Driving LEDs over 20 inches from uC.

Discussion in 'General Electronics Chat' started by bmurcr, Feb 28, 2012.

  1. bmurcr

    Thread Starter New Member

    Jul 19, 2011
    Here's the setup, I have a uC PCB that is required to turn ON and OFF several remotely located LEDs depending on the input sensor conditions. The problem is that the uC PCB is located a couple of feet away from the LEDs. What is the best way to control a single LED from a uC I/O port that is located some two feet away from the LED? Is it best to locate a transistor or FET near the uC as and then run the long wires to and from the LED pcb? Or should I use some kind of buffer arrangement and then locate the FET or transistor near the LED? Or is it necessary to use an opto coupler or some such arrangement to control the LED? Thanks.
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    Unless you use this in an industrial noisy environment I wouldn't be too concerned about how to do this. I would probably locate a driver transistor near the uC and connect the long wires to the remote LEDs/resistors.

    Everytime you switch a signal on and off on (long) wire try to see the wire as an inductor (that's what it is). This may not be critical for a few mA, but for higher currents it's crucial to do so.
    bmurcr likes this.
  3. #12


    Nov 30, 2010
    LEDs aren't all that special. They're just fairly efficient light bulbs. The issue that I don't know about is the uC. If it is really fast about switching, it could raise a spike or a reflection on a few feet of wire. A small capacitor across the output of the uC should take care of that. Perhaps .1uf.
    bmurcr likes this.