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his chapter is dedicated to discussing the final results which I viewed in the previous chapter, mentioning some of the challenges that I have faced while working on this project and lastly, concluding this report.Let us start by discussing the final results. The fact the same code worked perfectly when tested on the first prototype -which mimics the final one- but failed when tested with the final prototype, left me with a list of suspicious reasons for this failure. First possibility is that there is a problem with the RF module embedded on the client’s board. To eliminate this possibility, I simply redone the same test but this time I connected the client directly to the PC using a UART to USB connection. The results were similar to the previous ones, therefore, no problem with the wireless connection.
The code cannot be the reason for the failure because the same code worked fine with the first prototype.
Adding the TVS Zener diodes might be the problem -I thought that drop voltage or even the impedance of the diodes might affect the input signal-. To eliminate this possibility, I de-soldered them as shown in Figure 21, then tested the prototype but it gave me similar results.
Currently, I am suspecting the soldering of the ADS1293 or maybe it was destroyed due to an electrostatic discharge. I did not have enough time to validate these theories, but I will do that soon.
An important thing to add here is the adaptability of the MATLAB algorithms. I tried my best to make them as adaptive as possible. Eventually and using some tricks, the
algorithms became adaptive to some factors such as the change in sampling frequency which can happen when changing the hardware system that is used for acquiring the measurand.
But they are not immune to sudden changes in the amplitude of the input signal and this fact makes the system unsuitable for real-life applications at its current state, as those sudden changes in the shape of the signal have to be taken into account.
Moreover, the filters were designed and tuned to deal with noises and artifacts similar
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to those encountered in the signal which was used for testing the algorithms, meaning that I cannot claim that my algorithms -in their current state- can be used as an
inclusive solution.
The traces in the PCB layout are somehow long. This issue was solved in my modified design.
Back to the final results; during the last 10 days, I was trying to work the final
prototype out. Having little room of time -two days before the demo day- left me in a reckless and hasty state. This resulted in me losing my critical way of thinking and engineering approach for troubleshooting. Overall, this was not the perfect condition for dealing with such failure.
After the demo day, I started to change my mind regarding the situation of the project;
instead of solving the problem with the hardware -which shall waste a lot of time-, I will focus on the MATLAB algorithms. And to do so, I will activate plan B (modified version of the hardware that was developed before in my BSc thesis (39)) which I call
“PULSE2.0b”. As a matter of fact, I have already done that by testing the hardware of
“PULSE2.0b” and it worked perfectly -see Figure 47-. Unfortunately, the results have not been well documented yet and thus, I could not showcase them in this report.
Figure 47: Output signal using PULSE2.0b HW
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Now, I will leave you -dear reader- with some of the challenges that I encountered during this project;
1) Hardware orders: In this kind of projects, the prototyping phase is expected to start earlier in along the schedule. This was case in my
project, and to waste no time, I needed to start as early as possible. To do so, I had to order all the electronics needed for prototyping. It was
possible to place the order through the IT department, but this meant that I will wait for a very long time until I receive the components. This is due the tedious formalities needed to be considered when placing such order through the department. The only solution was to find a sponsor for my project. Following the “3F” rule -family, friends and fools-, my father approved on sponsoring me.
2) PCB footprints and libraries: One of the most annoying issues was to find the right footprint for each component. Of course, the designer can design the footprint from scratch, but this will be a tedious process and can be exposed for human errors. To solve this problem, I had to fetch for each library of every component, some of which were supported by Altium, so I was able to find them in their website. Other manufacturers were not supported by Altium, but I found their libraries (Schematic, PCB or Integrated libraries) which were designed using different software such like Eagle. Thanks again to Altium Designer (AD), one can use their Import Wizard tool to convert libraries from different software and import it to the project in AD.
3) In-circuit programming/debugging: Since the ESP8266 will be soldered to the PCB, and since this board is still used as a prototype, that means that I will need to reprogram it or debug it. There are two ways to do that; one is to de-solder the module, program it and then re-solder it again. The other solution is to do an in-circuit programming. This can be done by connecting the module to another programmer using UART bus. To do that, I made use of headers and shunt connectors to change the working moods of the system.
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4) Ground plan under the antenna: This was the most expensive mistake for me. I sent the fabrication files to the manufacturer company and later received the PCBs. When I showed them to the supervisor, he
immediately noticed a fatal mistake in my design. I naively poured a ground plan beneath the antenna of the ESP8266 module resulting in blocking any transmission to occur. Later, I modified the design by cutting the area under the antenna as shown in Figure 16.
5) Soldering SMD components: Before soldering the SMD components using the hot air gun, one must apply the solder paste over every single pad.
These pads are very tiny that it was impossible to apply the solder paste even with a micro needle. The solution was to use the so called “stencil”.
Stencils are basically a solder mask and can be printed using a knife-cutting machine -see Figure 48- and so I did. Thanks to my friend Abdul (36) -a PhD student in the Microsystems department- the stencil was fabricated and used for applying the solder paste successfully.
Figure 48: Knife-cutting machine
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In the end and as a conclusion to this work, if I were asked what is one thing that I have learnt during this project course, I would answer by quoting “Hardware work does not finish, it can only be ended” by Alexander Medvedev.
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