Another LED pulse :)

Discussion in 'The Projects Forum' started by kw0me, Jul 5, 2012.

  1. kw0me

    Thread Starter New Member

    Jul 4, 2012
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    Is it possible to run this circut on 3v? what would need to be modified? I want to pick you brains!

    My only 2 power supplies for this circut are 2v or 3v, so im using the 2v for control (working on getting it down to 1.4 max) using a solid state relay (smd tiny!) and 3v to try and power this. also again using surface mount components to make it as small as physicly possible.
     
  2. kw0me

    Thread Starter New Member

    Jul 4, 2012
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    If its not possible im thinking of making a micro 3v to 9v converter and run it off 9v.
     
  3. MrChips

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    Oct 2, 2009
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  4. kw0me

    Thread Starter New Member

    Jul 4, 2012
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    so if i use one of these joule thieves my circut will run?
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    It certainly works for one LED.
    Bare in mind that the Joule Thief circuit produces a flash on the LED. You have to increase the flash rate to make it appear continuous.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You need to specify what solid state relay you're thinking of using.

    Most SSR's are low frequency AC only, as basically the input side is an infrared LED, and the output side is an SCR or TRIAC; once you turn on an SCR or TRIAC, they stay on until the current flow through them falls to nearly zero. So, if you try to use one with DC, it'll turn on and stay on until you turn the supply off.

    The portion of the circuit you can't change has eight LEDs in parallel, and each LED has a 22 Ohm resistor.
    If each LED requires 20mA, then you need 160mA for all 8 of them.

    Your 47 Ohm resistor would have 7.52v dropped across itself with 160mA flowing through it.

    A 22 Ohm resistor with 20mA flowing through it will drop 440mV across it. 7.52+.44=7.96v

    Your LEDs could drop anything from 1.2v for IRs, 1.7v for red, to 3.8v for blue or white.
    12v - 7.96v = 4.04v. So, you'd wind up with somewhat more than 20mA current through your LEDs if they were white, and powered by a 12v battery.

    A typical Joule Thief supplies enough output to light up a single white LED from a 1.5v battery, and the light is pretty bright with a fresh battery. I frankly don't know how much power out you'd get from one with 3v, as that would be highly dependent on what transistor you used, the value for the base resistor, and the transformer. The 2N3904 is rated for 200mA max, but a more realistic value is 100mA for typical output current; which is not sufficient for your project.
    The 2N4401 is rated for 600mA max, but 300mA is more realistic - that would probably work OK.
    The 2N2222 is rated for 800mA max, with around 450 being a realistic max - that may work a bit better.

    I happen to have some toroids very much like those on the evilmadscientist page. Your mileage will vary significantly.

    You don't have your general location in your profile. You should edit your profile (under User CP) and at least give your time zone so we have an idea where you are; this helps a great deal for when we might suggest parts/suppliers.
     
    Last edited: Jul 5, 2012
  7. kw0me

    Thread Starter New Member

    Jul 4, 2012
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    I think I may have chosen the wrong words here.... I want the LEDs to fade on and off. I am unsure on the resistor value before the LEDs I'm just guessing that until the part arrives. There is no problems with running the LEDs my drama is the fading circut. Im under the impression that 3v is to low for a 555 so looking at alternate ways. Worst case I have a miniture step up 3-5v that will just fit in the case I have a 500ma or 1a version of it.

    With the ssr I did not know this about them. So how would you go about using a 2v signal to turn on and off 3v with no common ground an keepin them seperate?

    So what I'm trying to do is when the 2v goes live the LEDs fade on then when it goes dead they fade out.

    Oh and I live in Australia
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    If you won't have a common ground, then you won't get the LEDs to turn on, as you won't have a complete circuit.

    You must somehow have a complete circuit.
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    LED color?? If isolation is needed, try opto coupler; 2 V is enough for IR LED in coupler. C555 will work on 3 V. Limited drive. Consider PWM for ramp up & down. Maybe all on 3V?
     
  10. kw0me

    Thread Starter New Member

    Jul 4, 2012
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    There are grounds but they are seperate, one 2v and one 3v im using the 3v to power the fader part and leds. The 2v powers a motor wich I'm using as a signal to turn the LEDs on.

    I have found a solution to my control problem! Smt reed relay. Extreemly small and uses dc!

    Just waiting on a few more components to arrive to make the new circuit. Busted out the bread board and made the circuit it works on 12v and 9v without modification but according to my simulator it won't run on 5v without some changes one is to drop the 1.5k to 200r change the 47 for a 10 and delete the 100 before the pot. Does this sound right?
     
  11. kw0me

    Thread Starter New Member

    Jul 4, 2012
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    Oh and can anyone tell me if there's a difference between a 1000uf 25v electrolyic capacitor and a smt 1000uf 25v apart from the size?
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I see no difference.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    One has leads, the other doesn't?
     
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