cambo,
Here is a post I did on the Arduino forum regarding signal processing:
I have built a simple shield to clean up the signal from the IR sensor. It uses a TLC3702CP push-pull comparator to give a nice clean 0 - 5 vdc square wave signal. The comparator eliminates any problems due to background light changes. I set the trigger at 3 volts so anything below 3 volts gives a 0 volt signal and anything above results in a 5 volt signal. The comparator is not entirely neccessary but makes the system more robust. I am new to the Eagle program but tried to put together a schematic:
Edit: If you use 3.3 volts for VDD you do not need the R2 voltage divider.
I have been using a Dane Elec SD card with the script without problems but when I started making changes to the script, I started getting errors. The Fat16 author does not recommend Dane Elec so I tried a Kingston card and the script started working properly. See the Readme.txt file in the Fat16 documentation for more info.
I am working on a sketch that uses the Fat16 and messenger libraries to write data from the serial port to the SD card. I will be posting it on the Arduino forum so I do not hijack this thread any further.