_Ping I2C Johnny Five backpack.md

Building an ultrasonic sensor backpack

Note: This is a bit of a scratch to see what's involved in getting the ping sensor to work as an I2C backpack.

Acknowledgements

• Jeff Hoeffs [http://github.com/soundanalogous](Sound Analogous) for guidance on using interrupts to do the time measurement on the ATTINY and [https://gist.github.com/soundanalogous/e94c6ebbc457b98b8383](providing a good example to work from)
• [http://github.com/rwaldron](Rick Waldron) for support of the backpack idea and keeping me moving. ;)

Dependencies.

I did this on a Trinket as that's what I had to hand to make programming a bit faster. If you use a trinket you will need the custom arduino. Check out the Adafruit Trinket info https://learn.adafruit.com/introducing-trinket/introduction

You also need a custom form of the TinyWireS library that manages sending multiple registers on one read request (the default implementation doesn't do this and locks up the buffer). This can be had here: https://github.com/Godziluu/TinyWire/ Do the usual thing and install into libraries folder of your sketch directory.

If you want to debug then you'll need a special form of Software serial - called [http://gammon.com.au/Arduino/SendOnlySoftwareSerial.zip](SoftwareSerialSendOnly - note Zip) which does what you'd expect and only uses a single pin (handy on an ATTINY).

Files

ping.ino can work on both an ATTiny85 and standard Arduino. It sets up as an I2C peripheral device. However, ATTINY can't use the wire library so has to use tiny wire. Read the code for the places to comment / uncomment to get this to work.

includes.h provides the #if hacks for arduino

ping.js A hack of the existing ping.js library in J5 using that as the base. Removed things that were no longer necessary and migrated relevant calls to I2C rather than pin manipulation.

pingtest.js is simply a demo to get it spitting out the data events. Note that this is using a hardcoded port just to eliminate any confusion across devices (I was using an arduino at one point so was getting port conflicts - easier to be explicit).

Usage

• Arduino requires only standard firmata
• Wire up the Trinket / ATTINY85 so that the ping trigger / echo is on pin 4.
• Wire up VCC and GND, then SDA and SCL to the arduino master.

Power everything up then run your sketch.

npm install johnny-five
node ping-test.js

You should get an output of distance in CM.

Current status

• Lag issues have been resolved and were due to pulsein blocking
• Speed is viable at 100msec pin intervals on an ATTINY85 no problems.
• Tool chain is very clutzy due to issues with inotool not understanding attiny
• Ranging is accurate (to the level of accuracy of the actual sensor at least).

Known issues

Some kind of issue with I2C whereby if the JS application is stopped then restarted but the Backpack isn't reset then Firmata times out and won't connect.

Todo

• Track down this lag thing
• Fix issue with timing delay causing inflated timings.
• Fix issue with the firmata timeout.
• Get ATTINY using avr-gcc etc so no arduino deps at all
• clean up the schmozzle that is the inotool build chain with attiny
• Figure out how this comes back into Johnny-five as backpack with rwaldron

includes.h

#include <avr/interrupt.h>

#if defined( __AVR_ATtiny85__ )
    #include <TinyWireS.h>
    #include <avr/power.h>

    #include <SendOnlySoftwareSerial.h>

    SendOnlySoftwareSerial Serial(3);
  
    #define PING_PIN 4
#else
    #include <Wire.h>
    #define PING_PIN 12
#endif

#ifndef _DEBUG
    #define _DEBUG false
#endif

#ifndef _VDEBUG
    #define _VDEBUG false
#endif

ping.ino

#define I2C_SENSOR_ADDRESS  0x27
#define REGISTER_MAP_SIZE 2

#include "includes.h"

#if _VDEBUG
    #define PING_FREQUENCY 1000 // milliseconds between pings
#else
    #define PING_FREQUENCY 100 // go much slower so we can see wtf is going on
#endif

byte register_map[REGISTER_MAP_SIZE];

volatile int32_t duration; // duration of the ping
int32_t last_ping_time = 0; // last time the ping occurred in ms
int32_t ping_freq = PING_FREQUENCY;
int32_t ping_emit_time = 0;  // time the ping was emitted in us

bool pinging = false; // used to determine when we're pinging


// Interrupt vector for external interrupt on pin PCINT7..0
// This will be called when any of the pins D0 - D4 on the trinket change
// or pins D8 - D13 on an Arduino Uno change.

// the ping pin will flip HIGH at the point when the pulse has completed
// and timing should begin, it will then flip LOW once the sound wave is received
// so we need to detect both of these states

ISR(PCINT0_vect) {
    
    if (digitalRead(PING_PIN) == HIGH) {
        pinging = true;
        ping_emit_time = micros();
    } else { 
        duration = micros() - ping_emit_time;
    }
}

void setup() {

#if defined( __AVR_ATtiny85__ )
    // Set prescaler so CPU runs at 16MHz
    if (F_CPU == 16000000) clock_prescale_set(clock_div_1);

    // Use TinyWire for ATTINY
    TinyWireS.begin(I2C_SENSOR_ADDRESS);
    TinyWireS.onRequest(requestData);

#else
    Wire.begin(I2C_SENSOR_ADDRESS);
    Wire.onRequest(requestData);
#endif

#if _DEBUG
    Serial.begin(9600);
    Serial.println("Ping Sensor I2C");
#endif
}


void loop() {

    get_distance();

#if defined( __AVR_ATtiny85__ )
    // USE this for ATTINY as you can't use delay
    TinyWireS_stop_check();
#else
    delay(20);
#endif
}

void disablePCInterrupt() {
    // disable all interrupts temporarily
    cli();

