Blog Archives

Playing with Raspberry Pi, Arduino, NodeMcu and MQTT

These days I’m playing with IoT. Today I want to use MQTT protocol to comunicate between different devices. First I’ve start a mqtt broker in my Laptop. For testing I’ll use mosquitto server. In production we can use RabbitMQ or even a 3party server such as iot.eclipse.org or even Amazon’s IoT service.

The idea is emit one value with one device, and listen this value whit the rest of devices and perform one action depending on that value. For example I will use one potentiometer connected to on NodeMcu micro controller.

This controller will connect to the mqtt broker and will emit the value of the potentiometer (reading the analog input) into one topic (called “potentiometer”). We can code our NodeMcu with Lua but I’m more confortable with C++ and Arduino IDE. First I need to connect to my Wifi and then connect to broker and start emmiting potentiometer’s values

#include <PubSubClient.h>
#include <ESP8266WiFi.h>

// Wifi configuration
const char* ssid = "MY_WIFI_SSID";
const char* password = "my_wifi_password";

// mqtt configuration
const char* server = "192.168.1.104";
const char* topic = "potentiometer";
const char* clientName = "com.gonzalo123.nodemcu";

int value;
int percent;
String payload;

WiFiClient wifiClient;
PubSubClient client(wifiClient);

void wifiConnect() {
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("WiFi connected.");
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  if (client.connect(clientName)) {
    Serial.print("Connected to MQTT broker at ");
    Serial.print(server);
    Serial.print(" as ");
    Serial.println(clientName);
    Serial.print("Topic is: ");
    Serial.println(topic);
  }
  else {
    Serial.println("MQTT connect failed");
    Serial.println("Will reset and try again...");
    abort();
  }
}

void mqttReConnect() {
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect(clientName)) {
      Serial.println("connected");
      client.subscribe(topic);
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      delay(5000);
    }
  }
}

void setup() {
  Serial.begin(9600);
  client.setServer(server, 1883);
  wifiConnect();
  delay(10);
}

void loop() {
  value = analogRead(A0);
  percent = (int) ((value * 100) / 1010);
  payload = (String) percent;
  if (client.connected()) {
    if (client.publish(topic, (char*) payload.c_str())) {
      Serial.print("Publish ok (");
      Serial.print(payload);
      Serial.println(")");
    } else {
      Serial.println("Publish failed");
    }
  } else {
    mqttReConnect();
  }

  delay(200);
}

Now we will use another Arduino (with a ethernet shield).

We’ll move one servomotor depending to NodeMcu’s potentiomenter value. This Arduino only needs to listen to MQTT’s topic and move the servo.

#include <SPI.h>
#include <Servo.h>
#include <Ethernet.h>
#include <PubSubClient.h>

#define SERVO_CONTROL 9
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

Servo servo;
EthernetClient ethClient;

// mqtt configuration
const char* server = "192.168.1.104";
const char* topic = "potentiometer";
const char* clientName = "com.gonzalo123.arduino";

PubSubClient client(ethClient);

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] angle:");

  String data;
  for (int i = 0; i < length; i++) {
    data += (char)payload[i];
  }

  double angle = ((data.toInt() * 180) / 100);
  constrain(angle, 0, 180);
  servo.write((int) angle);
  Serial.println((int) angle);
}

void mqttReConnect() {
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    if (client.connect(clientName)) {
      Serial.println("connected");
      client.subscribe(topic);
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      delay(5000);
    }
  }
}

void setup()
{
  Serial.begin(9600);
  client.setServer(server, 1883);
  client.setCallback(callback);
  servo.attach(SERVO_CONTROL);
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
  }

  delay(1500); // Allow the hardware to sort itself out
}

void loop()
{
  if (!client.connected()) {
    mqttReConnect();
  }
  client.loop();
}

Finally we’ll use one Raspberry Pi with a Sense Hat and we’ll display with its led matrix different colors and dots, depending on the NodeMcu’s value. In the same way than the Arduino script here we only need to listen to the broker’s topic and perform the actions with the sense hat. Now with Python

import paho.mqtt.client as mqtt
from sense_hat import SenseHat

sense = SenseHat()
sense.clear()
mqttServer = "192.168.1.104"

red = [255, 0, 0]
green = [0, 255, 0]
yellow = [255, 255, 0]
black = [0, 0, 0]

def on_connect(client, userdata, rc):
    print("Connected!")
    client.subscribe("potentiometer")

def on_message(client, userdata, msg):
    value = (64 * int(msg.payload)) / 100
    O = black
    if value < 21:
        X = red
    elif value < 42:
        X = yellow
    else:
        X = green

    sense.set_pixels(([X] * value) + ([O] * (64 - value)))

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect(mqttServer, 1883, 60)
client.loop_forever()

The hardware:

  • 1 Arduino Uno
  • 1 NodeMCU (V3)
  • 1 potentiometer
  • 1 Servo (SG90)
  • 1 Raspberry Pi 3 (with a Sense Hat)
    • Source code is available in my github.

