【Lanzhou University】Paper counting display device

The question requirements are the same as question F in the 2019 National College Student Electronic Design Competition.

The paper counting display device is divided into a data collection part and a data processing and display part. The data collection part uses a precisely processed 50mm×50mm×3mm copper plate as the capacitor plate; an acrylic plate is used, and the copper plate is fixed on two precision-drilled acrylic plates with epoxy resin AB glue. The four corners of the plate have The screws are fixed to ensure that the facing area of ​​the copper plate will not change due to placement errors each time the paper to be tested is clamped. The data processing and display part consists of a self-built AD8606 amplifier circuit and STM32F103 microcontroller. When adding paper, the capacitance change between the electrode plates undergoes AD sampling, average filtering algorithm, third-order polynomial fitting, and least squares fitting, so that the sampling value forms a linear relationship with the number of papers. After each test paper is added, the number of papers is displayed on the OLED display.