Week 16

Interface and application programming.

Interface and application programming

For this week i'm going to interface a capacitive touch sesnor with my computer.

Part 1:

Device interface overview

The board uses serial interface to send the data of 4 sensors to the computer using FTDI cable. The data formatted as in the following:

0b0000DCBA

Where A is the value of sensor one, B is the value of sensor two, C is the value of sensor three, and D is the value of sensor four. The value is 1 if the sensor is touched or 0 if not. For example if sensor 1 is touched, the value recieved will be 1, and if sensor 4 is touched, the value will be 8. If multiple sensors is touched, the value recieved will be the sum of the value of the two sensors.

Interfacing

I used TKinter on python to communicate with the board and display the touched plates. I used Neil's code as a base and developed my interface.

The first part of the code is imorting the modules, and set some variables that define the window size and colors ,, etc.

from Tkinter import *
import serial

lastByte = 0

WINDOW = 800 # window size

squaresNumber = 4

tsquare = WINDOW / (squaresNumber + (squaresNumber - 1) + 2) #square size

tsquareColor = '#d6d6c2'
tsquareColor_active = '#000033'
backgroundColor = '#7a7a52'

The idle function is the routine where i read the serial, check if the sensor is touched, and update the graphics. After reading the value, i perfome logical AND on the sensor bit position and shift it to the 0 bit. So no matter the sensor's number, when it is touched the value of its variable will be 1. Finally i loop over the sensors and change the colors based on the value, then update the canvas.

def idle(parent,canvas):
   #
   # idle routine
   #
   global tsquareColor
   global tsquareColor_active

   ser.flush()
   sbyte = ord(ser.read())
   touchSensors = [(sbyte & 1,'rect1'), ((sbyte & 2) >> 1, 'rect2'), ((sbyte & 4) >> 2, 'rect3'), ((sbyte & 8) >> 3, 'rect4')]
   for x, n in touchSensors:
        if x == 1:
           canvas.itemconfigure(n, fill=tsquareColor_active)
        else:
           canvas.itemconfigure(n, fill=tsquareColor)

   canvas.update()
   parent.after_idle(idle,parent,canvas)

The rest of the code is to setup the canvas, create the rectangles, and setup the serial communication.

Download the source code:

TouchsensorGUI.py

Fab Academy - Week 11 - Input devices from Mohamed Kamel on Vimeo.

Part 2:

This time i'm going to use the board as a mouse to scroll up and down when i touch the plate in different directions. I found a tutorial that helped me get started. So this time i'm going to read the data from the serial port as before but i'm making some anlaysis on the data to detect the order of touching the plates and use pyautogui library to automate a scroll up or down.