2 led questions

Discussion in 'General Electronics Chat' started by xxdcmast, Nov 18, 2004.

  1. xxdcmast

    Thread Starter New Member

    Nov 18, 2004
    7
    0
    Hey whats up everyone im new to the board and pretty new to electronics, but I am starting a project soon. Basically what I want to do is create two light bars out of 10 21000 mcd white leds to be placed under the back fender of my motorcycle right above the tire. My first question is I think I want to wire them in paralel like shown below, do you guys see any problem with how I have this set up?

    And my second question is I was thinking about using some sort of simple RC circuit to cause the leds to blink at a certain rate but have not been able to figure out the schematic for the circuit, was wondering if anyone could offer some help?

    This is how I want to wire up the leds I am running it off of 12 volt motorcycle battery so i think i am gonna need a 330 ohm resistor
     
  2. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi,

    if you want to blink, use the famous 555 timer and operate it in astable mode. for your limiter increase it to 390R up to 560R. just be sure you dont exceed 25ma. of current fed to the LEDs. :)
     
  3. Xray

    Well-Known Member

    Nov 21, 2004
    58
    1
    Hi,
    Your circuit SHOULD work, but keep in mind the power handling requirement of your resistor. For example, let's say each LED draws 10mA. If you add them all up, you have 100mA total current draw. In that case, your resistor would have to be rated at least 2 Watts, which gives you a "safety margin". If you wanted to make a flasher using a 555 timer i.c., you would need to use a separate transistor to power the LED's rather than feeding them directly from the output of the 555.

    Have fun!
     
  4. xxdcmast

    Thread Starter New Member

    Nov 18, 2004
    7
    0
    I could have sworn there was an easier way of making an oscillator circuit by using an RC circuit rather than a timer? Does anyone know if Im imagining this or if it can be done only using resistors and capacitors.
     
  5. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    you cannot have an oscillation using only RCs. you still need a transistor to do that. :)
     
  6. Xray

    Well-Known Member

    Nov 21, 2004
    58
    1
    Well, back in the "Old Days" there was a way to make a flashing light using only a resistor, capacitor, and a neon lamp. It is known as a "relaxation Oscillator". It works due to the fact that neon lamps (such as the NE2) have a higher intial ionization voltage (the voltage at which it begins to conduct and produce light) than its voltage when the lamp can no longer conduct and produce light. Many neon lamps were used as equipment pilot lights before LED's came on the scene. You can still buy those little neon lamps at many Radio Shacks. They can not directly replace LED's because they operate at much higher voltage (Typically, at least 85 volts), and they do not produce as much light as today's LED's. You can not make a relaxation oscillator with just an LED and an R/C circuit. BUT, you can buy LED's that have built-in flasher circuits. That would be the simplest way for you to go, but you can not put 10 of them in parallel and expect them to all flash exactly in synch with each other! Eventually, they would all flash at different intervals because of the slight variations in component tolerances.
     
  7. azz

    New Member

    Nov 22, 2004
    1
    0

    Yes there is a way of making an osccillator with resistors and capacitor.See attachment.U have to use two BC108 transistors.This circuit makes each light flash at different times.U can replace one light with a resistor of say 100R.U can change capacitors to speed up or slow down the flashing.Anyway mess around with it. k have fun!
     
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