[moved] ldr to lux conversion code in altera

[cjcg]

Hello. I'm an ECE student. Anyone here who knows the LDR to lux conversion code in altera? This for our project. Thankyou

I hope you can help me

 

[vGoodtimes]

For reference:
https://www.edaboard.com/threads/278855/

I[lux] = 10000 / (R[kΩ]*10)^(4/3)

this probably would be done in a CPU. the cube root and division can be problematic.

 

[cjcg]

Thank you. But how about the code in or circuit diagram in quartus?

 

[c_mitra]

I[lux] = 10000 / (R[kΩ]*10)^(4/3).

Obviously this is wrong. This is not dimensionally correct. Further, various LDR can be of different resistance under the same light.

 

[vGoodtimes]

Obviously this is wrong. This is not dimensionally correct. Further, various LDR can be of different resistance under the same light.

Ok, I don't do anything with LDR. I just assumed this was a curve fitting approximation and didn't care about the units because curve-fitting is all about ignoring the absurd units.

 

[FvM]

Assuming a constant slope in double logarithmic R versus illumination plot is just a simplification. In contrast to the 0.75 slope given by vGoodtimes, I see "gamma" numbers of 0.8 to 0.95 for PE/Excelitas photocells.

Real LDR photocells have more or less bent curves in the double logarithmic plot. There's also a large type variation, as mentioned by c_mitra.



Presume this is rather an academic exercise problem than a real instrument design. My general approach would be an empirical calibration table with interpolation. Implement the table RAM/ROM with loadable parameters. Log/antilog with adjustable gamma factor and gain is the other option.