Arduino and Raspberry Pi working together

Basically everything we can do with Arduino it can be done also with a Raspberry Pi (an viceversa). There’re things that they’re easy to do with Arduino (connect sensors for example). But another things (such as work with REST servers, databases, …) are “complicated” with Arduino and C++ (they are possible but require a lot of low level operations) and pretty straightforward with Raspberry Pi and Python (at least for me and because of my background)

With this small project I want to use an Arduino board and Raspberry Pi working together. The idea is blink two LEDs. One (green one) will be controlled by Raspberry Pi directly via GPIO and another one (red one) will be controlled by Arduino board. Raspberry Pi will be the “brain” of the project and will tell to Arduino board when turn on/off it’s led. Let’s show you the code.

import RPi.GPIO as gpio
import serial
import time
import sys
import os

def main():
    gpio.setmode(gpio.BOARD)
    gpio.setup(12, gpio.OUT)

    s = serial.Serial('/dev/ttyACM0', 9600)
    status = False

    while 1:
        gpio.output(12, status)
        status = not status
        print status
        s.write("1\n" if status else "0\n")
        time.sleep(1)

if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        print 'Interrupted'
        gpio.cleanup()
        try:
            sys.exit(0)
        except SystemExit:
            os._exit(0)

As we can see the script is a simple loop and blink led (using pin 12) with one interval of one second. Our Arduino board is connected directly to the Raspberry Pi via USB cable and we send commands via serial interface.

Finally the Arduino program:

#define LED  11

String serialData = "";
boolean onSerialRead = false; 

void setup() {
  // initialize serial:
  Serial.begin(9600);
  serialData.reserve(200);
}

void procesSerialData() {
  Serial.print("Data " + serialData);
  if (serialData == "1") {    
    Serial.println(" LED ON");
    digitalWrite(LED, HIGH);
  } else {
    Serial.println(" LED OFF");
    digitalWrite(LED, LOW);
  }
  serialData = "";
  onSerialRead = false;
}

void loop() {
  if (onSerialRead) {
    procesSerialData();
  }
}

void serialEvent() {
  while (Serial.available()) {
    char inChar = (char)Serial.read();
    if (inChar == '\n') {
      onSerialRead = true;
    } else {
      serialData += inChar;
    }
  }
}

Here our Arduino Board is listening to serial interface (with serialEvent) and each time we receive “\n” the main loop will turn on/off the led depending on value (1 – On, 0 – Off)

We can use I2C and another ways to connect Arduino and Raspberry Pi but in this example we’re using the simplest way to do it: A USB cable. We only need a A/B USB cable. We don’t need any other extra hardware (such as resistors) and the software part is pretty straightforward also.

Hardware:

  • Arduino UNO
  • Raspberry Pi 3
  • Two LEDs and two resistors

Code in my github account

Control humidity with a Raspberry Pi and IoT devices

I’ve got a Wemo switch and a BeeWi temperature/humidity sensor. I’ve use them in previous projects. Today I want a control humidity level in a room. The idea is switch on/off a dehumidifier (plugged to Wemo switch) depending on the humidity (from BeeWi sensor). Let’s start.

I’ve got one script (node) that reads humidity from the sensor (via BTLE)

#!/usr/bin/env node
noble = require('noble');

var status = false;
var address = process.argv[2];

if (!address) {
    console.log('Usage "./reader.py <sensor mac address>"');
    process.exit();
}

function hexToInt(hex) {
    var num, maxVal;
    if (hex.length % 2 !== 0) {
        hex = "0" + hex;
    }
    num = parseInt(hex, 16);
    maxVal = Math.pow(2, hex.length / 2 * 8);
    if (num > maxVal / 2 - 1) {
        num = num - maxVal;
    }

    return num;
}

noble.on('stateChange', function(state) {
    status = (state === 'poweredOn');
});

noble.on('discover', function(peripheral) {
    if (peripheral.address == address) {
        var data = peripheral.advertisement.manufacturerData.toString('hex');
        console.log(Math.min(100,parseInt(data.substr(14, 2),16)));
        noble.stopScanning();
        process.exit();
    }
});

noble.on('scanStop', function() {
    noble.stopScanning();
});

setTimeout(function() {
    noble.stopScanning();
    noble.startScanning();
}, 3000);

Now I’ve got another script to control the switch. A Python script using ouimeaux library

#!/usr/bin/env python
from ouimeaux.environment import Environment
from subprocess import check_output
import sys
import os

threshold = 3

def action(switch):
    humidity = int(check_output(["%s/reader.js" % os.path.dirname(sys.argv[0]), sensorMac]))
    if "Switch1" == switch.name:
        botton = expected - threshold
        isOn = False if switch.get_state() == 0 else True
        log = ""

        if isOn and humidity < botton:
            switch.basicevent.SetBinaryState(BinaryState=0)
            log = "humidity < %s Switch to OFF" % botton
        elif not isOn and humidity > expected:
            switch.basicevent.SetBinaryState(BinaryState=1)
            log = "humidity > %s Switch to ON" % expected

        print "Humidity: %s Switch is OK (%s) %s" % (humidity, 'On' if isOn else 'Off', log)

if __name__ == '__main__':
    try:
        sensorMac = sys.argv[1]
        mySwitch = sys.argv[2]
        expected = int(sys.argv[3])
    except:
        print 'Usage "./dehumidifier.py <sensorMac> <switch name> <expected humidity>"'
        sys.exit()

    env = Environment(action)
    env.start()
    env.discover(seconds=3)

And that’s all. Now I only need to configure my Raspberry Pi’s crontab and run the script each minute

*/1 * * * *     /mnt/media/projects/hum/dehumidifier.py ff:ff:ff:ff:ff:ff Switch1 50

Project is available in my github account.

Nowadays I’m involved with Arduino and iot, so I wand to do something similar with cheaper Arduino stuff.

Playing with RabbitMQ (part 2). Now with Python

Do you remember the las post about RabbitMQ? In that post we created a small wrapper library to use RabbitMQ with node and PHP. I also work with Python and I also want to use the same RabbitMQ wrapper here. With Python there’re several libraries to use Rabbit. I’ll use pika.

The idea is the same than the another post. I want to use queues, exchanges and RPCs. So let’s start with queues:

We can create a queue receiver called ‘queue.backend’

from rabbit import builder

server = {
    'host': 'localhost',
    'port': 5672,
    'user': 'guest',
    'pass': 'guest',
}

def onData(data):
    print data['aaa']

builder.queue('queue.backend', server).receive(onData)

and emit messages to the queue

from rabbit import builder

server = {
    'host': 'localhost',
    'port': 5672,
    'user': 'guest',
    'pass': 'guest',
}

queue = builder.queue('queue.backend', server)

queue.emit({"aaa": 1})
queue.emit({"aaa": 2})
queue.emit({"aaa": 3})

The library (as the PHP and ones). Uses a builder class to create our instances

from queue import Queue
from rpc import RPC
from exchange import Exchange

defaults = {
    'queue': {
        'queue': {
            'passive': False,
            'durable': True,
            'exclusive': False,
            'autoDelete': False,
            'nowait': False
        },
        'consumer': {
            'noLocal': False,
            'noAck': False,
            'exclusive': False,
            'nowait': False
        }
    },
    'exchange': {
        'exchange': {
            'passive': False,
            'durable': True,
            'autoDelete': True,
            'internal': False,
            'nowait': False
        },
        'queue': {
            'passive': False,
            'durable': True,
            'exclusive': False,
            'autoDelete': True,
            'nowait': False
        },
        'consumer': {
            'noLocal': False,
            'noAck': False,
            'exclusive': False,
            'nowait': False
        }
    },
    'rpc': {
        'queue': {
            'passive': False,
            'durable': True,
            'exclusive': False,
            'autoDelete': True,
            'nowait': False
        },
        'consumer': {
            'noLocal': False,
            'noAck': False,
            'exclusive': False,
            'nowait': False
        }
    }
}

def queue(name, server):
    conf = defaults['queue']
    conf['server'] = server

    return Queue(name, conf)

def rpc(name, server):
    conf = defaults['rpc']
    conf['server'] = server

    return RPC(name, conf)

def exchange(name, server):
    conf = defaults['exchange']
    conf['server'] = server

    return Exchange(name, conf)

And our Queue class

import pika
import json
import time

class Queue:
    def __init__(self, name, conf):
        self.name = name
        self.conf = conf

    def emit(self, data=None):
        credentials = pika.PlainCredentials(self.conf['server']['user'], self.conf['server']['pass'])
        connection = pika.BlockingConnection(pika.ConnectionParameters(host=self.conf['server']['host'], port=self.conf['server']['port'], credentials=credentials))
        channel = connection.channel()

        queueConf = self.conf['queue']
        channel.queue_declare(queue=self.name, passive=queueConf['passive'], durable=queueConf['durable'], exclusive=queueConf['exclusive'], auto_delete=queueConf['autoDelete'])

        channel.basic_publish(exchange='', routing_key=self.name, body=json.dumps(data), properties=pika.BasicProperties(delivery_mode=2))
        connection.close()

    def receive(self, callback):
        credentials = pika.PlainCredentials(self.conf['server']['user'], self.conf['server']['pass'])
        connection = pika.BlockingConnection(pika.ConnectionParameters(host=self.conf['server']['host'], port=self.conf['server']['port'], credentials=credentials))
        channel = connection.channel()

        queueConf = self.conf['queue']
        channel.queue_declare(queue=self.name, passive=queueConf['passive'], durable=queueConf['durable'], exclusive=queueConf['exclusive'], auto_delete=queueConf['autoDelete'])

        def _callback(ch, method, properties, body):
            callback(json.loads(body))
            ch.basic_ack(delivery_tag=method.delivery_tag)
            print "%s %s::%s" % (time.strftime("[%d/%m/%Y-%H:%M:%S]", time.localtime(time.time())), self.name, body)

        print "%s Queue '%s' initialized" % (time.strftime("[%d/%m/%Y-%H:%M:%S]", time.localtime(time.time())), self.name)
        consumerConf = self.conf['consumer']
        channel.basic_qos(prefetch_count=1)
        channel.basic_consume(_callback, self.name, no_ack=consumerConf['noAck'], exclusive=consumerConf['exclusive'])

        channel.start_consuming()

We also want to use exchanges to emit messages without waiting for answers, just as a event broadcast. We can emit messages:

from rabbit import builder

server = {
    'host': 'localhost',
    'port': 5672,
    'user': 'guest',
    'pass': 'guest',
}

exchange = builder.exchange('process.log', server)

exchange.emit("xxx.log", "aaaa")
exchange.emit("xxx.log", ["11", "aaaa"])
exchange.emit("yyy.log", "aaaa")

And listen to messages

from rabbit import builder

server = {
    'host': 'localhost',
    'port': 5672,
    'user': 'guest',
    'pass': 'guest',
}

def onData(routingKey, data):
    print routingKey, data

builder.exchange('process.log', server).receive("yyy.log", onData)

That’s the class

import pika
import json
import time

class Exchange:
    def __init__(self, name, conf):
        self.name = name
        self.conf = conf

    def emit(self, routingKey, data=None):
        credentials = pika.PlainCredentials(self.conf['server']['user'], self.conf['server']['pass'])
        connection = pika.BlockingConnection(pika.ConnectionParameters(host=self.conf['server']['host'], port=self.conf['server']['port'], credentials=credentials))
        channel = connection.channel()

        exchangeConf = self.conf['exchange']
        channel.exchange_declare(exchange=self.name, type='topic', passive=exchangeConf['passive'], durable=exchangeConf['durable'], auto_delete=exchangeConf['autoDelete'], internal=exchangeConf['internal'])
        channel.basic_publish(exchange=self.name, routing_key=routingKey, body=json.dumps(data))
        connection.close()

    def receive(self, bindingKey, callback):
        credentials = pika.PlainCredentials(self.conf['server']['user'], self.conf['server']['pass'])
        connection = pika.BlockingConnection(pika.ConnectionParameters(host=self.conf['server']['host'], port=self.conf['server']['port'], credentials=credentials))
        channel = connection.channel()

        exchangeConf = self.conf['exchange']
        channel.exchange_declare(exchange=self.name, type='topic', passive=exchangeConf['passive'], durable=exchangeConf['durable'], auto_delete=exchangeConf['autoDelete'], internal=exchangeConf['internal'])

        queueConf = self.conf['queue']
        result = channel.queue_declare(passive=queueConf['passive'], durable=queueConf['durable'], exclusive=queueConf['exclusive'], auto_delete=queueConf['autoDelete'])
        queue_name = result.method.queue

        channel.queue_bind(exchange=self.name, queue=queue_name, routing_key=bindingKey)

        print "%s Exchange '%s' initialized" % (time.strftime("[%d/%m/%Y-%H:%M:%S]", time.localtime(time.time())), self.name)

        def _callback(ch, method, properties, body):
            callback(method.routing_key, json.loads(body))
            ch.basic_ack(delivery_tag=method.delivery_tag)
            print "%s %s:::%s" % (time.strftime("[%d/%m/%Y-%H:%M:%S]", time.localtime(time.time())), self.name, body)

        consumerConf = self.conf['consumer']
        channel.basic_consume(_callback, queue=queue_name, no_ack=consumerConf['noAck'], exclusive=consumerConf['exclusive'])
        channel.start_consuming()

And finally we can use RPCs. Emit

from rabbit import builder

server = {
    'host': 'localhost',
    'port': 5672,
    'user': 'guest',
    'pass': 'guest',
}

print builder.rpc('rpc.hello', server).call("Gonzalo", "Ayuso")

And the server side

from rabbit import builder

server = {
    'host': 'localhost',
    'port': 5672,
    'user': 'guest',
    'pass': 'guest',
}

def onData(name, surname):
    return "Hello %s %s" % (name, surname)

builder.rpc('rpc.hello', server).server(onData)

And that’s the class

import pika
import json
import time
import uuid

class RPC:
    def __init__(self, name, conf):
        self.name = name
        self.conf = conf

    def call(self, *params):
        pika.PlainCredentials(self.conf['server']['user'], self.conf['server']['pass'])
        connection = pika.BlockingConnection(pika.ConnectionParameters(host=self.conf['server']['host'], port=self.conf['server']['port']))
        channel = connection.channel()

        queueConf = self.conf['queue']
        result = channel.queue_declare(queue='', passive=queueConf['passive'], durable=queueConf['durable'], exclusive=queueConf['exclusive'], auto_delete=queueConf['autoDelete'])
        callback_queue = result.method.queue
        consumerConf = self.conf['consumer']
        channel.basic_consume(self.on_call_response, no_ack=consumerConf['noAck'], exclusive=consumerConf['exclusive'], queue='')

        self.response = None
        self.corr_id = str(uuid.uuid4())
        channel.basic_publish(exchange='', routing_key=self.name, properties=pika.BasicProperties(reply_to=callback_queue, correlation_id=self.corr_id), body=json.dumps(params))
        while self.response is None:
            connection.process_data_events()
        return self.response

    def on_call_response(self, ch, method, props, body):
        if self.corr_id == props.correlation_id:
            self.response = body

