Does anyone here know Electronics?
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Thread: Does anyone here know Electronics?

  1. #1
    Über Genius First opel 1981's Avatar
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    Does anyone here know Electronics?

    I am in need of someone to explaint to me, in "idiots" terms, how to use a 5v source to trigger 12+v.

    It needs to be faster than a relay as I want to trigger a BIG LED with Pulse Width Modulation.

    I know how to use a MOSFET to trigger a ground on a supplied positive voltage but not to trigger a positive voltage to a passive ground.

    Make sense?
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    Humans are not an endangered species!
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  3. #2
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    Common collector - Wikipedia, the free encyclopedia. Put your current limiting resistor and LED between the emitter leg and ground. FYI the LED and resistor will see 12v - 1 diode drop (12v-~.7V). Your 5V applied to the base of the transistor will switch = ~11.3V to your led and current limiting resistor.

  4. #3
    Über Genius First opel 1981's Avatar
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    Like this?

    LEDrev1.jpg
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    Humans are not an endangered species!
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    Close- more like this



    Quote Originally Posted by First opel 1981 View Post
    Like this?

    LEDrev1.jpg
    Attached Images Attached Images

  7. #5
    Detroit,where my home was 2 Fast 4 U's Avatar
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    you could put the resistor between the +12V and the collector, instead of between the emitter and the led.
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  8. #6
    Über Genius First opel 1981's Avatar
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    Thanks guys.

    I can adjust the input from the +5 but having the resistor won't hurt anything so it's good to put it there.
    My LED is built for 12V (an automotive LED) with some sort of internal resistance. But that might cause problems all by itself with the PWM because I have no idea how the LED is internally configured. Testing will figure that one out.

    Wherever I don't need PWM I will just be using relays.

    Does anyone have any of that magic smoke stuff that's in electronic components? I know I'm going to end up venting a bit.
    Opel GTs are not GM products
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    Humans are not an endangered species!
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    If the LED is designed for 12V then leave out the Led current limiting resistor. But do use the base current limiting resistor.

    Also- why are you PWM'ing the LED? It looks like it is designed for continuous operation. PWM is sometimes used to overdrive the LED current for short duty cycles for higher brightness but many times LED arrays (like in a taillight) are scanned so that to the human eye they appear to be on constantly but in reality are pulsed at a particular frequency and duty cycles so as to have an "off" period to save power.

    ???

    Quote Originally Posted by First opel 1981 View Post
    Thanks guys.

    I can adjust the input from the +5 but having the resistor won't hurt anything so it's good to put it there.
    My LED is built for 12V (an automotive LED) with some sort of internal resistance. But that might cause problems all by itself with the PWM because I have no idea how the LED is internally configured. Testing will figure that one out.

    Wherever I don't need PWM I will just be using relays.

    Does anyone have any of that magic smoke stuff that's in electronic components? I know I'm going to end up venting a bit.

  10. #8
    Über Genius First opel 1981's Avatar
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    Quote Originally Posted by Nathan Acree View Post
    If the LED is designed for 12V then leave out the Led current limiting resistor. But do use the base current limiting resistor.

    Also- why are you PWM'ing the LED? It looks like it is designed for continuous operation. PWM is sometimes used to overdrive the LED current for short duty cycles for higher brightness but many times LED arrays (like in a taillight) are scanned so that to the human eye they appear to be on constantly but in reality are pulsed at a particular frequency and duty cycles so as to have an "off" period to save power.

    ???
    The reason I want to PWM the LED is to have it on in the high state to be a brake light but in a PWM state to dim as a running light. I know there are many ways of accomplishing this but I'm playing around with Arduino and want to see if it will work so I can have single wire, multi brightness, lighting.
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    Humans are not an endangered species!
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  11. #9
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    Quote Originally Posted by First opel 1981 View Post
    The reason I want to PWM the LED is to have it on in the high state to be a brake light but in a PWM state to dim as a running light. I know there are many ways of accomplishing this but I'm playing around with Arduino and want to see if it will work so I can have single wire, multi brightness, lighting.
    Ahh OK- very cool. I have bunch of Arduinos of various types around my workbench- they are a great way to learn/use microcontrollers without all the hassles of setting up a development environment. BTW from what I can tell there is no reason you have to switch the positive side of the led for your PWM scheme- look into an open collector configuration (basically move the LED up into the collector with the negative side of the led connected to the collector and the positive side to +12VDC). Your 5VDC PWM signal from the Arduino will still work exactly the same way.

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