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Table of contents for frequently asked questions on Texas Instruments' spectroscopy evaluation modules.
2. What is the specification of the cuvettes that ship with the DLP NIRScan?
3. I just got my DLP NIRScan Nano. What should I scan?
The DLP NIRScan™ Nano is designed for contact scanning so objects which are flat and uniform make good test subjects. We advise putting the sample in a plastic bag if there is any risk of the sample contaminating the electronics on the spectrometer.
Some have asked if Texas Instruments keeps a database of scans. We do not. However, we do provide some example scans with the TI Design for the DLP NIRScan™ Nano: http://www.ti.com/tool/tida-00554
For a detailed discussion of these issues and some others around getting started with your DLP NIRscan™ Nano, read this thread: https://e2e.ti.com/support/dlp__mems_micro-electro-mechanical_systems/f/983/t/456792#pi319142=1
4. I need information on Sampling Techniques.
To capture the absorption spectrum of a sample, spectrometers commonly used one of these sampling methods:
Before taking a scan, samples need to be prepared for consistent presentation. A consistent presentation minimizes sample-to-sample differences and provides a more uniform sample.
Some of the preparations require that:
Some applications require the avoidance of contact between the sampling head and the system to prevent contamination of the sample or cross-contamination between samples.
There are some major differences between contact and non-contact sampling.
A sample’s absorption of light is measured as the ratio of the light absorbed by the sample and the light incident to the sample. To determine the amount of incident light to the sample, a baseline must be capture. This baseline is referred to as the reference measurement. The NIRscan Nano contains a stored reference measurement in its EEPROM that was created at the factory.
The creation of a reference measurement depends on the sampling method:
This reference measurement must be performed periodically to account for drift due to:
5. I have questions about the scanning process.
It is possible that when you are scanning you'll get a result like the image shown below. These large dips are caused by the patterns that are used for measuring adjacent wavelengths alternating between two different widths or number of DMD columns used to take the measurement.
For example, low values might be captured when the pattern is 7 DMD pixels wide, while the higher values might be captured when the pattern is 8 DMD pixels wide. The intensity measured at the detector is proportional to the number of DMD mirrors that are set in the position to reflect incident illumination toward the detector, so as the number of pixels changes in a back and forth manner, the measured intensity will also vary.
More explanation of this effect is available in section 4.2 and figure 9 of the DLP® Spectrometer Design Considerations application note. Specifically, it states:
It is common that the number of columns between the minimum and maximum wavelength to scan is not evenly divisible by the number of wavelength groups desired. In this case, there are a few ways to proceed:
The DLP NIRscan™ evaluation module uses the second method above. The DLP NIRscan™ Nano uses the first method above. Therefore, the intensity graph of scans performed with the DLP NIRscan™ Nano will not have this behavior.
b.Why do the reported wavelengths differ between two scans defined by the same parameters?
6. I want to know more about the inside of the NIRscan Nano
If you wondered how the DLP NIRscan Nano Evaluation Module (EVM) works, we have disassembled it to show you its internal components and optical paths.
Please note that any disassembly of the optical engine voids the warranty on the NIRscan Nano EVM system and removing the cover on the optical engine allows dust and smudges to collect on the optics affecting its performance. Also, removing the cover might move the optics, slit, and detector out of alignment requiring factory realignment and recalibration. Removing the slit, Indium Gallium Arsenide (InGaAs) detector and DLP2010NIR will require the system to be realigned and recalibrated at the factory.
In short, do not try this at home.
Let’s begin with a quick overview. DLP spectrometers replace the traditional linear array detector with a digital micromirror device (DMD) for wavelength selection and a single point detector. By sequentially turning on a set of columns pertaining to a particular wavelength of light, the light is directed to the detector and captured. By scanning through a set of columns across the DMD, an absorption spectrum can be computed.
DLP technology in Near-Infrared (NIR) spectroscopy provides the following advantages:
Currently, DLP NIRscan Nano EVM software supports variable resolution and Hadamard patterns. Variable intensity and custom spectral filters are not supported.
In this picture, you can see the major components of the DLP NIRscan Nano EVM:
Removing the cover to the optical engine reveals the DMD and Detector board:
Now if we removed the Reflectance module, you can see the slit:
Now that we’ve gotten inside, let’s take a look at how the light is manipulated.
The light reflected from the sample is gathered by the Collection lens and focused into the optical engine through the input slit. The slit size is chosen to balance wavelength resolution with signal-to-noise ratio (SNR) of the spectrometer. This spectrometer uses a 25 μm wide by 1.69 mm tall slit. The light that passes through the slit is collimated by the first set of lenses, passes through an 885-nm long wavepass filter, and then strikes a reflective grating. This grating, in combination with the focusing lens, disperses the light into its constituent wavelengths (multi-colored light rays). The focusing lenses form an image of the slit at the DLP2010NIR DMD. Different wavelengths of this slit image are spread horizontally across the DLP2010NIR DMD. The optical system images 900 nm wavelengths to one end of the DMD and 1700 nm to the other end, with all other wavelengths sequentially dispersed in between.
For more information on DLP NIRscan Nano EVM, refer to the DLP NIRscan Nano User’s Guide.
7. Where can I find more documentation on developing a DLP technology-based spectrometer?
The following TI documentation provides further information on developing a DLP technology-based spectrometer:
The following reference designs are available:
The following User's Guides are available:
The following videos are available:
The following DLP technical documents are available:
8. Can I change the resolution and wavelength range of DLP NIRscan and DLP NIRscan Nano?
The optical architecture of the DLP NIRscan and DLP NIRscan Nano can accommodate various resolution and wavelength ranges with minor changes to the optical layout.
9. Compiling and modifying Tiva software
* Compiler switch to remap Scan button
* 0 = Scan button input from Expansion Connector J3 pin 8
* 1 = Scan button input from Scan button on Tiva Board
#define SCAN_BUTTON_TIVA_BOARD // PQ3
#undef SCAN_BUTTON_TIVA_BOARD // PK3
/*** Compiler switch to enable BLE advertsing at startup*/
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