    def server(self, callback):
        pika.PlainCredentials(self.conf['server']['user'], self.conf['server']['pass'])
        connection = pika.BlockingConnection(pika.ConnectionParameters(host=self.conf['server']['host'], port=self.conf['server']['port']))
        channel = connection.channel()

        queueConf = self.conf['queue']
        channel.queue_declare(self.name, passive=queueConf['passive'], durable=queueConf['durable'], exclusive=queueConf['exclusive'], auto_delete=queueConf['autoDelete'])

        channel.basic_qos(prefetch_count=1)
        consumerConf = self.conf['consumer']

        def on_server_request(ch, method, props, body):
            response = callback(*json.loads(body))

            ch.basic_publish(exchange='', routing_key=props.reply_to, properties=pika.BasicProperties(correlation_id=props.correlation_id), body=json.dumps(response))
            ch.basic_ack(delivery_tag=method.delivery_tag)
            print "%s %s::req => '%s' response => '%s'" % (time.strftime("[%d/%m/%Y-%H:%M:%S]", time.localtime(time.time())), self.name, body, response)

        channel.basic_consume(on_server_request, queue=self.name, no_ack=consumerConf['noAck'], exclusive=consumerConf['exclusive'])

        print "%s RPC '%s' initialized" % (time.strftime("[%d/%m/%Y-%H:%M:%S]", time.localtime(time.time())), self.name)
        channel.start_consuming()

And that’s all. Full project is available within my github account

Playing with Docker, Silex, Python, Node and WebSockets

I’m learning Docker. In this post I want to share a little experiment that I have done. I know the code looks like over-engineering but it’s just an excuse to build something with docker and containers. Let me explain it a little bit.

The idea is build a Time clock in the browser. Something like this:

Clock

Yes I know. We can do it only with js, css and html but we want to hack a little bit more. The idea is to create:

  • A Silex/PHP frontend
  • A WebSocket server with socket.io/node
  • A Python script to obtain the current time

WebSocket server will open 2 ports: One port to serve webSockets (socket.io) and another one as a http server (express). Python script will get the current time and it’ll send it to the webSocket server. Finally one frontend(silex) will be listening to WebSocket’s event and it will render the current time.

That’s the WebSocket server (with socket.io and express)

var
    express = require('express'),
    expressApp = express(),
    server = require('http').Server(expressApp),
    io = require('socket.io')(server, {origins: 'localhost:*'})
    ;

expressApp.get('/tic', function (req, res) {
    io.sockets.emit('time', req.query.time);
    res.json('OK');
});

expressApp.listen(6400, '0.0.0.0');

server.listen(8080);

That’s our Python script

from time import gmtime, strftime, sleep
import httplib2

h = httplib2.Http()
while True:
    (resp, content) = h.request("http://node:6400/tic?time=" + strftime("%H:%M:%S", gmtime()))
    sleep(1)

And our Silex frontend

use Silex\Application;
use Silex\Provider\TwigServiceProvider;

$app = new Application(['debug' => true]);
$app->register(new TwigServiceProvider(), [
    'twig.path' => __DIR__ . '/../views',
]);

$app->get("/", function (Application $app) {
    return $app['twig']->render('index.twig', []);
});

$app->run();

using this twig template

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Docker example</title>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
    <link href="css/app.css" rel="stylesheet">
    <script src="https://oss.maxcdn.com/html5shiv/3.7.3/html5shiv.min.js"></script>
    <script src="https://oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
</head>
<body>
<div class="site-wrapper">
    <div class="site-wrapper-inner">
        <div class="cover-container">
            <div class="inner cover">
                <h1 class="cover-heading">
                    <div id="display">
                        display
                    </div>
                </h1>
            </div>
        </div>
    </div>
</div>
<script src="//localhost:8080/socket.io/socket.io.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
var socket = io.connect('//localhost:8080');

$(function () {
    socket.on('time', function (data) {
        $('#display').html(data);
    });
});
</script>
</body>
</html>

The idea is to use one Docker container for each process. I like to have all the code in one place so all containers will share the same volume with source code.

First the node container (WebSocket server)

FROM node:argon

RUN mkdir -p /mnt/src
WORKDIR /mnt/src/node

EXPOSE 8080 6400

Now the python container

FROM python:2

RUN pip install httplib2

RUN mkdir -p /mnt/src
WORKDIR /mnt/src/python

And finally Frontend contailer (apache2 with Ubuntu 16.04)

FROM ubuntu:16.04

RUN locale-gen es_ES.UTF-8
RUN update-locale LANG=es_ES.UTF-8
ENV DEBIAN_FRONTEND=noninteractive

RUN apt-get update -y
RUN apt-get install --no-install-recommends -y apache2 php libapache2-mod-php
RUN apt-get clean -y

COPY ./apache2/sites-available/000-default.conf /etc/apache2/sites-available/000-default.conf

RUN mkdir -p /mnt/src

RUN a2enmod rewrite
RUN a2enmod proxy
RUN a2enmod mpm_prefork

RUN chown -R www-data:www-data /mnt/src
ENV APACHE_RUN_USER www-data
ENV APACHE_RUN_GROUP www-data
ENV APACHE_LOG_DIR /var/log/apache2
ENV APACHE_LOCK_DIR /var/lock/apache2
ENV APACHE_PID_FILE /var/run/apache2/apache2.pid
ENV APACHE_SERVERADMIN admin@localhost
ENV APACHE_SERVERNAME localhost

