what is the unit of Light dependent resistor (LDR)?

[sunnystar]

my 3 questions:
1)what is the unit of Light dependent resistor (LDR)? lux or resistance??
2)somebody have set in c code that if its value exceeds 50 than the buzzer turns on, wot is that 50? it's resistance or light or wot??
the code lines are:

avg.smoke_level=(sum.smoke_level/10)/10.24;
if(avg.smoke_level<=50 )
{
 output_low(PIN_D2);
}
else
{
output_high(PIN_D2);
}
   delay_ms(500);
   }

3) dividing by ten bcoz 10 samples were taken, but wot's the reason of dividing by 10.24??

 

[yassin.kraouch]

my 3 questions:
1)what is the unit of Light dependent resistor (LDR)? lux or resistance??
2)somebody have set in c code that if its value exceeds 50 than the buzzer turns on, wot is that 50? it's resistance or light or wot??
the code lines are:

avg.smoke_level=(sum.smoke_level/10)/10.24;
if(avg.smoke_level<=50 )
{
 output_low(PIN_D2);
}
else
{
output_high(PIN_D2);
}
   delay_ms(500);
   }

3) dividing by ten bcoz 10 samples were taken, but wot's the reason of dividing by 10.24??

are you sure that you are talking about LDR ?
because if i see smoke level, i have the feeling that this is a smoke detector,
the unit of LDR is OHM, because its a resistance, and its value vary with the QTY of light it receive,

 

[sunnystar]

yes, LDR is used as a smoke detector.

 

[paulfjujo]

hello


LDR Light dependant resistor
the value depend of the light (Lux)
could be maybe > 100K ohms in the dark and <10K in the light day..
Used in voltage divider..
ex: +5V --- R=100K ---- junction -----LDR ---- 0V
ADC input link to the junction point ...
so you get a few voltage in the dark (so few points of ADC measure)
and maximum voltage in light (so tend to 1024 point of ADC measure)

the raw measure seem to be the result of ADC conversion 10 bits..

ADC 10 bits => 1024 points..
if the mesure is 1024 (maximum scale) divide by 10.24 => 100 => 100% full scale
so if the threshold is 50 => 50%


nota: be carefull when using floating point values , mixed with integer ..problemo..