用RPI 來實作一個簡易的示波器

大概的構想是  :  RPI  + Arduino

Arduino 因為有類比輸入....很方便.....而且是12 bit....負責去讀取 類比資料

然後RPI  透過  usb 轉 Serial 的方式去和 Arduino 要資料 ...

然後在RPI 上面畫 line plot.....



在RPI  部分....

我找個一個sample  ->  Ref 1:

他會一直去更新圖表....這就是我們要的....


看了程式...發覺在 class DataGen 的  next


self.data = [self.datagen.next()]  ->

 def next(self):
        self._recalc_data()   ->

 def _recalc_data(self):

        delta = random.uniform(-0.5, 0.5)

        r = random.random()

        if r > 0.9:

            self.data += delta * 15

        elif r > 0.8:

            # attraction to the initial value

            delta += (0.5 if self.init > self.data else -0.5)

            self.data += delta

        else:

            self.data += delta

  這裡他是用random 的方式去產生資料 ...然後把資料insert 到  self.data

 所以我們只需要改這裡即可.....

可以參考Ref 2

import serial

//write 方面

ser.write(output)
ser.flush()

//read  方面
x=ser.readline()

print x

import serial
          
      
           ser = serial.Serial(
              
               port='/dev/ttyUSB0',
               baudrate = 9600,
               parity=serial.PARITY_NONE,
               stopbits=serial.STOPBITS_ONE,
               bytesize=serial.EIGHTBITS,
               timeout=1
           )
           counter=0
          
      
           while 1:
               x=ser.readline()

在 Arduino 部分...這部分比較簡單....大概就是 serial 傳輸加上   讀analogy  value....

int  firstSensor =0;
void setup()
{
  // start serial port at 9600 bps:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }

}

void loop()
{

 if (Serial.available() > 0) {

    // get incoming byte:
    //inByte = Serial.read();
    // read first analog input, divide by 4 to make the range 0-255:
    firstSensor = analogRead(A0)/4;
      // send sensor values:
    Serial.write(firstSensor);
   
  }
}

這邊有個例子:

你可以寫兩支程式，一支在 Arduino 上跑，另一支在 PC 上跑，讓 Arduino 跟 PC 端的程式彼此通訊，建立互動。底下有個簡單的範例:

Arduino 這端的程式 (potentiometer.pde) 不斷地讀取 Sensor 並把資料寫到 Serial port (以位元組的格式寫出):






01
int potPin = 3; // potentiometer pin




02





03
void setup() {




04
  Serial.begin(9600);




05
}




06





07
void loop() {




08
  int sensorValue = analogRead(potPin);




09
  Serial.println(sensorValue/4, BYTE);




10
  delay(150);




11
}





而 PC 端的 processing 程式 (pRead.pde) 則是把資料從 PC 端的 Serial port 讀取進來:





view source



print?




01
import processing.serial.*;




02





03
Serial myPort;  // The Serial port




04





05
void setup()




06
{




07
  // 開啟 Serial port，通訊速率為 9600 bps




08
  String portName = "COM4";




09
  myPort = new Serial(this, portName, 9600);




10
}




11





12
void draw()




13
{




14
  // 檢查 Serial port 是否有資料進來




15
  if ( myPort.available() > 0) {




16
    // 讀取進來的 byte




17
    int incomingByte = myPort.read();




18
     




19
    // 印出收到的資料




20
    println(incomingByte);




21
  }




22
}

ps :  matplotlib 安裝

git clone https://github.com/matplotlib/matplotlib
cd matplotlib
python setup.py build
sudo python setup.py ins

ps :  arduino println()

Description

Prints data to the serial port as human-readable ASCII text followed by a carriage return character (ASCII 13, or '\r') and a newline character (ASCII 10, or '\n'). This command takes the same forms as Serial.print().

Syntax

Serial.println(val) 
Serial.println(val, format)

Parameters
val: the value to print - any data typetall

example :

analogValue = analogRead(0);

  // print it out in many formats:
  Serial.println(analogValue);       // print as an ASCII-encoded decimal
  Serial.println(analogValue, DEC);  // print as an ASCII-encoded decimal
  Serial.println(analogValue, HEX);  // print as an ASCII-encoded hexadecimal
  Serial.println(analogValue, OCT);  // print as an ASCII-encoded octal
  Serial.println(analogValue, BIN);  // print as an ASCII-encoded binary

write()

Description

Writes binary data to the serial port. This data is sent as a byte or series of bytes; to send the characters representing the digits of a number use the print() function instead.

Syntax

Serial.write(val)
Serial.write(str)
Serial.write(buf, len)

Arduino Mega also supports: Serial1, Serial2, Serial3 (in place of Serial)

Parameters

val: a value to send as a single byte

str: a string to send as a series of bytes

buf: an array to send as a series of bytes

len: the length of the buffer

Reference 1  : https://github.com/eliben/code-for-blog/blob/master/2008/wx_mpl_dynamic_graph.py

Reference 2  : http://owenson.me/build-your-own-quadcopter-autopilot/pyserver.py.txt

Reference 3 : http://www.instructables.com/id/Read-and-write-from-serial-port-with-Raspberry-Pi/

Reference 4 : http://coopermaa2nd.blogspot.tw/2011/02/arduino-serial-library.html