LDR SENSITIVITY MEASUREMENT USING PARALLEL PORT
This tutorial is taken from the book MY EXPERIENCE IN PARALLEL PORT INTERFACING. you can download it free from the files section(file:-parallelport(3 files) of yahoo group-booksbybibin http://groups.yahoo.com/group/booksbybibin/ comments about this book on www.booksbybibin.blogspot.com LDR SENSITIVITY MEASUREMENT How to measure the sensitivity of an LDR?????? I thought of using ADC to measure and see the time difference between three consecutive different reading. I can't say this method is ideal, but this method can somehow measure the sensitivity to an extent. By this method i got sensitivity around 3ms, but I have seen that LDR sensitivity is around 10ms. Anyway this circuit can be used to read LDR output in digital format. #include"bparlib.c" #define ChipSelect Clear_ControlPort_bit(0) // to clear RD' and CS' int Read_adc(void); void main() { float a=1,b; int i=0; for( i=0;i<400;i++) { b=Read_adc(); printf("\nadc output:%f\n",b); a= b*5/255; //conversion supply voltage is 5V printf("the input voltage is %f",a); }} int Read_adc(void) { ChipSelect; //to select the chip, enabled delay(1); Clear_ControlPort_bit(1); delay(1); Set_ControlPort_bit(1); delay(1); return(Read_DataPort()); } read the LDR 400 times continously and take the least count in which consecutive 3 readings will differ. You can use this circuit to change the parameters of your computer monitor so that you will feel same effect with variation in external light.

Firstly output of LDR is analog. Suppose if you want to measure velocity of a car, place the sensors some fixed distance(let it be some constant) apart and the difference b/w time of crosssing of car will give the time. For getting speed =constant distance/time But here it is 38Khz+TSOP(it is digital output). Then it is connected to parallel port and it have range about 1m. But LDR have max upto 3-4cm. So this will surely be TSOP