    // disable pin change interrupt
    PCMSK &= ~_BV(PCINT4);

    // clear pin change interrupt flag register
#if defined( __AVR_ATtiny85__ )
    GIFR &= ~_BV(PCIF);
#else
    PCIFR &= ~_BV(PCIF2);
#endif
    // re-enable all interrupts
    sei();
}

void enablePCInterrupt() {
    // disable all interrupts temporarily
    cli();

    // enable pin change interrupt on PB4 (D4 on Trinket, D12 on Uno)
    PCMSK |= _BV(PCINT4);

    // enable pin change interrupt 0
#if defined( __AVR_ATtiny85__ )
    GIMSK |= _BV(PCIE);
#else
    PCICR |= _BV(PCIE0);
#endif
    // re-enable all interrupts
    sei();
}

void get_distance() {

    if ((millis() - last_ping_time) > ping_freq) {

        // disable interrupt while pinMode is OUTPUT
        // not sure if this is actually necessary, but just
        // playing it safe to avoid false interrupt when
        // pin mode is OUTPUT
        disablePCInterrupt();

    #if _VDEBUG        
        //Serial.print("D: ");
        //Serial.println(duration);
        Serial.print("CM:");
        Serial.println((long)duration / 29 / 2);
    #endif
    
        pinging = false;

        pinMode(PING_PIN, OUTPUT);
        digitalWrite(PING_PIN, LOW);
        delayMicroseconds(2);
        digitalWrite(PING_PIN, HIGH);
        delayMicroseconds(5);
        digitalWrite(PING_PIN, LOW);

        pinMode(PING_PIN, INPUT);

        // we'll use a pin change interrupt to notify when the
        // ping pin changes rather than being blocked by
        // Arduino's built-in pulseIn function
        enablePCInterrupt();

        last_ping_time = millis();
    }
}

void requestData() {

    register_map[0] = duration >> 8; // msb
    register_map[1] = duration & 0xFF; //LSB

#if defined( __AVR_ATtiny85__ )
    // ATTINY you need to do a send of each register individually.
    TinyWireS.send(register_map[0]);
    TinyWireS.send(register_map[1]);
#else
    // ATMEGA cat write out a buffer
    Wire.write(register_map, REGISTER_MAP_SIZE);
#endif

#if _DEBUG
    Serial.print("rm: ");
    Serial.print(register_map[0]);
    Serial.print(" ");
    Serial.print(register_map[1]);
    Serial.println();
#endif
}

ping.js

var events = require("events"),
  util = require("util");
//  within = require("./mixins/within"),
//  __ = require("./fn");

var priv = new Map();

/**
 * Ping
 * @param {Object} opts Options: addr freq
 */

function Ping(opts) {

  if (!(this instanceof Ping)) {
    return new Ping(opts);
  }

  var last = null;

  this.addr = opts && opts.addr || 0x27;
  this.freq = opts.freq || 100;
  this.board = opts.board || null;

  var state = {
    value: 0
  };

  // Private settings object
  var settings = {
    addr: this.addr,
    value: this.board.io.HIGH,
    readBytes: 2, // the duration that comes off the ping is a 16 bit int
    pingFreq: 210, // whatever the required frequency is, go a bit less
  };

  this.board.io.setMaxListeners(100);

    this.board.io.i2cConfig();
  // Interval for polling pulse duration as reported in microseconds
  setInterval(function() {
    this.board.io.i2cReadOnce(settings.addr, settings.readBytes, function(data) {
      state.value = (data[0] << 8) + data[1];
    });
  }.bind(this), settings.pingFreq);

  // Interval for throttled event
  setInterval(function() {
    var err = null;

    if (!state.value) {
      return;
    }

    // The "read" event has been deprecated in
    // favor of a "data" event.
    this.emit("data", err, state.value);

    // If the state.value for this interval is not the same as the
    // state.value in the last interval, fire a "change" event.
    if (state.value !== last) {
      this.emit("change", err, state.value);
    }

    // Store state.value for comparison in next interval
    last = state.value;

    // Reset samples;
    // samples.length = 0;
  }.bind(this), this.freq);

  Object.defineProperties(this, {
    value: {
      get: function() {
        return state.value;
      }
    },
    // Based on the round trip travel time in microseconds,
    // Calculate the distance in inches and centimeters
    inches: {
      get: function() {
        return +(state.value / 74 / 2).toFixed(2);
      }
    },
    in: {
      get: function() {
        return this.inches;
      }
    },
    cm: {
      get: function() {
        return +(state.value / 29 / 2).toFixed(3);
      }
    }
  });

  priv.set(this, state);
}

util.inherits(Ping, events.EventEmitter);

module.exports = Ping;

//http://protolab.pbworks.com/w/page/19403657/TutorialPings

pingtest.js

var five = require("johnny-five");
var ping = require('./ping.js');

var board = five.Board({port: '/dev/ttyACM0'});

board.on('ready', function() {

    var p = new ping({
        addr: 0x27,
        freq: 300,
        board: this,
    });

    p.on("data", function(){
        console.log(this.cm);
    });
});

board.on('error', function(err) {
    console.log(err);
    process.exit();
});

test.js

var five = require("johnny-five");

var board = five.Board({port: '/dev/ttyACM0'})

board.on("ready", function() {

    this.i2cConfig();

    setInterval(function() {
        this.i2cReadOnce(0x27, 2, function(data) {
            console.log(data);
            console.log("tranformed: " + ((data[0] << 8) + data[1]));
        });
    }.bind(this), 1000);


});