Hello everyone! We are the C-level team from Shanghai Jiaotong University (Mao Zhenjie, Wang Wentao, Yang Haoning) . This year we participated in the TI Cup Shanghai College Student Electronic Design Competition and were fortunate to win the first prize. It is a pleasure to be invited by Texas Instruments and Dahlwen to share our participation experience.
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The epidemic is affected, training is restricted
Due to the impact of the Shanghai epidemic, the Shanghai video game is postponed to October. Even so, our pre-match preparations are still very hasty. In the spring semester of 2022, we took classes online almost the entire time, and the courses originally related to circuit design and production were not carried out normally, which made us lose the opportunity to enter the laboratory for practical operations. After the start of the fall semester, the reappearance of the epidemic on campus casts a shadow on our preparation process, and the National Day training camp was not held as scheduled. Fortunately, all parties overcome all difficulties in the end, so that this city competition was successfully held. At the same time, in order to take care of other students who still have the epidemic on campus during the quarantine period, the organizer extended the schedule by one and a half days, giving us more time to produce the works. In this way, the four-day and three-night market competition turned into six-day and five-night market competition, adding a more unforgettable experience to our electric competition career.
Our group photo
The beginning of the competition: a confusing plan design
On the first day of the competition we went to the laboratory early to wait for the issue of the competition. After browsing all the questions, we had a fierce discussion on topics. Since we have studied the courses of "Analog Electronic Technology" and "Engineering Practice and Technological Innovation", we are familiar with hardware circuit design, electrical characteristics of components and microcontroller programming, and finally decided to choose the C question - Active Filter Amplification .
After successfully determining the topic, the next step is to demonstrate the plan. The selection process of the solution is not as smooth as the topic selection. We were confused at the beginning. How to realize the core of the preprocessing circuit - the automatic gain control circuit?
automatic gain control circuit has two main implementation forms: using variable gain amplifier (VGA) or variable electric modulation attenuator (VVA) to achieve dynamic range. The two solutions have their own advantages and disadvantages. The former usually has a smaller bandwidth and a lower frequency, while the latter can achieve a wide range of applications, and the number of VVA and low-noise amplifier products in each frequency band is wide. However, considering the characteristics of the input signals in the question and combining existing experimental equipment and theoretical knowledge, we ultimately did not choose the packaged automatic gain control module, but chose to use a microcontroller to process digital signals to achieve accurate control and real-time control of the gain. For microcontrollers, we chose TI's TM4C1294NCPDT, which has convenient operation methods and efficient performance that enable us to complete functions faster. After selection, we chose TI's DAC8043 among the massive digital-to-analog conversion chips because it is programmable! In addition, since the input signal amplitude is small, in order to calculate the amplification ratio more accurately and protect the microcontroller overcurrently, we decided to add a conditioning circuit to proportional amplify the input signal and bias the DC to , and then input it to the ADC interface of the microcontroller. On the same day, we purchased the chips and modules we needed.
Laboratory environment
The theoretical system of low-pass filtering and high-pass filtering circuits in the second half of is relatively complete, and there is already quite mature experience to learn from. Through the calculation of the index in the question, we found that using a fourth-order filter can perfectly meet the requirements! But we did not use the fourth order, but instead used the fifth order filter design.This is due to the inevitable error between the theoretical circuit and the actual circuit. From the difference between the label value and the actual value of the components, to the circuit wires and operational amplifiers are not ideal components, various influencing factors make it very likely that the performance of our actual circuit will not be able to achieve the simulation effect. Therefore, when designing the circuit, you must leave sufficient "surplus" to ensure that even if the actual circuit is not ideal, you can meet the index requirements .
overall design block diagram of circuit
Previous competition: twists and turns circuit welding
After designing the basic circuit diagram, it is the specific implementation of the circuit. We first checked several test points in the soldered signal conditioning circuit , but the result did not meet expectations and the circuit failed! In order to find out the problematic circuit part, the three of us divided into two groups. One of us simulated and verified various types of faults that may cause this result. The other two analyzed the possible problems in the circuit together, and used a multimeter to conduct virtual welding and missing welding inspections on the solder joints one by one. Finally, it was found that it was caused by virtual welding of a wire.
After a day of welding and microcontroller programming, our first part of the preprocessing circuit function is basically implemented. After many debugging during this period, no matter how they were modified, there was always a problem with the output test points of the microcontroller part. We once suspected that the microcontroller chip was damaged. Later, I accidentally discovered that it was because the DAC of the patch component was too small, causing an incorrect short connection of some pins, which delayed us a lot of time to check the errors. Various strange errors will occur later, such as output detection point welding errors, power supply wire welding errors, component access errors, etc. So be careful during the welding process, and would rather be slower than be impatient, and be too rush .
