Month: April 2021

Breyden Wood’s Status Report for 4-3-21

This week, I have made significant progress with the camera and was able to resolve the significant issues with the color we have been seeing for the past week and a half. This task was made significantly easier with the aid of the oscilloscope we were able to borrow from the ECE labs, and the three major bugs we had would have been extremely difficult to detect without the scope. The first bug found was with the voltage of the logic the camera outputs. After scoping the data lines, it was found that the camera outputs voltages around ~2.6V for signals that are “high” with a significant ripple in the voltage of around +/- 0.1V. Our FPGA was doing GPIO logic at 2.5V, which meant that, with these ripples, the voltage for a logical “1” was occasionally dropping below 2.5V. This would cause the FPGA to occasionally read a negedge or a “0”, which was creating both visible static in the data of the image and occasionally distorting the entire image altogether when the clocking signal from the camera had false negedges. This was resolved by lowering the FPGA’s IO logic voltage. The next issue was with the timing of reading the data. Lots of documentation online suggested we read data values in at the negedge of the pixel clock, however, the rise time of the clock and data signals were such that reading at the negedge of the clock would result in incorrect data, leading to further distortion in the image. This was easily resolved by changing the logic to read at the posedge, which further reduced static in the image.

Lastly, the biggest bug we had was an extremely subtle bug in our I2C timing for programming the camera’s settings from our Arduino. We noticed that the bit pattern the camera was outputting didn’t seem to match the camera settings we applied from the Arduino. Furthermore, while some of the camera settings seemed to change things in the image, some of them didn’t. After much investigation, the oscilloscope revealed that the Arduino code we had been using to program the camera the entire time had been operating at a frequency of ~475KHz, slightly above the 400KHz maximum specified by the OV7670’s manual. We redid the Arduino code to communicate at a lower frequency and that change allowed us to correctly set the bit pattern, white balance, and other camera settings with the expected resultant effects.

In summary, we now have color input and output from the camera to the FPGA to the VGA display, which is a significant part of our MVP. I am now back on track for the interim demo and expect to spend most of this upcoming week working with Jullia to finalize the image combiner and redoing the memory interface to match our final specifications.

 

This image shows the timing and variance in the voltages. The clock line is in yellow and one of the data lines is in green.

This image shows the working color output of the camera. The colors are slightly off (mainly in deep blues and greens) due to the white balance not being fine-tuned. This has since been rectified in the lighting of my room, however.

Team Status Report for 4-3-21

This week, our team made significant progress towards our MVP and beyond and we are nearing the level of work we planned to have done for our interim demo.

Firstly, we were able to resolve the camera color issue that has been plaguing our camera-to-FPGA-to-monitor path. This represented a significant risk to our project as correct color output is critical to both the quality of the projected image as well as our chroma-keying algorithms. With the help of an oscilloscope we acquired this week, we were able to find and resolve the issues and now have correct color output working (see Breyden Wood’s status report here for more details).

Secondly, we were also able to construct a full-scale prototype of our pyramid that will be placed on the TV for our illusion to work. When scaling up from 1:2 we ran into an issue with the materials distorting too much, but we were able to resolve this by fixing a cardboard lid to the top of the pyramid. This not only provides much better structural rigidity but also improves contrast and clarity as well.

Finally, we have begun implementing the image filters we plan to use on the FPGA in Python. While it is not written in Verilog (and thus is not synthesizable), this allows us to quickly verify and tweak our algorithms prior to writing them onto the FPGA. More details on both this and the pyramid construction can be found in Grace An’s status report here.

We have identified a significant risk of chromatic noise in the output of the OV7670 cameras, which threatens the video frame quality we can achieve from our final project. To mitigate chromatic noise, we will ensure that our live studio is lit up as brightly as possible, as the OV7670 cameras’ chromatic noise vary with lighting. We will also change our design to include a simple noise reduction image filter in hardware, which may replace (or add onto) our sharpness filter in the image signal processing module. We also changed the design of our holographic pyramid by adding a cardboard top in order to straighten the pyramid sides and dim the area within the pyramid to improve quality of reflected images. This change in design does not add to the cost of our project as cardboard is readily available.

Some tasks in the schedule have shuffled due to the previously mentioned  issues, although not in any way that threatens our MVP. Debugging the color scheme issue took up much of the past two weeks. Image filters were worked on this week instead of the live studio construction, which will occur the following week. Our updated schedule is shown below: