使用Python的Pyserial将字符发送到Arduino串口

我已经设置了一个Arduino来接收'S'字节时发送数据 . 这适用于Arduino串行监视器 . 但是，我正在使用Pyserial联系串口来绘制Python上的数据 . 这是我的Arduino草图，以明确我的意思：

#include <eHealth.h>


unsigned long time;
unsigned long interval = 8;
byte serialByte;

// The setup routine runs once when you press reset:
void setup() {
  Serial.begin(9600);  
}

// The loop routine runs over and over again forever:
void loop() {
  if(Serial.available()>0){
    serialByte = Serial.read();
    if(serialByte == 'S'){  
      while(1){
        float ECG = eHealth.getECG();
        time = time + interval;
        Serial.print(time);
        Serial.print(" ");
        Serial.print(ECG, 3); 
        Serial.println("");

        if(Serial.available()>0){
          serialByte = Serial.read();
          if (serialByte == 'F') break;
        }
      }
    }
  }
  delay(interval);
}

正如我所说，这很好 . 但是当我尝试这个时在Python上：

import serial
ser = serial.Serial('/dev/tty.usbmodem1411', 9600)
ser.write(bytearray('S','ascii'))

或这个：

import serial
ser = serial.Serial('/dev/tty.usbmodem1411', 9600)
ser.write('S')

arduino由于某种原因没有收到它，并且数据不会通过串口流到Python . 我不知道这个问题 . 正如您所看到的，我已尝试转换为字节，但仍然无法正常工作 .

这是我的完整Python代码：

from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg, NavigationToolbar2QTAgg
import matplotlib.figure as mfig
import PyQt4.QtGui as gui, PyQt4.QtCore as core
import collections
import time
import random

import serial
ser = serial.Serial('/dev/tty.usbmodem1411', 9600)
ser.write('S')


refreshMillis = 8
N = 200
xs = collections.deque(maxlen=N)
ys = collections.deque(maxlen=N) 

app = gui.QApplication([])

fig = mfig.Figure()
canvas = FigureCanvasQTAgg(fig)

ax = fig.add_subplot(111)
ax.set_ylim([0,5])
# ax.title("Arduino Electrocardiogram")
ax.set_xlabel("Time (ms)")
ax.set_ylabel("Voltage (V)")
line2D, = ax.plot(xs,ys)
canvas.show()


def process_line():
    line = ser.readline()
    data = map(float,line.split(" "))
    xs.append(data[0])
    ys.append(data[1])
    line2D.set_data(xs,ys)
    print data
    xmin, xmax = min(xs),max(xs)
    if xmin == xmax:
        ax.set_xlim([xmin,xmin+1])
    else:
        ax.set_xlim([xmin,xmax])
    canvas.draw()

    zipString = zip(xs,ys)
    f = open("plot_store","w")
    for line in zipString:
        f.write(" ".join(str(x) for x in line) + "\n")
    f.close()




timer = core.QTimer()
timer.timeout.connect(process_line)
timer.start(refreshMillis)

app.exec_()

ser.flush()
ser.close()