Simpler, smaller LED sensor project

[dalewheat]

justDIY,

Instead of using the AtoD conversion to read the value of the LED sensor, couldn't you use a digital input and measure the time to discharge the junction charge?  I'm trying to build the simplest possible version of this device, more or less just to demonstrate the idea.  Ideally, I'd like to be able to use two LEDs as a one-dimensional slider control.

Here's the background information for the LED sensor project as started by justDIY:

http://www.merl.com/publications/TR2003-035

Thanks,

Dale

[justDIY]

In a sense, that's all I'm doing with the A2D sample ... transfer the charge from the junction to the internal sample capacitor, and then timing how long it takes to discharge that capacitor.  the time value is just correlated to a voltage value.  the language I'm using (along with the microcontroller I've chosen) provides a simple interface to the A2D functions, so its easy for me to use that method, rather than setting up a subroutine to time the transistion from high to low on a digital input pin... thats not a bad idea to try out, since it might allow for a faster 'reading' of the sensor

I have observed it takes a fair amount of time for the voltage stored in the junction to discharge, the intensity of light reflected onto the junction just doesn't drive it down very fast.   I've settled on 600uS  for the 'sampling' period in my a2d routines - it works pretty well under 'normal' room light, and exceptionally well in a 'darkened' room... I think the reason this technology is not 'in use' is daylight screws it up pretty bad - so do 'strong' indoor lights, like a halogen floodlight I have over my smd workarea.

I will dig up some of my 'proof of concept' code, before I started going crazy with trying to built huge arrays - it's in basic, but its so darn simple you should pick it up right away.

[justDIY]

Attached is a text file with my basic code for the led sensors.

there is a lot of stuff in the beginning that's just junk I carry from project to project, mostly just stuff setup for my breadboards.

This code reads four led sensors and outputs the results to an attached vfd I use for debugging.