The principle is very simple : The microcontroller powered by a CR2032 cell through a reed switch (activated by a magnetic field) is connected to a LED situated in the center of the flower. The microcontroller blinks the LED which transmits a Morse code message hardcoded in its firmware
In order to make the blinking smooth, the intensity of the LED is progressively changed through pulse width modulation (PWM)
The microcontroller is a MSP430G2211 from TI. It is one of the two chips delivered with the MSP430 Launchpad development platform, which makes it very affordable and easy to program through a USB connection. But any other simple microcontroller can be used for this project provided it has at least one digital output capable of powering a LED.
The electronic circuit is placed inside the flower pot, the flower is activated by approaching a magnet. The magnet could also be hidden in an element of the decor of the flower to make it more discrete (I did not do it).