EXPOSE 80

Now we’ve got the three containers but we want to use all together. We’ll use a docker-compose.yml file. The web container will expose port 80 and node container 8080. Node container also opens 6400 but this port is an internal port. We don’t need to access to this port outside. Only Python container needs to access to this port. Because of that 6400 is not mapped to any port in docker-compose

version: '2'

services:
  web:
    image: gonzalo123/example_web
    container_name: example_web
    ports:
     - "80:80"
    restart: always
    depends_on:
      - node
    build:
      context: ./images/php
      dockerfile: Dockerfile
    entrypoint:
      - /usr/sbin/apache2
      - -D
      - FOREGROUND
    volumes:
     - ./src:/mnt/src

  node:
    image: gonzalo123/example_node
    container_name: example_node
    ports:
     - "8080:8080"
    restart: always
    build:
      context: ./images/node
      dockerfile: Dockerfile
    entrypoint:
      - npm
      - start
    volumes:
     - ./src:/mnt/src

  python:
      image: gonzalo123/example_python
      container_name: example_python
      restart: always
      depends_on:
        - node
      build:
        context: ./images/python
        dockerfile: Dockerfile
      entrypoint:
        - python
        - tic.py
      volumes:
       - ./src:/mnt/src

And that’s all. We only need to start our containers

docker-compose up --build -d

and open our browser at: http://localhost to see our Time clock

Full source code available within my github account

Playing with arduino, IoT, crossbar and websockets

Yes. Finally I’ve got an arduino board. It’s time to hack a little bit. Today I want to try different things. I want to display in a webpage one value from my arduino board. For example one analog data using a potentiometer. Let’s start.

We are going to use one potentiometer. A potentiometer is a resistor with a rotating contact that forms an adjustable voltage divider. It has three pins. If we connect one pin to 5V power source of our arduino, another one to the ground and another to one A0 (analog input 0), we can read different values depending on the position of potentiometer’s rotating contact.

arduino_analog

Arduino has 10 bit analog resolution. That means 1024 possible values, from 0 to 1023. So when our potentiometer gives us 5 volts we’ll obtain 1024 and when our it gives us 0V we’ll read 0. Here we can see a simple arduino program to read this analog input and send data via serial port:

int mem;

void setup() {
  Serial.begin(9600);
}

void loop() {
  int value = analogRead(A0);
  if (value != mem) {
    Serial.println(value);
  }
  mem = value;

  delay(100);
}

This program is simple loop with a delay of 100 milliseconds that reads A0 and if value is different than previously read (to avoid sending the same value when nobody is touching the potentiometer) we send the value via serial port (with 9600 bauds)

We can test our program using the serial monitor of our arduino IDE our using another serial monitor.

Now we’re going to create one script to read this serial port data. We’re going to use Python. I’ll use my laptop and my serial port is /dev/tty.usbmodem14231

import serial

arduino = serial.Serial('/dev/tty.usbmodem14231', 9600)

while 1:
  print arduino.readline().strip()

Basically we’ve got our backend running. Now we can create a simple frontend.

...
<div id='display'></div>
...

We’ll need websockets. I normally use socket.io but today I’ll use Crossbar.io. Since I hear about it in a Ronny’s talk at deSymfony conference I wanted to use it.

I’ll change a little bit our backend to emit one event

import serial
from os import environ
from twisted.internet.defer import inlineCallbacks
from twisted.internet.task import LoopingCall
from autobahn.twisted.wamp import ApplicationSession, ApplicationRunner

arduino = serial.Serial('/dev/tty.usbmodem14231', 9600)

class SeriaReader(ApplicationSession):
    @inlineCallbacks
    def onJoin(self, details):
        def publish():
            return self.publish(u'iot.serial.reader', arduino.readline().strip())

        yield LoopingCall(publish).start(0.1)

if __name__ == '__main__':
    runner = ApplicationRunner(environ.get("GONZALO_ROUTER", u"ws://127.0.0.1:8080/ws"), u"iot")
    runner.run(SeriaReader)

Now I only need to create a crossbar.io server. I will use node to do it

var autobahn = require('autobahn'),
    connection = new autobahn.Connection({
            url: 'ws://0.0.0.0:8080/ws',
            realm: 'iot'
        }
    );

connection.open();

And now we only need to connect our frontend to the websocket server

$(function () {
    var connection = new autobahn.Connection({
        url: "ws://192.168.1.104:8080/ws",
        realm: "iot"
    });

    connection.onopen = function (session) {
        session.subscribe('iot.serial.reader', function (args) {
            $('#display').html(args[0]);
        });
    };

    connection.open();
});

