How do you disable a Timer?

How do you disable a Timer ?
When you set it to null, it keeps firing. And at some strange interval !

        private Timer _Off_Timer;

        public LCD_Backlight()
            _GPIO_LED = GpioController.GetDefault().OpenPin(Hardware.LCD_BackLight_Pin);

        public void On()
            _Off_Timer = new Timer(Timer_Elapsed, null, 

        private void Timer_Elapsed(object state)
            _Off_Timer = null;

how about:


Yeppers !!
That worked. Thanks!

Looks like this works too