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[on:]

So, I wanted to push this tutorial to its limits, making 16 touch sensors (I'm using screws for that)

http://www.arduino.cc/playground/Code/CapacitiveSensor

And using a 16 channel analog multiplexer (this is the one I actually tested with)

https://www.sparkfun.com/products/299

So far so good, it works. But I just want to double check things out, to be sure it won't burn something after hours of usage. ;-)

Here's the test code I created, I'm just using an Arduino UNO + the multiplexer, nothing else. Thanks for any advice! 

Code:

#include "pins_arduino.h" // Arduino pre-1.0 needs this
volatile uint8_t* port;
volatile uint8_t* ddr;
volatile uint8_t* pin;
byte bitmask;
#define pinToMeasure 8
uint8_t values[16] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 };
uint8_t buttons[16] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 };
uint8_t buttonEvent[16] = { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 }; // 1 == normal push, 2 == hold push //
char printOut[16*2];
uint8_t counterIdle = 0;
#define oversample 8
#define sensitivity (4*oversample)

void setup()
{
  for (char x=2; x<12; x++) pinMode(x, OUTPUT);
  for (char x=2; x<12; x++) digitalWrite(x, LOW);
  Serial.begin(9600);
 
  port = portOutputRegister(digitalPinToPort(pinToMeasure));
  ddr = portModeRegister(digitalPinToPort(pinToMeasure));
  bitmask = digitalPinToBitMask(pinToMeasure);
  pin = portInputRegister(digitalPinToPort(pinToMeasure));
}

void loop()
{
  memset(values, 0, sizeof(values));
  for (uint8_t y=0; y<oversample; y++)
  {
    for (uint8_t x=0; x<16; x++)
    {
      digitalWrite(2, bitRead(x,0)); digitalWrite(3, bitRead(x,1));
      digitalWrite(4, bitRead(x,2)); digitalWrite(5, bitRead(x,3));
     
      values[x] += readCapacitivePin();
    }
  }

  uint8_t buttonchanged = 0;
  for (uint8_t x=0; x<16; x++)
  {   
    if (values[x] <= (sensitivity/2) && buttons[x] > 0)
    {
      if (buttons[x] < 99) { buttonEvent[x] = 1; buttonchanged = 1;  }
      buttons[x] = 0;
    }
    else if (values[x] > sensitivity && buttons[x] < 120)
    {
      buttons[x]++;
      if (buttons[x] == 99) { buttonEvent[x] = 2; buttonchanged = 1; }
    }
  }
 
  if (buttonchanged)
  {
    Serial.print(":");
    for (uint8_t x=0; x<16; x++)
    {
      if (buttonEvent[x] == 1) Serial.print("#:");
        else if (buttonEvent[x] == 2) Serial.print("@:");
        else Serial.print("_:");

        buttonEvent[x] = 0;
    }
    Serial.println("");
    counterIdle = 0;
  }
 
  counterIdle++;
  if (counterIdle > 100)
  {
    Serial.println("");
    counterIdle = 0;
  }
}


uint8_t readCapacitivePin()
{
  *ddr &= ~(bitmask); // Make the pin an input with the internal pull-up on
  *port |= bitmask;
  uint8_t cycles = 6;
  for(uint8_t i = 0; i < 6  ; i++)  // Now see how long the pin to get pulled up
  {
    if (*pin & bitmask){ cycles = i; break; }
  }
   
  *port &= ~(bitmask); // Discharge the pin again by setting it low and output
  *ddr  |= bitmask;

  return cycles;
}

[Reply #1 on:]

Code:

volatile uint8_t* port;
volatile uint8_t* ddr;
volatile uint8_t* pin;

Why are these volatile? Are you expecting the values to change, in an interrupt, after being set in setup()?

I don't see your code using interrupts.

Code:

    for (uint8_t x=0; x<16; x++)
    {
      digitalWrite(2, bitRead(x,0)); digitalWrite(3, bitRead(x,1));
      digitalWrite(4, bitRead(x,2)); digitalWrite(5, bitRead(x,3));
     
      values[x] += readCapacitivePin();
    }

I don't see the value of multiple statements on one line. It makes the code much harder to read.

Code:

      if (buttons[x] == 99) { buttonEvent[x] = 2; buttonchanged = 1; }

Ditto here (and other places). What is the magic value 99 for? A #define with a meaningful name would be better.

[Reply #2 on:]

I'm interested in knowing how this works out!

What are you mounting the screws to?  What are you planning for the sensors to control?

Good luck!

[Reply #3 on:]

Well, I will be building the prototype soon, it will handle 16 ultra bright LEDs, so one sensor per LED. I will check some nice screws this week, to see something I like. ;-) Once I have something nicer to show, I will post pictures.

[Reply #4 on:]

I was thinking about doing the same thing, but instead of LED's I'm going to be switching relays.

Please keep us all posted!