Super Newbie with big Project in Mind

Discussion in 'The Projects Forum' started by 3lectror3ad3r, Jan 9, 2008.

  1. 3lectror3ad3r

    Thread Starter New Member

    Jan 9, 2008
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    Hello I found this site in the Electronics for Dummies book and decided to see if I could build the project of my dreams. :D I have no clue where to start so hopefully you guys at this awesome site :D can help me.

    Here we go My idea consists of a LED array of about of about 20 LEDs in a complete circle . I would like to hook up these arrays to a dimmer and depending on the amount of current I would like the LEDs to light up in a series of three rings. So at low current one ring will light up, medium the second ring of lights will light up and finally high all of them would light up in a 1..2..3 sequence. This is my idea that I would like some direction to starting. I would like to make this a reality so if anyone could help me out? you have my THANX. Looking forward to becoming a longtime member here.

    ~3lectror3ad3r~
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    A sketch of your LED layout might be helpful.

    hgmjr
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    So, you want the inner ring to light up first, right?

    In your vision here, do you plan on the LEDs to start off being dim, gradually becoming brighter? Or to illuminate from off to bright, just in order?

    Were you planning on using all the same color of LEDs? If yes, which color?

    Do you have a specific part#(s) in mind for the LEDs? If not, do you know their voltage @ current rating?
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    We hate to pepper you with questions but some clarification is needed if we are not to waist time, yours and ours.

    Are there a total of 20 LEDs or are there three rings times 20 for a total of 60 LEDs?

    hgmjr
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    From what I gather, he wants to have three LED rings. The inner ring will go from zero intensity to some value, then the next ring will turn on. It will light from zero to some value, etc. He wants to control it with a single potentiometer..

    I think the best way would be PWM of the LEDs. So, there would be three PWM circuits that accept a 0-some voltage level for 0-100% PWM. The potentiometer would give a voltage from 0 to supply. This voltage would be fed into two comparators, each set up to turn on FETs to the two higher LED chains. The voltage would be divided down for properly controlling the PWM for the higher stages via two voltage dividers.

    That's the simplest way I can think of, maybe something linear would be nice. I like efficient though, so PWM is the way to go :D

    Steve
     
  6. scubasteve_911

    Senior Member

    Dec 27, 2007
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    I was thinking, if logic level FETs were used, you can simply AND the comparator output with the PWM signal. This way you save that extra FET on the two upper rings.

    Steve
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    I'm thinking two 556's, 1/2 of each per ring set up as monostable MV's, and one as a VCO. The outputs can sink 200mA, which if he uses a 12V supply, will be plenty to sink the power in an array of 20 diodes.

    If the diodes are connected in each ring as 4 in a series string with 5 strings, with a 150 Ohm resistor on the V+ end (ballpark number to limit current to 15mA, actual value depends upon the LED rating) three of the 556 halves would need to sink 75mA each (maximum), well within the 200mA specification.

    The halves of the 556s that sink power are set up as monostable multivibrators (MMV). The center ring gets the longest duration pulsewidth, the next ring out gets a shorter pulsewidth, and the furthest out gets an even shorter pulsewidth. As the astable voltage controlled oscillator (VCO) half triggers the monostable halves more and more frequently, they will gradually provide more power to the LEDs, according to the voltage level on the CTL pin and how long the respective pulsewidth is.

    Two IC's, and a bunch of LED's, perhaps 2 dozen resistors and a half-dozen caps or so. He could even use DIP resistors to reduce parts count if he wanted. Then there's always the quad 558 timer... but that might be hard for him to obtain locally.
     
  8. 3lectror3ad3r

    Thread Starter New Member

    Jan 9, 2008
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    Wow thanks for the replies and wow i've only dabbled with electronics with simple projects. Reading some of your posts is...wow...but i'm willing to learn each and every term that was used thanks for the reply and help. Guess i have some research and reading to do. If anyone could suggest some sites that i can reference and possibly build project that utilizes some of the components mention would be greatly appreciated. Thanks again :D

    ~3lectror3ad3r~
     
  9. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    Wookie's approach is more elegant :) I never really dabbled with the 555, eventhough it lends itself to things such as this.

    Steve
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    My best suggestion is to go down to your local Radio Shack and pick up an Electronics Learning Lab. They're $65, and it's worth that for just the lab board itself.
    http://www.radioshack.com/sm-electronics-learning-lab--pi-2102913.html
    It comes with a number of CMOS IC's, resistors, caps, jumpers, and two workbooks. The lab was designed and written by Forrest M. Mims III, and he did a super job on it. You'll also need six "AA" batteries to power it.

    Instead of alkalines, I suggest getting a set of NiMH batteries, and a battery charger designed specifically for NiMH batteries.

    What color of LEDs did you have in mind for this project? It really does affect the design. Red, green and yellow are generally between 2.1 to 2.7V, but aqua, blue and white can run up to around 4V.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Are you still with us? Did you decide on an LED color, or colors yet?
     
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