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DMD Development Kit Setup and Issues

Module by: J. Ryan Stinnett, Jennifer Gillenwater. E-mail the authors

After running into many dead ends trying to create a projector-based compressive imaging NIR camera, we did some work with a stand-alone TI board, in a lab table setup. Before we began working on this project, a similar setup already existed, as shown in Figure 1. Our lab table setup is very similar, with the exception that we have black cardboard barriers to shield the photodiode from the light source. Our photodiode, light source, and target object are also of course different from those shown in Figure 1. Figure 2, Figure 3, and Figure 4 show what the new setup looks like.

Figure 1: Original lab-table version of a compressive sensing camera [1].
Original Lab-table Setup
Original Lab-table Setup (current_spc.jpg)
Figure 2: Light source, target object, focusing lens, and DMD
Camera Front End
Camera Front End (new_front.jpg)
Figure 3: TI 1100 Discovery Board and light source
Camera Top View
Camera Top View (new_dmd.jpg)
Figure 4: Focusing lenses and photodiode
Camera Back End
Camera Back End (new_back.jpg)

With this setup, we have direct control of the DMD mirrors; the TI 1100 Discovery Board has a high-speed interface that we can control using ALP (Application Programming Interface) software. To capture diode data, we use VILogger, then clean up the resulting stream in MATLAB. Thus, it seems probable that with such a setup, achieving a fast capture speed is within reach.

However, we continued to experience problems on the NIR lighting and sensing ends of the camera. The light bulb burnt most substances we tried to mount it on, and had to be positioned just right in order to reflect enough light off the target object. Further, the diode data showed a lot of noise when the signal was low, as can be seen in Figure 5. Over a long capture period, we also often observed a drift in the base signal, as shown in Figure 6.

Figure 5: Each set of pulses should be flat, as each is a set of the same random frame sent out repeatedly; the diode signal is clearly noisy
Noisy Diode Data
Noisy Diode Data (pwalsh32.png)
Figure 6: Over a capture period of several minutes, the base diode signal decreases significantly
Drifing Diode Baseline
Drifing Diode Baseline (pwalsh32tilt.PNG)

References

  1. (2007, October). http://www.dsp.ece.rice.edu/cs/cscamera/.

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