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29-05-2015, 21:08
(This post was last modified: 29-05-2015, 21:14 by
AllyCat.)
Hi,
Yes, in principle, that circuit diagram could be suitable, if you can fill in the missing information and reproduce and calibrate the hardware adequately. But that might be easier said than done.
Firstly, the Op-Amp is a TLC 2272 with Pin 1 on the right-hand side of the diagram. It seems rather "over-specified" for the task, but not too expensive so you may as well use it if available cheaply (otherwise a normal Op-Amp should be good enough for this simple "shunt feedback, virtual earth input" design).
However, the VTB5041 Photodiode seems very expensive, with a relatively "incomplete" Specification. It is described as having an "extended blue response" but this is not quantified and the peak-response is still in the IR region. Also it has only a +/- 45 degrees half-power beam angle (not the 67 degrees of a "Sine" response) which is presumably the reason for using a "diffuser". Personally, unless more data is available, I would use something like a BPW34 photodiode which has a similar detection area (~7 mm2) but close to a Sine response, and not attempt to construct a diffuser.
Unfortunately, I can't read the colour codes on the resistors in the photo; it looks as if R1 might be 47k or 4k7 but both of these values seem to be (much) too high for the photocurrent delivered by a 7 mm2 photodiode in direct sunlight. So maybe the "diffuser" is also a strong (i.e. low transmission) optical filter? Do you have any more details of the resistor values or the physical appearance of the diffuser? The other component values don't seem too critical, but do use a high stability "cermet" pot.
Cheers, Alan.