var speed = 6000;
    var nxtMainImg = 1;
    // declare and load main image array
    var mainImgAry = new Array(5);
    for (var i = 0; i < mainImgAry.length; i++){
      eval("mainImgAry[" + i + "] = '/images/home/bg_" + i + ".jpg'");
    }
    
        
    setTimeout("switchMainImg()",speed)
   
    function switchMainImg(){
      var obj = document.getElementById('mainImg');
      obj.src = mainImgAry[nxtMainImg];
  
      if (nxtMainImg == mainImgAry.length - 1){
        nxtMainImg = 0;
      }else{
        nxtMainImg++;
      }

      setTimeout("switchMainImg()",speed)
    }