Week 16:
Interface and Application Programming

Objective

This week I am making a sensor communicate with the computer, which alters the signal and puts out a more complicated visual response.

Software

Practices

 Recap of sensor input

Here are some notes to get back into the frame of mind of Week 11, when the sensor and the board that reads it were made:

 Simple steps to get into Processing

Get a sense of how Processing works by starting with a very basic file from Tiago's page (look at bottom of page).

I had to download "Unarchiver" so I could read Tiago's .rar on a Mac.

Change the serial port specification in Tiago's file:

Connect everything:

See the reading:

Now, load the "Processing Tree" example. Copy and paste the code.

The goal is to change the input for this Processing sketch from being mouse position to being input from a sensor. See the code here ~ there are plenty of comments in the code to explain what's going on.


import processing.serial.*;

Serial myPort;  // Create object from Serial class
int val;      // Data received from the serial port
int sensorData; // Data received from the serial port with 1,2,3,4 framing numbers filtered out
int low=0;
int med=0;
int high=0;
int value=0;
int byte1 = 0;
int byte2 = 0;
int byte3 = 0;
int byte4 = 0;
int value2=0;

////////////////

float theta;

void setup() {
  size(640, 360); // pixel size of output screen
  println(Serial.list());
  myPort = new Serial(this, "/dev/tty.usbserial-FT94S5UT", 9600); // 9600 is baud rate
}

void draw() {
  background(0);
  frameRate(60);

////////////////

  while (myPort.available() > 0) {    // If data is available
    byte1 = byte2; // this byte definition stuff is from Neil's .c code for my TxRx Step Response board; I believe it is "framing" ~ it sets up the port to read cleanly
    byte2 = byte3;
    byte3 = byte4;
    byte4 = low;
    low = high;
    high = myPort.read();

    if ((byte1 == 1) & (byte2 == 2) & (byte3 ==
      3) & (byte4 == 4)) {     // Filter out the framing numbers: 1,2,3,4
      value = (256*high + low) / 100;
      // value =int (map(value, 30000, 57000, 0, 500)); ~ NB, this was a first attempt to change the numbers being read, which were on the order of 50,000 - 60,000. We scrapped this and used simple division instead ~ in the line above, you can see I divided the values by 100.
      println("THE VALUE IS " + value); // print to the screen
    }
  }
////////////////

  stroke(255);
  // Let's pick an angle 0 to 90 degrees based on the mouse position ~ NB, this was changed to a "float" to be reading from the serial port instead of reading from the mouse position
  float a = (value*15 / (float) width) * 90f; // here I added a multiplier for the value, as it made a better range of movement in the visualization
  // Convert it to radians
  theta = radians(a);
  // Start the tree from the bottom of the screen
  translate(width/2, height);
  // Draw a line 120 pixels
  line(0, 0, 0, -120);
  // Move to the end of that line
  translate(0, -120);
  // Start the recursive branching!
  branch(120);
}
void branch(float h) {
  // Each branch will be 2/3rds the size of the previous one
  h *= 0.66;

  // All recursive functions must have an exit condition!!!!
  // Here, ours is when the length of the branch is 2 pixels or less
  if (h > 2) {
    pushMatrix();    // Save the current state of transformation (i.e. where are we now)
    rotate(theta);   // Rotate by theta
    line(0, 0, 0, -h);  // Draw the branch
    translate(0, -h); // Move to the end of the branch
    branch(h);       // Ok, now call myself to draw two new branches!!
    popMatrix();     // Whenever we get back here, we "pop" in order to restore the previous matrix state

    // Repeat the same thing, only branch off to the "left" this time!
    pushMatrix();
    rotate(-theta);
    line(0, 0, 0, -h);
    translate(0, -h);
    branch(h);
    popMatrix();
  }
}

Getting a very jumpy file.

Then changed this line, acc to some advice from Caro:

float a = (value*15 / (float) width) * 90f;

Came up with the number 15 through experimenting.

Watch it working!

See just the screen of Processing:

Files

Some Other Questions About Plant Humidity

Does the reading in a plant pot change if you add water? No. Do rubber gloves work to dampen the signal of the human hand? Yes. But they have to stay totally clean. Does the sensor respond if, while it is in the soil, you touch the plant? Yes. At first. Then no. I'm not sure why. It might have to do with discharge. See what happens with some vegetables on my desk:

So, does this relate to what the capacitance sensor is reading with the plant?

Here's something useful from a website on capacitance sensors:

  The incremental change in the dielectric constant of a capacitive humidity sensor is nearly directly proportional to the relative humidity of the surrounding environment. The change in capacitance is typically 0.2–0.5 pF for a 1% RH change, while the bulk capacitance is between 100 and 500 pF at 50% RH at 25°C. Capacitive sensors are characterized by low temperature coefficient, ability to function at high temperatures (up to 200°C), full recovery from condensation, and reasonable resistance to chemical vapors. The response time ranges from 30 to 60 s for a 63% RH step change.

An Aside: 8-bit vs 10-bit information

Examples where this matter? The way smart beehives work is by using a laser pointer hitting an LDR to send high and low signals. You want to throw out the noise.

For the Python GUI that pops up with my input sensor, the numbers shown correspond to voltage. The resolution of the voltage reading is 5 / 1024 (voltage divided by number of bits available).

See the serial monitor from Arduino that shows the kind of "noise" that can come in through the serial port; so the program is designed to only start reading after 4 consistent bytes come in.

That's essentially it for this week ~~

Other things that happened this week

 Vailets Hack Day.

Lots of kids exploring design and tech! Thanks to Xavi Dominguez.

The kid on the right was really into all of it; he just happens to look like a gang banger. He was charming.

Had frustrations trying to set up a Kinect scanner (XBox 360) to work with Skanect 1.5.0. Tangentially related to Week 05.

Great difficulty getting Skanect to recognize the sensor ~ it happened occasionally, but I couldn't tell why sometimes it worked and sometimes not. Switched to Windows, tried 4 different drivers. Seemed to work with 2.0. Deleted other drivers. Physically moved location. Didn't work. Returned to former location. Worked. Tried again to move. Didn't work. Does this have to do with the quality or consistency of the power? It is hard to know. The software + hardware speak to each other only very begrudgingly.

 Recitation: Gian Paolo Bassi of SolidWorks