Hex Inverter for LEDs

Discussion in 'General Electronics Chat' started by DanRilley, Dec 21, 2009.

  1. DanRilley

    Thread Starter Senior Member

    Jan 13, 2008
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    Hi, I am using an Arduino pin to light an LED, very basic. I have a few spaces on a 74HC14 chip open and am wondering if it's best to power the LED by buffering it through the Hex Inverter, or just straight out of the microcontroller?

    The reason I ask is that I recently saw a schematic that had an LED powered through two NOT gates of a Hex Inverter and I was wondering if its better for power consumption or something. But maybe it's totally unnecessary, I know I can just set the microcontroller pin to LOW and then connect an led and a resistor to +V and it will work.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    It's always a good idea to refer to a datasheet.
    Here's a 74HC14 datasheet: http://focus.ti.com/lit/ds/symlink/cd74hc14.pdf
    Note that TI's spec for absolute maximum spec is +/-25mA per pin, +/-50mA to Vcc/GND. It is best to stay well below absolute maximums.

    You will need to consult your Arduino datasheet to determine it's limits per I/O pin and total package limits.
     
  3. DanRilley

    Thread Starter Senior Member

    Jan 13, 2008
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    I think the current is fine, the LED only takes 20ma I think. My question is, is there any big difference between going straight out of the Arduino (40ma/pin FYI) to an LED, or to go from the arduino, through the 74HC14 to the LED, is there any advantage to the latter?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Ask yourself which component would you rather have to replace? ;)

    As an aside, it's a good idea to use current limiting resistors on your uC I/O pins, just in case a component the uC is connected to fails by shorting to one of the rails. This helps to prevent a "domino effect" of one component failing causing multiple failures.
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    It is always a good idea to use buffers as protective measures. I do not know much about your board. But I guess it use SMD components. Sometimes not so easy to change for the hobbyist. So if you use external buffers you can replace they will be fried not your board.
     
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