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soundanalogous/_Ping I2C Johnny Five backpack.md

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Last active February 15, 2021 16:01
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README.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.

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.

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.

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.

Known issues

At the moment you get a bit of lag creep in after a while. I think this might be something to do with the I2C send buffer but will dig in more.

Todo

  • Track down this lag thing
  • Try this on a raw ATTINY using avr-gcc etc so no arduino deps
  • Figure out how this comes back into Johnny-five as backpack
Raw
ping.ino
#define I2C_SENSOR_ADDRESS 0x27
#define REGISTER_MAP_SIZE 2
#define PING_PIN 4
#define PING_FREQUENCY 150 // milliseconds between pings
// Uncomment to use ATMEGA
//#include <Wire.h>
// Uncomment to use ATTINY
#include <TinyWireS.h>
#include <avr/power.h>
// this won't work on ATTINY
#ifndef _DEBUG
#define _DEBUG false
#endif
byte register_map[REGISTER_MAP_SIZE];
int32_t duration; // duration of the ping
int32_t last_ping_time = 0;
int32_t ping_freq = PING_FREQUENCY;
void setup(){
// Use Wire commands for ATMEGA
// Wire.begin(I2C_SENSOR_ADDRESS);
// Wire.onRequest(requestData);
// ATTINY
// 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);
#if _DEBUG
Serial.begin(9600);
Serial.println("Ping Sensor I2C");
#endif
}
void loop(){
get_distance();
// USE this for ATTINY as you can't use delay
TinyWireS_stop_check();
// Use this for ATMEGA
// delay(20);
}
void get_distance() {
if ((millis() - last_ping_time) > ping_freq) {
pinMode(PING_PIN, OUTPUT);
digitalWrite(PING_PIN, LOW);
delayMicroseconds(2);
digitalWrite(PING_PIN, HIGH);
delayMicroseconds(5);
digitalWrite(PING_PIN, LOW);
pinMode(PING_PIN, INPUT);
duration = pulseIn(PING_PIN, HIGH);
register_map[0] = duration >> 8; // msb
register_map[1] = duration & 0xFF; //LSB
#if _DEBUG
Serial.println(duration);
#endif
last_ping_time = millis();
}
}
void requestData(){
// ATMEGA cat write out a buffer
// Wire.write(register_map, REGISTER_MAP_SIZE);
// ATTINY you need to do a send of each register individually.
TinyWireS.send(register_map[0]);
TinyWireS.send(register_map[1]);
#if _DEBUG
Serial.print("rm: ");
Serial.print(register_map[0]);
Serial.print(" ");
Serial.print(register_map[1]);
Serial.println();
#endif
}
Raw
ping.js
var events = require("events"),
util = require("util");
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: 110, // an optimium period to poll the sensor on i2c.
};
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
Raw
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();
});
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