Our local instructor for this week is Iván Sánchez. This week we need to design and build a used interface for our input/output boards. I was thinking to use Three.js with Node.js. But finally, I have decided to go and use Processing, for three reasons:

  • I have not used it before
  • I know to build UIs, but I need want to understand better the communication with the boards
  • I would like to be able to use the in and out boards with the same UI, so I prefer to focus in this
Processing is a Java based programming language that, as themselves say "Processing is a flexible software sketchbook and a language for learning how to code within the context of the visual arts".

To Do

  1. UI for getting data from a board to the computer
  2. UI for sending data to a board from the computer
  3. Group work

The "Doing"

UI for getting data from a board to the computer

My board for input week assignment is a HALL Effect sensor. I want to be able to make a representation of the analog data got from that sensor. So, my plan is to follow the next steps:
  • Start getting data from serial
  • Then, Print the data in processing
  • And then, Do something with the data in processing
To get the data from serial I downloaded (a recommendation from Bas Withagen ) CoolTerm, a nice serial port terminal application that allows to see hex data.
Then, I used Neil's code (putchar function and preamble) to send data to the serial port from ATtiny44. Putchar sends a byte with start and stop bits. Then, before sending the value from the sensor, we need to send a preamble, so the receiver would know which are the two bytes that are data. So, each time the code enter the main loop , I check if there are new values from the sensor and then send them with a preamble of 4 bytes (1,2,3,4): 3d object design
CoolTerm showed something, good! 3d object design
Then I moved to processing. Processing is quite straight forward to use, as it looks. Things you need for a simple program printing for serial communication:
  • define the variables
    • The serial port number can be found in Device manager and also in CoolTerm
  • implement the setup() method
    • This method is executed once when the program starts
    • The serial port number can be found also from the list, although I do not use that
    • create the serial object
  • implement the serialEvent(Serial p) method
    • This method is called each time some data is detected in the serial port
    • We read the serial input knowing how the serial output works (serial transmission from ATtiny44 described above)
  • implement the draw() method
    • The draw method is continuously called by processing any time there are changes. This behavior could be canceled with noLoop(). But my UI is going to be dynamic, so I leave it as it is
3d object design
With this, I could check the values I was getting from the sensor:
  • values between 0 and 512 for one side of the magnet getting closer
  • values between 512 ans 1023 for the other side of the magnet getting closer
Then, I decided on my UI (See picture below) :
  • A smiley face. The mouth size corresponds to the Hall Effect sensor values in real world.
    • Static face drawing found in Google (see Resources section section). That code is for static smilie face. I would implement the code to vary the mouth size
  • Mouth gets bigger if candy gets closer. The candy represents one side of a magnet in real world.
    • Lollipop image found in Google with CC license (see Files section)
  • Mouth gets smaller if fish-bones get closer. The fish-bones represent the other side of a magnet in real world.
Which translates into code as
  • circle in the center with two ellipses (as eyes) and an arc with variable height to open/close the mouth according to hall effect data
  • A picture of a candy and fish-bones that will move towards the mouth according to hall effect data
The image for the UI:

3d object design
Each element of the image has it's own draw method that I call in the implemented draw()

3d object design
Each time a new value is received, in the serialEvent I call an updateData function that calculates the values for the X, Y positions of the images, according to the measurement received.

3d object design
And these are the different results according with the magnet movement:

3d object design
Magnet gets close on one side
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Magnet gets close on the other side
And now, make it a "bit" real world :
  • I print the lollipop and fish-bones images, stick them together and put the magnet inside
  • I create Pepe, a paper man with a big mouth, and I put inside the Hall Effect magnet
Meet Pepe:

3d object design
Pepe does not like fish-bones
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Pepe does like candy

UI for week 10 in FabAcademy from Marta on Vimeo.

UI for sending data to a board from the computer

My initial idea is to read a mouse event in processing and send some data accordingly to the board from assignment13 output board which was a charlieplexing. I wanted to light control the LEDs with the computer. But for starting, I would just use a board with a LED.
I have decided to read the data from serial in the ATtiny as one example I´ve found from Neil: a pin interruption, as I wanted to test interruptions. After modifying Neils code, (as I have a loop for sending hall effect sensor data to the computer that gets interrupted when receiving data from computer) to my own board, I have managed to make it work, but not completely:
  • I managed to have the serial output working as described above: sending data in C ATtiny44 main loop
  • I manage to handle a click event from the mouse in Processing
  • I write to the serial port in Processing
  • 3d object design
    Processing code
  • I read the data in the ATtiny44 with getchar() from Neil in an interruption
    • I change a LED state with the information I get, as seen in the Interruption code
  • 3d object design
    Pins definition
    3d object design
    set the pin changed interruption in main before the loop
    3d object design
    Interruption code: pin on/off depending on received data
So although I can change the LED state several times (on-off with mouse clicks), at some point I stop receiving data in the computer from the HALL Effect sensor... and then also I cannot change the LED with the mouse. It seems to me I am getting into some kind of loop in the code it cannot recover from. I would like to come back to this in the future. But at this point, I do not know the problem.
In any case, I would try to isolate the problem, starting from removing the reading data loop from the interruption code. That is, react to the fact I am receiving data, and do not read the actual data. And see what it happens.


Once done


  • I have implemented a serial output for my IN board
  • I have implemented a serial input for my OUT board
  • I have implemented a serial input in the computer with Processing
  • I have implemented a serial output in the computer with Processing
  • I have implemented a UI for the communication
    • INPUT: A drawing changes gradually with the input serial values
    • OUTPUT: A LED is switched on/off with each mouse click event


  • As every week, lack of time.
  • I cannot identify the problem with my interruption in the Code in the ATtiny44. I plan to come back to this, proceeding as described in the text to try to isolate the problem.


  • I have "learnt" how to implement interruptions in C for the ATTiny
  • I may need to add a "pending" section, for those things not mandatory but that would be nice to have


  • CoolTerm is a very nice serial terminal!