The replaced board was not soldered
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Next is the test of the filter circuit. We are still not that lucky, and there are problems with the output of both circuit modules. So it was another familiar error checking process. In order to accurately find out the problem, we copied the filter circuit in the simulation software to observe what effect the circuit should achieve in theory, and then add short circuit, circuit breaker, component value errors and other problems to analyze what is wrong with the circuit we made.
Low-pass (top) and high-pass (bottom) filter circuit simulation circuit diagram
Mid-term competition: Unstable automatic gain
After completing hardware welding, it is connected to the microcontroller for joint adjustment to realize the automatic gain function. The preprocessing circuit that had been performing well before during this process became very unstable after one night, and we were immediately nervous. First, I checked the hardware circuit again. After several attempts, I guessed that there was some bug in microcontroller programming. After all, the hardware circuit was still good yesterday and would not break after being left overnight!
After the students in charge of the software modified and repeated trials overnight, they finally found that the input signal exceeded the signal range that can be processed in the program, resulting in some errors in the output results of the program. After fixing some logic vulnerabilities, the automatic gain circuit successfully achieved stable output.
Later in the competition: Repeated value debugging
Another day passed, and we still failed to find the problem with the high-pass filter circuit.At this time we made a decision: re-solder! Time waits for no one. During this welding process, we learned from previous experience, made steady progress, and no longer cared about the "appearance" of the circuit. After an hour and a half of anxious waiting, the new soldering board was born, and we successfully realized Qualcomm this time! However, due to the cutoff frequency requirements, we began to adjust the rounding of the capacitor again. first performs simulation verification on the computer, determines the modification plan, pull the cutoff frequency into the range by connecting a small capacitor in parallel, and finally connects the power amplification module .
Finished product of filtering and amplifier circuit
Competition end: Reports written in turn
Within a few hours in the last morning, our main job is to conduct the final inspection of the circuit, welding and circuit board fixation of some detection points, and to improve the writing of experimental reports. We first completed the general content by a person, then measured and recorded each output point, and analyzed and wrote the first experimental report. We then read and modify the report one by one. After two verifications, the final experimental report is basically formed. Then print the report and seal it with the final work.
The work before the box is sealed
At this point, our Shanghai video competition process ended perfectly. Next is waiting for the final evaluation. At the moment when the work is sealed, we feel relieved.
After experiencing the school test and the city test, we finally won the first prize. After learning the news, we were all surprised, but also very happy. After all, our efforts over the past few days have received a generous reward. Although we rushed to the stage after the temporary team training, we still successfully completed the work with unremitting efforts and unity. Through this competition, our circuit design and production capabilities have been improved, and the team's cooperation has become more tacit. In the process of completing the work, we fully utilized the knowledge we learned and expanded new knowledge. Overall, this is an experience that has benefited us a lot.
At the end of the finale, we can also give all the new players preparing to participate in the electric competition some of their own experiences and suggestions:
When preparing for the competition in , pay attention to to master some relatively basic circuits , such as the basic amplification circuit, filtering circuit, etc. Some more complex circuits may be difficult to encounter, but you don’t have to panic when encountering them. Generally speaking, you can find solutions by looking up various materials. If you encounter it normally, you can write it down as a way to accumulate knowledge, such as this automatic gain control circuit.
time to . After getting the question, you still need to leave enough time for to have a clearer and in-depth understanding of the entire circuit and the functions to be implemented by each module. Then find as many solutions as possible, and make the best choice after fully considering the advantages and disadvantages.
circuit design , should fully consider the actual engineering , leaving sufficient fault tolerance space for the actual circuit. In terms of circuit welding, for more complex large circuits, multiple inspection points can be divided into sections to check them one by one. During the welding process, learn to make good use of multimeters for virtual welding inspection, and can be re-welded directly if necessary. I hope that all the students who participate in the electronic competition will also achieve good results!
Article link:
https://mp.weixin.qq.com/s/z4pSTFYwMPGvrlJEQ4-7zQ
Reprinted from: Daerwen Says, Author Shanghai Jiaotong University C-team team
Article link: Direct hit to the electric match | Repeatedly push back and start over! What exactly do you do in 6 days and 5 nights? (Full Guide)
