Ultrasonic Reader

Ultrasonic.ino

#include <SoftwareSerial.h>
#include <Wire.h>
#include <NewPing.h>

#define TRIGGER_PIN  13  // Arduino pin tied to trigger pin on ping sensor.
#define ECHO_PIN     5  // Arduino pin tied to echo pin on ping sensor.
#define MAX_DISTANCE 100 // Maximum distance we want to ping for (in centimeters). Maximum sensor distance is rated at 400-500cm.

NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE); // NewPing setup of pins and maximum distance.
SoftwareSerial mySerial(2, 3); // RX, TX, Serial is needed to debug

unsigned int pingSpeed = 50; // How frequently are we going to send out a ping (in milliseconds). 50ms would be 20 times a second.
unsigned long pingTimer;     // Holds the next ping time.

int led = 7; //LED To indicate that the board is ON
int time = 0;

int request = 0; //What function was requested via i2c, only 0x02 at the moment

void setup(){
 // Open serial communications and wait for port to open:
  Serial.begin(115200);
  pinMode(led, OUTPUT);
  digitalWrite(led, 1);
  Wire.begin(3);                 // join i2c bus with address #3
  Wire.onRequest(requestEvent);  // reg request event, called when something is requested over i2c
  Wire.onReceive(receiveEvent);  // reg receive event, called when we receive something over i2c
   while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only   
   }
  Serial.println("Connected!!");
  pingTimer = millis();
}

void loop() // run over and over
{
  if (millis() >= pingTimer) {   // pingSpeed milliseconds since last ping, do another ping.
    pingTimer += pingSpeed;      // Set the next ping time.
    sonar.ping_timer(echoCheck); // Send out the ping, calls "echoCheck" function every 24uS where you can check the ping status.
  }
  // Do other stuff here, really. Think of it as multi-tasking.
}


void receiveEvent(int howMany)
{
  Serial.println("receive");
  char in[howMany];
  int counter = 0;
  while(Wire.available()>0) 
  {
    in[counter] = Wire.read();   // receive byte as a character
    counter++;
  }
  
  if (in[0] == 0x02){
   Serial.println("0x02 received");
   request = 2; //set request so that receive knows what to send
  }
  
  Serial.println(in[0]);
}

void requestEvent()
{
  if(request == 2){
    const uint8_t *c=(uint8_t *)(&time);  //point to the int with the round trip time as an array of 4 uint8_t
    
    Wire.write(c,4);  // respond with message of 4 bytes
    Serial.println(time);
  }
}

void echoCheck() { // Timer2 interrupt calls this function every 24uS where you can check the ping status.
  if (sonar.check_timer()) { // This is how you check to see if the ping was received.
    // Here's where you can add code.
    time = sonar.ping_result;
    //distance = sonar.ping_result / US_ROUNDTRIP_CM;
  }
}

UltrasonicReader.py

mport quick2wire.i2c as i2c
import time
import struct

address = 0x03 #Set the address to query

while True: #Just keep going!
    with i2c.I2CMaster() as bus:
        notdone=True
        while(notdone):
                time.sleep(0.1) #sleep just in case, there's a bug hiding somewhere that causes this to crash otherwise
                bus.transaction(i2c.writing_bytes(address,0x02)) #tell the 'duino we want to retreive a reading
                a,b,c,d = bus.transaction(i2c.reading(address,4))[0] #receive the reading
                ar = bytearray([a,b,c,d]) #put vals in a byte array, needed for the unpack later
                if not a==chr(0) or not b==chr(0) or not c==chr(0) or not d==chr(0): #make sure something was returned apart from zeroes
                        rtt = struct.unpack('<I',ar)[0] - 131072 #BUG! why is every value 131072 higher than it should be?
                                                                 #We use pythons struct.unpack to convert the byte array to an unsigned int
                        notdone=False #if we're here, we got a reading
                        print("Distance is %f CM" % (rtt/57)) #57 uS to travel 1CM, RTT
                else:
                        print("Not ready") #all zeroes returned
                        time.sleep(0.25) #lets sleep a little