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connect-arduino-tessel.md

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#Arduino <-> Tessel communication

This is a tutorial for how to pass data back and forth between an Arduino and a Tessel.

The data is passed via a UART bridge. Arduino has the SoftwareSerial library for UART comm and Tessel has it's built in UART functions.

UART works through having TX (transmit) and RX (recieve) pins. A TX of one device is hooked up to the RX of another device like this:

  • Tessel TX <---> Arduino RX
  • Tessel RX <---> Arduino TX
  • Tessel GND <---> Arduino GND

##Step 1: Get an Arduino

The Arduino needs to operate at 3.3V. Some boards which operate at this voltage are:

Both the Seeeduino and the Crowduino can switch between 5V and 3.3V.

Arduino Uno

Arduino Unos send over signals at 5V and this will damage Tessel. If you are planning on using an Arduino Uno, you need to make a 5V to 3.3V level converter which shifts the 5V UART TX signal from the Arduino to 3.3V.

The UART TX coming from Tessel is at max 3.3V, but this will register as a digital "high" signal so it does not need to be boosted up to 5V.

##Step 2: Hook up the Arduino to the Tessel

There are 3 pins that need to be hooked up, UART TX, UART RX, and Ground.

In the code example, we're going to be using Arduino's SoftwareSerial on pins 10 and 11.

wiring an arduino to a tessel

  • Arduino Pin 10 (orange wire) <--> Tessel Port D, pin TX/G1
  • Arduino Pin 11 (white wire) <--> Tessel Port D, pin RX/G2
  • Arduino Ground (brown wire) <--> Tessel Ground

##Step 3: Program the Arduino

Run this code on the Arduino

#include <SoftwareSerial.h>
#define rxPin 10 // connect to TX of other device
#define txPin 11 // connect to RX of other device

SoftwareSerial tesselBridge =  SoftwareSerial(rxPin, txPin);

void setup()  
{
  // open serial port at 9600 baud
  Serial.begin(9600);
  Serial.println("Starting up...");
  
  // set the data rate for the SoftwareSerial port
  tesselBridge.begin(9600);
}

void loop() // run over and over
{
  if (tesselBridge.available())
    Serial.write(tesselBridge.read());
  if (Serial.available())
    tesselBridge.write(Serial.read());
}

##Step 4: Program Tessel

Make a folder for the code:

mkdir arduinoBridge;
cd arduinoBridge; touch uart.js;

Put this in the uart.js file.

var tessel = require('tessel');
var led1 = tessel.led[0].output(0);
var led2 = tessel.led[1].output(0);
var i = 0;

// baudrate must match the baudrate set in the Arduino file
uartBridge = tessel.port['D'].UART({baudrate: 9600}); 

uartBridge.on('data', function(data){
  // UART data is not packetized, so you will get the data 
  // buffer as the message is sent. This means that long
  // messages will be truncated as several events.
  
  var number = parseInt(data[0]) - 48; // convert hex to ascii to int
  console.log("got data", data, number);

  if (number == 1)
    led1.toggle();

  if (number == 2)
    led2.toggle();
});

// every 3 seconds write some data over to the arduino
setInterval(function(){
  uartBridge.write("Hi there "+i+"\n");
  i++;
}, 3000);

Run the code with tessel run uart.js, or if you want this to be persistent through power cycles, tessel push uart.js.

##Step 5: Test it You should be able to go into the Arduino console and see the blue and green LEDs on Tessel change as you enter a "1" or a "2".

terminal