2019 Question F: Reappearance of paper counting display device

2019 Question F: Reproduction of Paper Counting Display Device 2019 National First Prize

Team name: Yi Jiajing

Team members: Li Gaojing, Li Feiyang, Zhang Jiaming

Instructor: Experiment Center

Competition topic: Paper counting display device

1. Task

Design and make a paper counting display device, its composition is shown in Figure 1. Two parallel plates (plate A and plate B) are connected to the measurement display circuit through wires a and b respectively. The device can measure and display the number of papers placed between plate A and plate B.

2. Requirements

1. basic requirements

(1) The metal electrode parts on plate A and plate B are both squares with a side length of 50mm±1 mm, and the lengths of wire a and wire b are both 500mm±5mm. The measurement display circuit should have a "self-calibration" function, that is, before the formal test, different numbers of papers placed between the two plates are measured to obtain measurement calibration information.

(2) The measurement display circuit can self-test and report whether there is a short circuit between the electrodes of plate A and plate B.

(3) Measure the number of given papers placed between the two pole plates ranging from 1 to 10 sheets. Each time the paper to be tested is placed between the plates and fixed, the measurement is started with one click, the number of papers to be tested is displayed and a beep sounds. The time from pressing the same measurement start button to the beeping for each measurement shall not exceed 5 seconds. During this period, there shall not be any manual intervention on the measuring device.

2. play part

(1) Keeping the electrode plates and wires unchanged, measure the number of given papers placed between the two electrode plates ranging from 15 to 30 sheets. The relevant requirements for the measurement start button, display beep, measurement time, and no manual intervention are the same as "Basic Requirements (3)".

(2) With the electrode plates and wires unchanged, measure the number of given papers placed between the two electrode plates at least 30 sheets. The relevant requirements for the measurement start button, display beep, measurement time, and no manual intervention are the same as "Basic Requirements (3)".

(3) Others.

3. Description

(1) The paper to be tested is always 70g A4 copy paper, and the specific positions where the electrodes of plate A and B contact the paper to be tested are not limited. When testing, use paper of the same specification provided at the testing site.

(2) Plate A and B can be made of metal plates or double-sided copper-clad laminates (referred to as double-sided plates). One side of the double-sided panel is processed into a square copper-clad electrode plate with a side length of 50mm±1mm. The other side is allowed to have via pads and leads for welding wires a and b, but no copper-clad surface mesh is allowed. It is prohibited to use multi-layer boards to make plates.

(3) Plate A, B and wires a, b (signal lines) must be a two-wire parallel plate structure, and the electrode of each plate can only be connected to one signal wire; the cable type and arrangement of wires a, b There is no restriction on the way of cloth. Plate and wires that do not meet the above requirements will not be tested.

(4) Contestants can design the structure between the electrode plate and the paper by themselves so that the two electrode plates can press or clamp the paper being tested. The structure must not increase the area of ​​the electrode plate; the electrode plates A and B and the wires a and b must not be installed. Or connect components, other sensors or measuring instruments, otherwise it will not be tested.

(5) "Self-calibration" should be completed during the restoration preparation stage before testing, and no "self-calibration" operation is allowed after the test starts.

(6) You can only press the same start button (can only be pressed once) each time you start measurement. When the measurement is completed, a beep will sound and the locked number of tested papers will be displayed. If the number of papers cannot be locked and displayed, no points will be awarded.

Note: This project only shows part of the circuit and fulfills the basic design requirements and performance requirements required by the question.

Design idea: This project uses the NE555 chip to convert the capacitance (the paper sandwiched between the two-pole plates is a capacitive structure. Different amounts of paper are sandwiched, which is equivalent to different dielectric constants, so the capacitance is different) into a frequency signal, and the frequency signal is accurately measured through the FPGA. Get frequency information. Through the correspondence between paper-capacitance-frequency, the number of paper can be obtained.

Schematic analysis: The main circuit of this project is only the classic capacitance measurement circuit of NE555. The schematic diagram is as follows:

In the figure, J1 and J2 are connected to two different electrode plates. By switching different R4 or R5, the frequency signal can be adjusted to facilitate increasing the frequency interval of different papers. ~~~~

电源电路设计：

电路图如下图所示：

机械结构如下图所示：

调试过程：见视频链接，十分详细！

视频演示：由于视频较大，故上传到了bilibii。

视频链接：

https://www.bilibili.com/video/BV1ja411A72y/

源码附件和报告：见工程下载区