It works but thre’s a problem. The first time we connect with our browser we won’t see the display value until we change the position of the potentiometer. That’s because ‘iot.serial.reader’ event is only emitted when potentiometer changes. No change means no new value. To solve this problem we only need to change a little bit our crossbar.io server. We’ll “memorize” the last value and we’ll expose one method ‘iot.serial.get’ to ask about this value

var autobahn = require('autobahn'),
    connection = new autobahn.Connection({
            url: 'ws://0.0.0.0:8080/ws',
            realm: 'iot'
        }
    ),
    mem;

connection.onopen = function (session) {
    session.register('iot.serial.get', function () {
        return mem;
    });

    session.subscribe('iot.serial.reader', function (args) {
        mem = args[0];
    });
};

connection.open();

An now in the frontend we ask for ‘iot.serial.get’ when we connect to the socket

$(function () {
    var connection = new autobahn.Connection({
        url: "ws://192.168.1.104:8080/ws",
        realm: "iot"
    });

    connection.onopen = function (session) {
        session.subscribe('iot.serial.reader', function (args) {
            $('#display').html(args[0]);
        }).then(function () {
                session.call('iot.serial.get').then(
                    function (result) {
                        $('#display').htmlresult);
                    }
                );
            }
        );
    };
    connection.open();
});

And thats all. The source code is available in my github account. You also can see a demo of the working prototype here

Smart bulb controlled from a Raspberry Pi with Python. My RGB alarm clock

I’ve got a BeeWi Smart LED Color Bulb. I must admit I cannot resist to buy those kind of devices :).

I can switch on/off the bulb and change the color using its Mobile App, but it’s not fun. I want to play a little bit with the bulb. My idea is the following one: First switch on the bulb in the mornint and set up the bulb color (Blue for example). Then change bulb color depending on my morning routine. And finally switch the bulb off. Now with this bulb’s color I know if my morning routine is on-time, just looking at the bulb’s color. For example if the bulb is red and I’m still having breakfast probably I’m late.

The prototype is very simple. The bulb has a bluetooth interface and I’ve found a python script to control the bulb. I’ve changed a little bit this script to adapt it to my needs.

Now I only need to set up the crontab within my Raspberry Pi to trigger the script and switch on/off the bulb and change the RGB color.

for example:

# switch on the bulb
/usr/bin/python /mnt/media/projects/iot/bulb.py /mnt/media/projects/iot/conf.json on
# set bulb's color to green
/usr/bin/python /mnt/media/projects/iot/bulb.py /mnt/media/projects/iot/conf.json colour 999900

In another post we play with Telegram bots to read temperature. Now I’ve adapted also my bot to switch on/off and change color of the bulb.

Now I’ve got another toy in my desk. One arduino board. I’m sure I will enjoy a lot 🙂

Home automation pet project. Playing with IoT, temperature sensors, fans and Telegram bots

Summer holidays are over. Besides my bush walks I’ve been also hacking a little bit with one idea that I had in mind. Summer means high temperatures and I wanted to control my fan. For example turn on the fan when temperature is over a threshold. I can do it using an Arduino board and a temperature sensor, but I don’t have the one Arduino board. I have several devices. For example a Wemo switch. With this device connected to my Wifi network I can switch on and off my fan remotely from my mobile phone (using its android app) or even from my Pebble watch using the API. I also have a BeeWi temperature/humidity sensor. It’s a BTLE device. It comes with its own app for android, but there’s also a API. Yes. I known that one Arduino board with a couple of sensors can be cheaper than one of this devices, but when I’m a shop and I’ve got one of this devices in my hands I cannot resist.

I also have a new Raspberry pi 3. I’ve recently upgraded my home multimedia server from a rpi2 to the new rpi3. Basically I use it as multimedia server and now also as retro console. This new rpi3 has Bluetooth so I wanted to do something with it. Read temperature from the Bluetooth sensor sounds good so I started to hack a little bit.

I found this post. I started working with Python. The script almost works but it uses Bluetooth connection and as someone said in the comments it uses a lot of battery. So I switched to a BTLE version. I found a simple node library to connect BTLE devices called noble, really simple to use. In one afternoon I had one small script ready. The idea was put this script in my RP3’s crontab, and scan the temperature each minute (via noble) and if the temperature was over a threshold switch on the wemo device (via ouimeaux). I also wanted to be informed when my fan is switch on and off. The most easier way to do it was via Telegram (I already knew telebot library).

var noble = require('noble'),
    Wemo = require('wemo-client'),
    TeleBot = require('telebot'),
    fs = require('fs'),
    beeWiData,
    wemo,
    threshold,
    address,
    bot,
    chatId,
    wemoDevice,
    configuration,
    confPath;

if (process.argv.length <= 2) {
    console.log("Usage: " + __filename + " conf.json");
    process.exit(-1);
}

confPath = process.argv[2];
try {
    configuration = JSON.parse(
        fs.readFileSync(process.argv[2])
    );
} catch (e) {
    console.log("configuration file not valid");
    process.exit(-1);
}

bot = new TeleBot(configuration.telegramBotAPIKey);
address = configuration.beeWiAddress;
threshold = configuration.threshold;
wemoDevice = configuration.wemoDevice;
chatId = configuration.telegramChatId;

function persists() {
    configuration.beeWiData = beeWiData;
    fs.writeFileSync(confPath, JSON.stringify(configuration));
}

