> The Instruction manual PDF on then page you linked to has a very
> simplified explanation.  AFAICT: ambient light, or a target outside the
> operating range would cause both photodiodes to receive a similar amount
> of light, but a target within the focal range will cause one detector to
> receive more light than the other. By setting a threshold against the
> ratio of the two photodiode currents rather than the absolute value,
> variation in the total amount of light falling on the detectors will be
> ignored (within the dynamic range of the sensors!), but it becomes
> sensitive to the distance to the target.
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>=20
> Cheers
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> Mike

Thanks Mike. Yes, from the links in Xiaofans reply that's pretty much how t=
hey=20
describe the operation... Let's say the two photodiodes are called R1 which=
 is=20
illuminated by near objects, and R2 which is illuminated by far objects (be=
yond the=20
focal plane and considered "background"), then the condition for deciding t=
hat an=20
object is within range is R1 > R2.
--=20
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brown@clear.net.nz



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