----- Original Message ----- From: "John Popelish" Newsgroups: sci.materials,sci.optics,sci.electronics.design Sent: Sunday, May 02, 2004 7:49 PM Subject: Re: IR Cutoff filter
: Leeper wrote: : >
: > I'm trying to reduce the IR response, so that the sunlight IR doesn't mask : > the : > visible light I am trying to measure. : >
: > Modulation and all that will not work, I need to know the amplitude of each : > Red, Green, and Blue device. : (snip) : : Have you looked at any photo diodes that have narrow band visible : filters built in like: :
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: Or only sampling the AC of the switched light source and letting the DC component the sun light fall out you only get the LED reading with none of the back ground noise from the sun. Do a 180 degree phase shift at the sensor and amplify to signals exactly the same and combine them at the end and any thing you have left is the common mode error. Go back and find the schematic for an old Instorn amplifier using vacuum tubes to see how this is done. Gordon
Gordon Couger Stillwater, OK
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