extending led throbber using optoisolator?

Discussion in 'The Projects Forum' started by compudude86, May 17, 2011.

  1. compudude86

    Thread Starter New Member

    May 17, 2011
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    multiplehello,
    I have an LED throbber circuit I found online, it uses a 555 to ramp an led up and down at various intervals. however, I have many more LEDS that I want to do the same thing. would it be possible to put an optosiolator in place of the LED then feed my power through to the multiple LEDs and have it work that way? if so how would I install the optoisolator? any better ideas?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Welcome to AAC!

    The transistor you have doesn't have enough gain, and since the voltage will swing between 1/3 and 2/3 Vcc, you probably need 9VDC.

    I've explored this circuit pretty thoroughly.

    LEDs, 555s, Flashers, and Light Chasers

    Chapter 12 - Special Effects

    Figure 12.1

    [​IMG]

    Figure 12.2 shows how to do it with many more LEDs.

    [​IMG]

    As long as you pay attention to the restrictions of LEDs, there is no minimum voltage for the power supply.
     
  3. #12

    Expert

    Nov 30, 2010
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    I don't think you need an optoisolator. You already have a driver transistor in place, just have it drive the LEDs or have it drive a better transistor (higher voltage, higher current, better heat dissipation, etc.) and have that one drive the LEDs.

    Bill got here 2 seconds before I did, but I see he also did not use an optoisolator to achieve what you want.
     
    Last edited: May 17, 2011
  4. KJ6EAD

    Senior Member

    Apr 30, 2011
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    How many LEDs? What color? What supply voltage?
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Neither does the OPs circuit. It also doesn't have a current limiting resistor, which is a must for all LED circuits, no exceptions. The LED and transistor are toast in this schematic.

    [​IMG]
     
  6. compudude86

    Thread Starter New Member

    May 17, 2011
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    I am aware of the current limiting resistor problem, It is a copied schematic from a youtube vid and it was noted on that page that it was missing the resistor. thank you for catching that or I would've probably forgotten it.

    the problem is I need to raise the voltage of the leds to about 14 volts and I need the circuit to be as low drain as possible.

    I came up with an idea, to use an LED and a photocell "heatshrinked" together, link the circuit to the led and the load to the photocell so that the pulsing LED will also change the resistance on the photocell at the same time, and thereby gradually adding and removing resistance, making the other leds rise and fade. I will be looking at those other schematics, but power consumption, as it will be on a battery, is the biggest issue.
     
  7. compudude86

    Thread Starter New Member

    May 17, 2011
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    v
    green, incoming voltage 14 but the leds take 3.2-3.6 volts, about 20 of them though for power consumption I might scale it back.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    You can get good results with 14 volts. Figure 12.2 is much more complicated, but will not get warm, while 12.1 will get extremely hot. Care to guess which one will use a lot more battery juice?

    I suspect the 12.2D schematic is what you need, and it will be very energy efficient. 20 LEDs are no problem.

    We will need to pin those LED voltages (called Vf) down for optimum performance. You can measure them very easily, and will need to. LEDs are all over the place Vf wise, but as a group they tend to be very consistent.
     
  9. compudude86

    Thread Starter New Member

    May 17, 2011
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    makes sense, but what are the parts lists for the 12.2 schematics? i.e Q3 or U3b?
     
  10. Wendy

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    Mar 24, 2008
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    Depends on how you define a parts list. The parts are on the schematics themselves. You need to look at the total picture, such as U3A (which is labeled, common to all examples). U3 is a comparator, two comparators that will work are shown off to the side of the illustration. As for the transistors, you will find references to the parts I use elsewhere in the article, it is meant to be read as a whole. Be it as it may be, the exact parts are not that critical.

    What part of the world are you?
     
  11. KJ6EAD

    Senior Member

    Apr 30, 2011
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  12. KJ6EAD

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  13. Wendy

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    I tend to follow a different philosophy in my designs. I go for the easiest parts you can get. All of the parts on schematics 12.1 or 12.2 can be bought from Radio Shack, though I would be the first to point out you can get them much cheaper elsewhere.

    Q1 - NPN 2N2222A
    Q2 - PNP 2N2907A
    Q3 - IRF510
     
  14. KJ6EAD

    Senior Member

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    I'm always trying to reduce parts count and improve efficiency so I tend to look for single chip solutions whenever it's practical.

    This project could be implemented with a 556 and 2 or 3 CL320's. It would require a few passive components to set up the timers for PWM, but no resistors on the LED chains.
     
    Last edited: May 18, 2011
  15. Wendy

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    Reducing parts is important, but the ability to get the parts is probably more important. There is also a cost savings in using standard parts as opposed to specialty items requiring special orders. While not always the case there is also the cost differences, which can be significant.

    My cost for resistors is 2¢ each. Not everyone can save this much, but it is pretty common. 555 is around 35¢, as is LM393's. MOSFETs run between 25¢ and 99¢. I bought a nice quantity 1000 pack of PN2222A's for $13. You get the drift. Cost and availability counts.
     
  16. KJ6EAD

    Senior Member

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    I haven't shopped the CL320's lately but the various darlington arrays are readily available for 75¢ or less.

    I usually try to offer an array of options to the OP, unless or until he/she decides to limit for time, cost, size, power consumption, etc. Some of us want to experiment with new, unfamiliar or interesting parts from time to time.
     
    Last edited: May 18, 2011
  17. Wendy

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    I spend a lot of time on this site designing and drawing for the other guys. That and writing articles. I don't do as much experimenting with new components, I'm too busy making old ones do new things (and a lot of old things differently).

    The area I live in has several (3 actually) good electronic stores, not counting Fry's, MicroCenter, and Radio Shack. I keep pretty busy, and like the standard stock set I'm using.
     
    Last edited: May 18, 2011
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