received some good help in the past on another project (vacuum pump). I'm now moving on to my current project, to build a colourimeter or 430nm spectrometer for measuring the colour of beer.
This project will be encased in a wooden box with brass fixtures and fitting and use an analog output device - I'm thinking of a needle Voltmeter with a graduated colour scale, but that's quite a way down the track.
Currently, I am following this paper, http://www.academia.edu/6985992/Simple_Cheap_and_Portable_Colorimeter_for_Introductory_Analytical_Chemistry_Laboratories as the starting point using a 430nm diode and some white Das modeling clay to make a cuvette holder and housing for the LED and LDR. However it relies on resistance measurement with a multimeter, which is not part of my longterm plans.
So, I'm going to need a log amp to produce a voltage output. Which, I believe, is where all the fun begins. I guess I could build a log amp circuit, but temperature compensation, apparently, is critical to accuracy especially when dealing with transmissive sampling.
I've also looked at two log amps, the Texas Instruments LOG112 & the Analog Devices ADL5306. The first is insanely expensive, and the second not available via ebay.de which brings me to the question: for this particular application, what other options do I have, or should I just bite the bullet and get the LOG112 and move on?