Now that the Bidirectional LED demo is working but we realized a few problems.
The refresh rate is too slow. It appears that it is taking too much time for the LED to discharge. However this is quite minor, we fixed this by grounding the LED using a resistor.
When we try to extend this to the 8×8 LED Matrix we found a much bigger problem and we are quite clueless as to how to solve it. When we work with the matrix, we are not dealing with a single LED. All the LED are connected to each other by the matrix. The problem is that when a user places a finger on an LED, all the matrix in the entire array is distrubed, so it is almost impossible to determine where the user is touching.
We don’t really have a solution right now but we are thinking about switching to a multitouch surface instead.
Although we have not yet been able to get any useful input from the LED. We bought some LED Marix Display wired them up to the Arduino Stamp. We wrote some firmware code in C and a demo app in Processing. I was hoping to quickly draw a schematic of how the LED Matrix is wired, but I didn’t get to that yet. Hopefully it will be up in the near future. Below is a picture of the 8×8 LED Matrix setup. Each row of the matrix is controlled by a digital I/O pin on the Arduino Stamp. However there is not enough digital I/O on the Arduino Stamp to control the columns, we use a shift register to output data to control the columns on the matrix.
Each circle on the java applet corresponds to a single LED on the display.
Below is also a youtube demonstration of the setup
For those of you that are interested here is the Firmware Source Code in an Arduino Project and here is the Processing Source Code for the GUI as an Eclipse project.
**Note that the RxTxLib included in the GUI source code is strictly for MacOSX
We basically set up our bi-directional LED the circuit according to diagram shown in the last last post. We did followed all the instruction stated the paper on the implementation of a simple bidirectional LED demo, but it just doesn’t work!! There are I think two possibilities why this is not working.
- We did something seriously wrong
- Something is wrong with the microcontroller
At the current moment, I really don’t know how to fix this but here is a picture of the setup followed by the source code
#define digi_fwd 2
#define digi_rev 3void setup(){
Serial.begin(9600);
Serial.println("Arduino");
pinMode(digi_fwd, OUTPUT);
pinMode(digi_rev, OUTPUT);
}
void loop(){
//Emitting
digitalWrite(digi_fwd, HIGH);
digitalWrite(digi_rev, LOW);
//Reverse Bias
digitalWrite(digi_fwd, LOW);
digitalWrite(digi_rev, HIGH);
//Discharge
digitalWrite(digi_rev, LOW);
pinMode(digi_rev, INPUT);
count = 0;
while(digitalRead(digi_rev)){
count++;
}
Serial.println(count, DEC);
pinMode(digi_rev, OUTPUT);
}
The Arduino Sketch can be downloaded here
CREU Project Blog 
