*採集數據&繪製曲線¶

實際拿裝置與電子秤來測(如圖)
紀錄FSR值與壓力大小(g)
(裝置盡量放電子秤正中央，記得歸零)¶

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按照紀錄的數值可於excel中繪製曲線圖
PRESSURE = [250, 500, 1000, 1500, 2000]
FSR = [50, 250, 400, 480, 600]¶

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*Curve fitting¶

自行Google "python curve fitting教學"
參考資料： https://www.796t.com/content/1546862273.html¶

#encoding=utf-8  
import numpy as np
import matplotlib.pyplot as plt

#定義x、y散點座標
num = [0, 250, 500, 1000, 1500, 2000]
x = [0, 50, 250, 400, 480, 600]
y = np.array(num)

#用5次多項式擬合
f1 = np.polyfit(x, y, 5)
p1 = np.poly1d(f1)
print(p1)

#也可使用yvals=np.polyval(f1, x)
yvals = p1(x)  #擬合y值

#繪圖
plot1 = plt.plot(x, y, 's',label='original values')
plot2 = plt.plot(x, yvals, 'r',label='polyfit values')
plt.xlabel('x')
plt.ylabel('y')
plt.legend(loc=4) #指定legend的位置右下角
plt.title('polyfitting')
plt.show()
plt.savefig('test.png')

執行完程式會得到類似下面的效果：
x-axis：FSR value
y-axis：壓力(g)¶

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*壓力計設計(韌體)¶

  int fsr = 0;
  double pressure = 0;

  fsr = analogRead(FSR_pin);
  pressure = 0.0000009 * pow(x, 3) + 0.003137 * pow(x, 2) + 1.05 * x + 76.28;

  //Serial.printf("FSR = %d\n",fsr);
  //Serial.printf("PRESSURE = %.6f\n",pressure );

  for(int d = 0; d < 10; d++){
    tft.fillRect((DISP_X + 60) + (d * 11), DISP_Y + 185, 10, 10, TFT_SILVER);
    if(pressure > d * 100){
      tft.fillRect((DISP_X + 60) + (d * 11), DISP_Y + 185, 10, 10, TFT_GREEN);
    }
  }