Author: tbejos

This week I worked on reading the OpenCV documentation to get a better understanding of how to capture webcam input in python. I was able to find a Python script that allows us to get the webcam input and display it on screen and am trying to figure out the best way to overlay an image onto it. This will allow us to overlay a heatmap onto the camera input so that we can show where the signals are coming from. I also helped to debug the hardware that we were using. For some reason one of the outputs from the downconverter was quite a bit lower powered than the other and we figured out that when we swapped to the other downconverter we did not have this issue, it leads us to believe that something may be faulty with that board and it took a while to figure that out. Once we switched this board we did additional testing on the correlation/synchronization of the SDRs so to help with this I wrote an additional binary for the STM32 to tell the VCO to output a 150 MHz signal so that we could skip the downconverter in order to work with just the SDR’s.

This next week I will help the team integrate the remaining two SDRs and continue working on overlaying images to the camera feed in Python so that we can start getting to the final stages of our project.

This week we made some large breakthroughs. Initially we were planning on using an Arduino since we had many available to us and they are relatively easy to program. The only challenge with this is they use 5V logic and the Voltage Controlled Oscillator we are using uses 3V3 logic levels meaning we need to convert them. We attempted to use the Sparkfun Logic Level Converters however the method of switching they use were not fast enough to support the slowest SPI speed of the Arduino. My team members considered using a Raspberry Pi since it uses 3V3 logic levels so I wrote a quick Python script to configure the VCO in case they did end up using the Rasberry Pi. Due to accessibility issues my team members ended up not using the Raspberry Pi but had a Ti MSP430 available to them which uses 3V3 logic levels so we attempted to use that. It looked promising since there was an IDE called Energia which used Arduino libraries to program it so the code I wrote this week should work. Unfortunately we had some issues setting up the development environment for that chip and none of us had experience with the platform so we moved on. My team members were able to borrow an STM32 Nucleo board, a platform with which I am very familiar with, so I rewrote the program to set the VCO registers for this microcontroller and we were able to get it to working and use it with our downmixer.

I spent a lot of time this week writing the code to program the VCO (for multiple microcontrollers) and next week I will start on the heatmap and webcam capture code.

This week I finalized the last few products that we needed to order. After some careful consideration I found the downmixing evaluation board that we plan on using, it features dual channel interfaces meaning we can connect two antennas to it, and it also is 50 Ohm impedance matched meaning we don’t need any additional hardware to prevent reflections on the signal line. We also found some WiFi antennas that seemed relatively directional without sacrificing field of view too much so that we can get sufficient overlap to get meaningful information from each antenna. The last product we ordered were the SMA cables needed to to connect all of these devices. By using these cables we are able to space out the antennas accordingly so that we can perform beamforming.

We also spent some time this week on administrative tasks as we needed to organize our task breakdown in order to make sure we are able to complete everything on time. By making a more detailed breakdown of tasks we will be able to stay more focused and not spend as much time trying to decide what to work on next. This upcoming week we hope to start receiving components so that we can start testing with the actual parts that we will be using. This will allow us to start working on solving any problems that may arise when we start combining these modules.

This week we had design presentation’s which took up some of the time we had planned for this week. Outside of the design presentations I mostly spent this week finalizing the components we plan to use for our RF Front-End circuit. During this time we had a meeting with a CMU Graduate student who is doing research in this area so that we could discuss some of our plans with him to help ensure some of our assumptions were correct. This graduate student was also a valuable resource for helping learn about some other techniques for sampling such as I/Q Demodulation which may be useful in getting information from the radio signals.

Now that we have most of the components selected I plan on drafting the schematic and then scheduling a meeting with Professor Carley, since he does research on RF Circuitry, in order to review the schematic and again helps us identify some possible flaws we may have made so that we can finally go ahead and order our PCB’s. Regarding the schedule I believe that I am slightly behind on the PCB design but do not foresee it taking up too much of our slack so I still believe that our project is on pace.

This I was doing research into what components we need in order to get meaningful data from the antenna’s. In our weekly meeting it was brought to our attention that there was likely additional circuitry needed in between the antenna’s and our ADC. Since specific information was not immediately available to us about this I did some research in order to try and figure this out.

During this research one thing I found out is that we will likely need to use an amplifier to boost the signal. I was not aware that RF signals were as low power as they are so in order to avoid noise and get a higher Signal to Noise Ratio (SNR) we will need to use an amplifier, this will also amplify noise, however it should be to a lesser effect. I also found that some circuits make use of a bandpass filter in order to help get rid of some of this noise and smooth the signal, this is something I will keep in mind as we start to design our circuit.

I was unable to find too much more detail however I will keep looking and earlier in the week we reached out to a graduate student at CMU doing similar research and hopefully they will be able to give some additional insight into some of the challenges.

This next week I will continue to search for circuitry related to antenna’s and will continue doing research so that we can get started on the design of our PCB as soon as possible, since we will not only have to create the PCB but also wait for it to be fabricated and shipped, and then also wait for the components that will be going on it to be shipped as well. In order to minimize the impact of this delay I will try and make sure we can order both parts and the PCB as soon as possible.

This past week I spent some time preparing for my team’s project proposal presentation which helped me get more comfortable with talking about our project and helped me be able to explain it to others better. It also helped me to reinforce some of the parts of the project that I was previously less informed about.

Regarding moving forward with the project I started to come up with a plan for how we were going to setup the antenna array. I came up with an idea for a 3D printed or machined piece of plastic that would allow us to place specifically spaced holes for the antennas to go through. By attaching the antenna’s to a rigid body we would be able to get them at very specific spacings and angles in order to get the best results for beamforming. It would also allow us to quickly prototype if we needed to make adjustments to the spacings in the future (note: while outside the scope of our capstone project this theoretically means that our overlying system could be adapted to support beamforming with different antenna’s and spacings for other frequencies). Since the antennas would be mounted to this board we would connect them to a custom PCB over individual wires, and then use a larger header on that PCB in order to interface it with either our FPGA or Software Defined Radio system.

While I still need to discuss it with my group after additional research I personally believe that GNU Radio will be more difficult than trying to implement our own DSP functionalities in an FPGA. This upcoming week we will start focusing more on the exact spacing for our antenna and start searching for which specific antenna’s we are going to order so that we can get started with prototyping as soon as possible. I will also get started on doing research into the kind of requirements needed for making a PCB with high frequency RF signals. Some key focuses for that will be trace impedance, trace width, trace isolation (to prevent cross-talk/noise), and I will try and find any other possible best practices.