A project log for Compact, $25 spectrometer

AMS's new AS7265X 3-chip set promises a compact, 18-channel, 20 nm FWMH spectrometer for less than $25

Kris WinerKris Winer 06/21/2018 at 00:270 Comments

20 June 2018

I received the pcbs with the Generation 2 design from OSH Park and finally put one together yesterday. Today I loaded the Generation 2 firmware onto the 4 MByte SPI flash and to my surprise I finally got an I2C ACK and discovered an I2C device at 0x49 just where it ought to be!
Here is the new board in action:

And below a close up look. I replaced the rgb led with a simple blue one (bottom right corner). Sure enough, before the firmware was loaded it was blinking once a second and after firmware upload to the SPI flash the led stayed on. This is different from the behavior on Generation 1 where the led indicator went off when proper firmware was present. I will assume the "constant on" behavior is normal for Generation 2, but I'll ask AMS. I also didn't bother populating the source 1 & 3 leds, partly because the 850 nm led I was using for one of them before never seemed to work, and also because the broad band source (yellow square thing) is bright enough for initial testing and I don't want to complicate things too much just yet.

I started working on my I2C sketch for the photospectrometer which will take a while to get right. This is partly because there are 18 channels that have to be managed including the 20 pieces of calibration data and various gain and integration time settings, etc. I have a pretty good start and it's just a matter of slogging through the excel spreadsheet (provided by AMS) with the new I2C commands and learning how to use them to get calibrated spectral data output to the pc. The GUI that came with the evaluation kit was nice and easy to use but I want something that can allow easier plotting and scaling as well as simplified storage and comparison of the data. In other words, I want the total control of a fully functional Arduino sketch that I can tailor to my needs. Here is the output I have obtained so far:

I am pretty sure version 12 is correct; the zip file I got from AMS was labeled FW_AS7265x_12V0.0. I am not sure what the Patch and Build versions are supposed to be, but at least the results aren't 0xFF anymore!

By the way, I was sent this link today. It is another YouTube video showing a product from LinkSquare that is essentially a spectrometer with nearly the same spectral range as the AS7265X that is able to distinguish between aluminum, silver, gold, copper, and titanium. It does this by measuring the reflectance spectrum and comparing to a library of spectra to identify the likely target. This beautiful device can be yours right now for the low, low price of just $549!

I wonder if the $25 AS7265X Spectrometer can do the same?