Electronic – arduino – the proper and up to date method for multiplexing digital inputs

arduinomultiplexer

So Im following the diagram here for wiring up a MC14067BCP:
http://fluidforms.eu/docs/MultiplexedArduinoWiringDiagram.pdf

The only difference being that I am doing one set of 16 sensors and not four. Additionally, my sensors are 5k – 250k LDRs (light sensitive resistors) that I have connected to ground on the end opposite of those connected to the connections shown in the diagram above.

When I run my sketch, the serial line shows output that is similar to what would be shown if no wires were connected to my analog in at all. (see the question here to see what I mean by that: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1238854387) This is really stressing me out and it would be amazing if someone could enlighten me as to what is going on.

Here is my code:

int CONTROLpin1 = 2;
int CONTROLpin2 = 3;
int CONTROLpin3 = 4;
int CONTROLpin4 = 5;
int analogPin = 0;


// Variables:
int actualSensorValue = 0;             // value from the analog input


void sendCommand(int value) {
  Serial.println(value);
}


void setup() {
  //  set the states of the I/O pins:
  pinMode(CONTROLpin1, OUTPUT);
  pinMode(CONTROLpin2, OUTPUT);
  pinMode(CONTROLpin3, OUTPUT);
  pinMode(CONTROLpin4, OUTPUT);
  pinMode(analogPin, INPUT); 

  Serial.begin(9600);
}


void loop() {
  int i;
  for (i=0; i <16; i++) {

    // set control pins on the multiplexers
    digitalWrite(CONTROLpin1, bitRead(i,0));//bit4
    digitalWrite(CONTROLpin2, bitRead(i,1));//bit3
    digitalWrite(CONTROLpin3, bitRead(i,2));//bit2
    digitalWrite(CONTROLpin4, bitRead(i,3));//bit1


    Serial.println(i); // print which pin we are on
    actualSensorValue = analogRead(analogPin);
    sendCommand(actualSensorValue);


    delay(1000); 
  }
}

Additionally, I have tried cutting it down to the bare minimum and only wiring up a single sensor. When looking at the output, there appears to be no change.
Here is a picture of the bare bones wiring:

picture

(but to be clear my end goal is still the diagram at the top of this post).

Best Answer

To do "multiplexing" you'd need some way to control the select line of the mux (which means an extra log base 2 inputs according to the number of sensors you have, so for 16 sensors you'd need four more outputs to control the select line). And you'd need a bunch of AND gates to select which mux channel you want to connect to the inputs.

If they had CS (Chip Select) pins themselves, you could avoid the gates. But you still have to worry about converting 4 outputs into 16 chip selects; could probably get a 4-bit decoder to do that.

I don't like any of those solutions, though. They're very messy. Personally, I would use a couple I2C input buffers and then wire all the inputs to those and then read the buffers with the Arduino. Easier to handle, and only uses two inputs on the Arduino. Easily extensible too, so long as you don't have any address conflicts.

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