Re: Linear light-sensing circuit required

On Sun, 22 May 2005 00:05:56 GMT, "Kryten"
<kryten_droid_obfusticator@xxxxxxxxxxxx> wrote:

>Hi all.
>
>I'm trying to make a circuit to sense the whiteness of a surface.
>Like white = 5V, black = 0V, and linear between.
>
>I bought an SFH2030 photodiode which gave about 20 mV difference measuring
>the reflected light from a cheap red LED.
>
>Googling the web for a good circuit, I found this one
>
>http://www.megspace.com/science/stp/pmt/sfh2030f.html
>
>which is a bit overkill, I don't need to measure starlight.
>
>Corresponding with the author, he said he still wasn't getting the circuit
>working satisfactorily.
>
>Anyone got any good tips about working with photodiodes?
>Like whether they are best run in current or voltage mode, good transistor
>circuits, do they need particular op-amps (most circuits I see seem to
>insist on high-impedance CMOS op-amps not popular ones like LM741/LF351 etc.
>
>Cheers, K.
>
Use in current mode to be linear. Just need a transimpedance amp.
Basically, one op amp and one feedback resistor.


Steve J. Noll | Ventura California
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