Final result:

When people touches the terrarium, the Leds start to blink mimicking living creatures breathing; a blue leaf slowly appears in the sand.

My target audiences are people who would like to appreciate unnoticeable beauty. I invite my audiences to observe all the common electronic components closely and enjoy the authentic and magical feeling of technology.

In this final version, I used Attiny instead of Arduino to save space. I also used a lot of colorful wires to create a messy, organic feeling.

To give a better control over the batteries, I used a battery holder of the coin battery and a detachable wire for the 9V battery.

For further iterations, I would like to explore the possibility of a  larger scale and adding projection to it as Sheena form Parsons Paris suggested. I made another project called Grow that explores the connection between physical and digital world that related to Sheena’s comment. In this iteration I only used physical components because comparing to virtual images, people consider the physical components less authentic.

After fill in the sand, I found the touch sensing became less sensitive as before. I believe the resistance of the sand affected the sensing. But I already soldered the Attiny in the circuit so I can’t change the code to sense higher input.

Here is the Instructable post.