The circuit can be seen in the image above using a breadboard, but to be placed in the case, connections must be soldered directly to take up less space. The question of space used was an important point of the project, I tried to reduce as much as possible the area that Pixie would occupy. Although the case has become small, it is still possible to reduce further, especially by developing an exclusive PCB for this purpose.

Presence detection was done using only one PIR element instead of a complete module such as SR501 or SR505, since the integrated timer and the wide actuation range exceeding five meters were not required. Using only the PIR element the sensitivity decreased and the presence detection is done via software. More details of the connection can be seen here.

Another recurring issue in electronic projects is the battery, there were some possibilities for this project like a 9v battery or a rechargeable one. Although it was more practical, an extra space was going to be needed in the case and I ended up leaving the USB output of the MCU exposed so that the user decides how the power supply will be and making it easier to upload the sketch.

Along with the circuit, a case to accommodate the Pixie components was developed and printed on an Ender 3 Pro using PLA. The STL files were included here.

Some concepts were present during the design of this case:

• Since the plant pot is normally on a table, the display has been placed slightly tilted in order not to lose the viewing area
• Designed to avoid the use of printing supports
• Encourages the exchange of parts for other colors in order to make the product more personalized, interchangeable and fitting design
• The temperature sensor with opening for external environment to enable a more correct reading
• Considering the different pot sizes, the installation of Pixie in the plant can be done in two way
  • Through a rod fixed to the earth; or
  • Using a strap that wraps around the plant pot

Points of improvement

Although functional, there are some points in the design that must be modified, such as the size of the walls that have been defined in order to avoid loss of material and speed up printing during prototyping by 1mm.

The fittings need to be improved by applying the design patterns in 3d printing, probably it will be necessary to adjust the size of the stick and stand fitting in order to snap the pieces correctly.

As a programmer, I can say that it was the most fun part of working, thinking about how to structure and organize the code, took a few hours of planning and the result was quite satisfactory. The fact that most sensors use an analog input generated a separate treatment of the code in order to try to obtain a more accurate reading trying to ignore false positives as much as possible. The diagram above was created with the main blocks of code and it illustrates the core functionality, for more details I recommend taking a look at the code at https://github.com/jnthas/pixie.

There are several points open to modification that allow you to customize Pixie as you wish. Among them I can highlight:

• Sensor reading frequency
• Timeout of expressions
• Max and min temperature, lighting and ground limits as well as the threshold of sensors
• Display light intensity of each expression
• Time between frames of each expression
• The animations are separated from the code allowing you to modify them if you wish

Triggers

It was necessary to implement a way to detect when an action was happening in real time based on the last readings. This was necessary in three known cases, watering, presence and touch, these events should be triggered as soon as a considerable variation of the sensor is detected and for this a different implementation was used. An example of this is the presence sensor, as only the PIR element was used in the analog input, the values read variate often and a logic was necessary to declare that there is presence or not while the temperature sensor, in turn, has a very low variation and just the standard reading of its values is enough to adjust the behavior of the Pixie.