Electronic – the cheapest way for two devices spaced less than 10 feet apart to communicate wirelessly with each other

communicationmicrocontrollerwireless

I'm building a musical instrument that comprises of two separate devices…one device is the master…has an accelerometer and a speaker. The master's buddy device also has an accelerometer.

When the buddy tilts, the buddy device interprets the accelerometer data and then sends a note to the master. The master plays the note using instrument voice 1.

The master, at the same time is processing it's own accelerometer information. Based on accelerometer data, it will play other notes using instrument voice 2.

If the user moves device one and then moves device two in special ways, a flourish will play.

My question is…taking into account the type/amount of data that I'm sending…essentially short control bytes, what would be the cheapest way for the two to communicate wirelessly?

–CLARIFICATION–
These devices ideally would be wireless and not tethered to each other. Also, these devices will be moved around freely so any line of sight method is less than ideal.

Best Answer

I'll assume you want to do this wireless, otherwise the solution is obvious.

I would go for infrared. The transmitter can be a small microcontroller sending a pair of bytes to an IR receiver module.

These receiver modules are tuned to a particular protocol. You can use an RC-5 module; RC-5 transmits 14-bit at a time using Manchester encoding. You can easily add a pair of bits to it, and define your own codes.

A 3 m range should not be a problem. I've used Vishay RC-5 receivers at 15 m range. At shorter distances you probably won't even have to direct the LED to the receiver. In a normal size room the signal will reflect off the walls.

A cheap RF solution is the RFM70:

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Less than 5 dollar at Digikey. That's far less than an Xbee.

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Easiest? Grab an Arduino and write a couple of lines of Python. Arduino's are incredibly easy to program, don't require any additional hardware to work with, and are quite popular. Python has a very straightforward serial library and is a breeze to write in.

Example Code

Python: Run this script as a service. I'm using Ubuntu, so this script will pop up a notification telling you when a button has been pressed on the Arduino.

#! /usr/bin/python

import serial
import pynotify

ser = serial.Serial('/dev/ttyUSB0', 9600)
while True:
  x = ser.read()
  if x == 'b':
    # Show notification
    n = pynotify.Notification("Arduino", "The button was pressed.")
    n.show()

Arduino:

void setup(){
  // Assuming button is active low and on pin 4
  pinMode(4, INPUT);
  Serial.begin(9600);
}

void loop(){
  if(digitalRead(4) == LOW){
    Serial.print('b');
  }
}

Electronic – arduino – the ‘best’ way of communicating with small microcontrollers/devices

Bluetooth LE (Low Energy) is actually perfect for this type of application. It's meant for low power and low bandwidth communication needs, where each device only needs to send very small bursts of information periodically. It's also very highly optimized to run off of coin cell batteries so you might not need AC adapters if the sensor's duties are simple enough. We recently did a project that used lots of Bluetooth LE beacons and each one lasted for about 2 months off of a coin cell battery.

The hardware we used was already built for us but there are BLE solutions for the Arduino: http://www.adafruit.com/products/1697

Best part is you can use it with any device that has Bluetooth 4.0! (iPhone, Android phone, BT 4.0 dongle). And you'd only need one receiver since Bluetooth is already highly optimized to share the RF spectrum.

I used this book to get acquainted with BLE, it was pretty useful (very detailed but you can skim through what you need): http://amzn.com/013288836X

One important thing to note if you want to use Android: There was a rather annoying bug with its BLE implementation so you need the latest Android (4.4.3) to get the best results. Although, it only affects you if you have tons (over 2000) unique BLE device IDs floating around (which can happen if some devices want to rotate their MAC address for privacy reasons).

Best Answer

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