---

Lousa mágica & Lousa paramétrica

(versão em Português)

Tools for drawing with potentiometers (take a look at the GitHub repo!)

Lousa mágica is something like “magic blackboard”, it was the name in Portuguese of the “Etch A Sketch” drawing toy that inspired this project. Then Lousa paramétrica would mean something like “parametric drawing board”.

Brief history

Lousa mágica video at Sesc 24 de maio - credits: João Adriano Freitas

• Lousa mágica was inititally presented as part of Estúdio Hacker activities at the inauguration of Sesc 24 de Maio, on August 2017 (video above). It used 6 potentiometers for drawing and drawings could be erased by tilting the control box.

It was also possible to post tweets with the drawing content (using a Twitter API library).

• On Estúdio Hacker Day (September 7th, 2017), also at Sesc 24 de maio, a workshop was held where the participants set up a version of Lousa mágica with 4 potentiometers in a breadboard.

• Setups with 4 potentiometers using a variation of the Lousa mágica software and a new version called Lousa paramétrica with a recursive parametric drawing of a tree were displayed at the Sesc Art Circuit 2018.

• Several sketch-a-day project drawings were made to be used with the same setup.

• TO DO: Add links to other 'parametric' drawings that can be modified with pots

Setup instructions

Materials

• Arduino (or similar board) with at least 4 analog pins;
• USB cable to link up the Arduino to the computer;
• 4 to 6 linear 10kΩ potentiometers (type “B”) (you can use 2 or 3 but it’s not as cool);
• A breadboard and some jumpers;
• A computer with a display (or a laptop) running Linux, Mac or Windows. Use a big TV or a projector for bigger impact on guests!
• Optional: button or mercury tilt switch (the computer keyboard may be used instead) and 10kΩ resistor (if it’s a button/switch connected to a pin other than D13);

1. Download and install the Arduino IDE;

2. Connect your Arduino/board to your computer, open the Arduino IDE, and in the menu File > Examples > Firmata look for the sketch called Firmata All Inputs. Next, select your board’s model in Tools > Board: , and in Tools > Port, the USB/serial port the board is connected to. Lastly, click the ➔ button to upload the sketch to the board;

   Known problems:

   • Some Arduino clones need a special USB driver: How to Install CH340 Drivers
   • If you use Linux, you might not have permission to access the USB/serial port, that can be corrected by typing sudo usermod -a -G dialout <your username> in your shell prompt.

3. Connect each potentiometer to your Arduino/board according to the image:

   4.1 Connect the side terminals of each potentiometer to the 5V e GND pins,

   4.2 Connect the central terminals to the board’s analog pins: A1, A2, A3 e A4;

4. Optionally, if you chose to use a button/switch to erase the drawing in Lousa mágica, it must be connected to the Digital 13 pin and 5V pin;

   If not using the D13 pin, connect the chosen pin terminal to the 10kΩ resistor (so called pull-down resistor) and to the GND pin simultaneously. The D13 has a built-in pull-down

5. Now the software part, for drawing in the screen:

   5.A To use with Thonny IDE, py5 and pyfirmata

   • Install Thonny and the thonny-py5mode plug-in;
   • Inside Thonny IDE, select Tools > Manage Packages... and install pyFirmata;
   • Copy code from:
     • LousaMagica_py5.py - Drawing with pots
     • lousa_parametrica_arvore_py5.py - Parametric recursive tree

   5.A To use in the Processing IDE:

   • Open the Processing IDE and download the Arduino (Firmata) library in Sketch > Import Library... > Add Library...;
   • Copy code from sketches made for Processing Java Mode;
   • Sketches made for Processing Python Mode (not currently working due to Python mode + Serial library issues).

Arduino Nano example

Definitive setup suggestions

• Tools: pliers and soldering iron;
• Use a tilt switch (mercury switch) instead of a button on D13 to erase drawings in Lousa mágica.
• Setup in a box with a transparent panel, with holes for the potentiometers.

Other ideas

• Pong with potentiometers, Dojo version: github.com/arteprog/cursos/tree/master/DOJO-pong-com-pot
• “Wireless” version made by João Adriano Freitas: github.com/jaafreitas/LousaMagica

---

Alexandre B A Villares (abav.lugaralgum.com), CC-BY-NC-SA-4.0 License Translated by Carolina Giorno