sort of! Approve [^]

) and will let you know how it works out.

Thanks for all the help on this silly thing!

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Friday, April 9, 2004 8:53 PM

Interesting!

Now that I've got this little multimeter thing going here, I've made a most peculiar discovery! The 9v 100 mA power supply I've been using tests at an actual voltage of 14.70!!! My meter doesn't read amperage that I can tell...but WOW!

I'm off to the store this evening to see if I can find a 500-600 ohm pot to bring things back down inline with the 9v needed. Just goes to show you can't trust what's satmped and labeled on the back of these things!

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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MusicCity

Member since
January 2004
From: USA

Posted by MusicCity on Friday, April 9, 2004 9:30 PM

Are you measuring the voltage with a load on the power supply or without any load or with a circuit laod? The unloaded voltage will always be higher. Once you put some load on it, it should drop down closer to what you expect.

Scott Craig -- Nashville, TN -- My Website -- My Models Page

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Anonymous

Member since
November 2005

Posted by Anonymous on Friday, April 9, 2004 9:35 PM

have you tried a 9V battery?

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uilleann

Member since
March 2004
From: Salt Lake City, Utah

Posted by uilleann on Friday, April 9, 2004 11:02 PM

Yes, yes and yes. Big Smile [:D]

The voltage was reading between 14.70 and 14.75 in the circuit. I popped in a 100K pot and trimmed it down just a touch and VOILA!!!!!!!!!

IT WORKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Freakin' cool!

Check out a short video here of the real thing and my silly circuit:

http://saltlakepipers.com/F-117/Beacon-Video.wmv

Thanks SO MUCH to all for your tireless help and suggestions!

Bri~

"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"

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Anonymous

Member since
November 2005

Posted by Anonymous on Saturday, April 10, 2004 1:41 AM

I hope your 100k pot is rated at least 1 watt. Shock [:O]

Glad you got it running!

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