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70 PCB007 MAGAZINE I NOVEMBER 2020 ter, the ultraviolet-visible light spectrophotom- eter, and the infrared spectrophotometer are the most common. Only the first two are used in printed circuits. The colorimeter is used to analyze for copper in electroless copper, acid sulfate plating, and hydrogen peroxide-sulfu- ric acid etching, and nickel, cobalt, palladi- um, and chromium in their respective plating baths. The ultraviolet-visible spectrophotometer is now being employed because of their micro- processor control units. By selectively scanning wavelengths and using the first and second de- rivatives of the absorbance curves, these spec- tra can be compared to stored spectra and con- centrations calculated automatically. Many of the units can control replenishment and sam- pling directly. Analysis that can be performed in this way is determining the Au(I) and Au(III) in gold plating baths; the proprietary additives, nickel, and impurities in a watts nickel bath for fin- ger plating, and various copper analyses. The human can be removed, and the wavelength expanded with common UV-VIS spectropho- tometers. Here are six common UV-VIS spec- trophotometers, sensitive from 340–1,000 nm (Figure 7). Recently, with the advent of cameras in your common cellphone, many do-it-yourself (DIY) spectrophotometers have been designed. All work on the principle that LEDs have specific wavelengths of light and eliminate the need for expensive optical wavelength filters or mono- chromators gratings. A graph of the wave- length of 12 different LEDs available is shown in Figure 8, along popular DIY spectrometer [1] used by middle schools and high schools. One specific DIY spectrophotometer called the Lego spectrophotometer is made from chil- dren's Legos and a wavelength grating cut from any used CD. The Raspberry Pi or Ardu- ino camera module provides wavelength sen- sitivity from 400 nm to 900 nm. Design and Figure 7: Six photos of common UV-VIS spectrophotometers available from laboratory supply companies and their wavelengths. Some of these have been available for the last 60 years, like the Spectronic 20.