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Will a laser beam work with a standard LDR?

Ipduo

Jul 28, 2010
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Jul 28, 2010
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Hi,

Just wondering if anyone knew whether a laser beam (~ 1mw) would work with a standard LDR, or whether the intense beam of light would permanently saturate the CdS cell?

Thanks
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
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25,510
It should work. Even at short range, 1mW isn't that powerful :)
 

trobbins

Jun 15, 2010
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Jun 15, 2010
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LDR will have a generic frequency response, which will peak at likely something in the middle of the visible spectrum. Do you have the spec sheet for your LDR? The LDR response may drop off rapidly away from its peak response. If the laser frequency is not close to the LDR peak then you may get poor or no response. You can compare LDR resistance range by using a strong incandecent light source, which has a broad spectrum.

Ciao, Tim
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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25,510
LDRs tend to have a fairly wide response. You can google for some robotic colour sensors people have built using them.

But, yes, it is likely that the response will not be optimal for red, especially the deep red of the cheap laser pointers.
 

trobbins

Jun 15, 2010
83
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Generic CdS response is pretty repid drop off imho. http://ronja.twibright.com/datasheets/cds-resistor-pgm.pdf

Diode lasers come in at 780 or 650 nominal. The 780nm may be a struggle for CdS type sensors, especially as the illuminated light area on the sensor may be quite a small fraction of the sensor active surface area,
http://www.repairfaq.org/sam/laserdio.htm#diodlm

Even with a datasheet it is worth checking the achieved resistance span with say a desk lamp quartz hal bulb for comparison.
 
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