2019 Electronic Competition Question F - Paper Counting Display Device

Topic requirements Topic
analysis
Through analysis, the topic can be divided into two solutions for production.
1. Use the capacitance sensor FDC2214 to detect the capacitance of the capacitor composed of two electrode plates in real time, and calculate the number of papers corresponding to the capacitance value through software, and display the test results of the number of papers on the OLED LCD screen.
2. By changing the capacitance between pin 7-pin 2-pin 6 of NE555, the output frequency can be adjusted. The output frequency value corresponding to the measured paper can be collected by the single-chip microcomputer, and the test results of the number of papers can be displayed on the OLED LCD screen.
Because the second method has low cost, high efficiency and small error, I choose the second method here to implement this topic.
Here, the different parts of the screen display are as follows:
Basic part The screen displays the number of papers and whether the AB plates are short-circuited.
The screen displays the number of papers and the real-time frequency of the waveform generated by 555.
Overall design scheme block diagram Schematic
diagram Design description
The main part of this question is the NE555 side. The frequency f=1/T=1.44/(R1+2*R4)*inter-plate capacitance C. The appropriate frequency is obtained by adjusting the resistance. When the number of papers between the plates increases, the capacitance between the plates also decreases, and the frequency increases. The frequencies of different papers are collected and recorded through CW32 to generate a frequency library. After that, different numbers of papers are put in. The corresponding number of papers in the frequency library is found through the measured frequency, and the number of papers is displayed on the OLED to complete the answer.
Overall schematic diagram
PCB design description
The arrangement of the power line, ground line and printed conductor on the PCB should be appropriate, and try to be short and straight to reduce the loop area formed between the signal line and the return line. The power line should be larger.
Overall PCB
software description
Frequency corresponding to 1~10 sheets of paperif
(x_1ms_2>=1000){if(Paper.start==1)]{Paper.start = 0:if(feq>=50000&&feq<145000) Paper.num=1;else if(feg>=148000&&feg<175000) Paper.num=2;else if(feq>=178000&&feq<195000) Paper.num=3;else if(feg>=198000&&feg<215000) Paper.num=4;else if(feg>=218000&&feg<235000) Paper.num=5;elseif(feg>=238000&&feq<255000)Paper.num=6 ;else if(feg>=258000&&feq<265000)Paper.num=7.else if(feg>=268000&&feg<276000)Paper.num=8:else if(feg>=278000&&feg<290000)Paper.num=9:else if(feg>=292000&&feg<306000) Paper.num=10:ese Paper.num=0;
Physical display
precautions
Friends who want to make it should pay attention to the fact that the wires connecting the plates should not be connected with ordinary flying wires as much as possible, because there are many interferences in the air. I use anti-interference SMA wires.
In addition, this project needs to record a large amount of data through actual measurement. The position of the paper is different, and the frequency generated is also different, which tests the mentality.