function setSwitchState(state, callback) {
    wemo = new Wemo();
    wemo.discover(function(deviceInfo) {
        if (deviceInfo.friendlyName == wemoDevice) {
            console.log("device found:", deviceInfo.friendlyName, "setting the state to", state);
            var client = wemo.client(deviceInfo);
            client.on('binaryState', function(value) {
                callback();
            });

            client.on('statusChange', function(a) {
                console.log("statusChange", a);
            });
            client.setBinaryState(state);
        }
    });
}

beeWiData = {temperature: undefined, humidity: undefined, batery: undefined};

function hexToInt(hex) {
    if (hex.length % 2 !== 0) {
        hex = "0" + hex;
    }
    var num = parseInt(hex, 16);
    var maxVal = Math.pow(2, hex.length / 2 * 8);
    if (num > maxVal / 2 - 1) {
        num = num - maxVal;
    }
    return num;
}

noble.on('stateChange', function(state) {
    if (state === 'poweredOn') {
        noble.stopScanning();
        noble.startScanning();
    } else {
        noble.stopScanning();
    }
});

noble.on('scanStop', function() {
    var message, state;
    if (beeWiData.temperature > threshold) {
        state = 1;
        message = "temperature (" + beeWiData.temperature + ") over threshold (" + threshold + "). Fan ON. Humidity: " + beeWiData.humidity;
    } else {
        message = "temperature (" + beeWiData.temperature + ") under threshold (" + threshold + "). Fan OFF. Humidity: " + beeWiData.humidity;
        state = 0;
    }
    setSwitchState(state, function() {
        if (configuration.beeWiData.hasOwnProperty('temperature') && configuration.beeWiData.temperature < threshold && state === 1 || configuration.beeWiData.temperature > threshold && state === 0) {
            console.log("Notify to telegram bot", message);
            bot.sendMessage(chatId, message).then(function() {
                process.exit(0);
            }, function(e) {
                console.error(e);
                process.exit(0);
            });
            persists();
        } else {
            console.log(message);
            persists();
            process.exit(0);
        }
    });
});

noble.on('discover', function(peripheral) {
    if (peripheral.address == address) {
        var data = peripheral.advertisement.manufacturerData.toString('hex');
        beeWiData.temperature = parseFloat(hexToInt(data.substr(10, 2)+data.substr(8, 2))/10).toFixed(1);
        beeWiData.humidity = Math.min(100,parseInt(data.substr(14, 2),16));
        beeWiData.batery = parseInt(data.substr(24, 2),16);
        beeWiData.date = new Date();
        noble.stopScanning();
    }
});

setTimeout(function() {
    console.error("timeout exceded!");
    process.exit(0);
}, 5000);

The script is here.

It works but I wanted to keep on hacking. One Sunday morning I read this post. I don’t have an amazon button, but I wanted to do something similar. I started to play with scapy library sniffing ARP packets in my home network. I realize that I can detect when my Kindle connects to the network, my tv, or even my mobile phone. Then I had one I idea: Detect when my mobile phone connects to my wifi. My mobile phone connects to my wifi before I enter in my house so my idea was simple: Detect when I’m close to my home’s door and send me a telegram message saying “Wellcome home” in addition to the temperature inside my house at this moment.

#!/usr/bin/env python

import sys
from scapy.all import *
import telebot
import gearman
import json
from StringIO import StringIO

BUFFER_SIZE = 1024

try:
    with open(sys.argv[1]) as data_file:
        data = json.load(data_file)
        myPhone = data['myPhone']
        routerIP = data['routerIP']
        TOKEN = data['telegramBotAPIKey']
        chatID = data['telegramChatId']
        gearmanServer = data['gearmanServer']
except:
    print("Unexpected error:", sys.exc_info()[0])
    raise

def getSensorData():
    gm_client = gearman.GearmanClient([gearmanServer])
    completed_job_request = gm_client.submit_job("temp", '')
    io = StringIO(completed_job_request.result)

    return json.load(io)

tb = telebot.TeleBot(TOKEN)

def arp_display(pkt):
    if pkt[ARP].op == 1 and pkt[ARP].hwsrc == myPhone and pkt[ARP].pdst == routerIP:
        sensorData = getSensorData()
        message = "Wellcome home Gonzalo! Temperature: %s humidity: %s" % (sensorData['temperature'], sensorData['humidity'])
        tb.send_message(chatID, message)
        print message

print sniff(prn=arp_display, filter='arp', store=0)

I have one node script to read temperature and one Python script to sniff my network. I can find how to read temperature from Python and use only one script but I was lazy (remember that I was on holiday) so I turned the node script that reads temperature into a gearman worker.

var noble = require('noble'),
    fs = require('fs'),
    Gearman = require('node-gearman'),
    beeWiData,
    address,
    bot,
    configuration,
    confPath,
    status,
    callback;

var gearman = new Gearman();

if (process.argv.length <= 2) {
    console.log("Usage: " + __filename + " conf.json");
    process.exit(-1);
}

confPath = process.argv[2];
try {
    configuration = JSON.parse(
        fs.readFileSync(process.argv[2])
    );
} catch (e) {
    console.log("configuration file not valid", e);
    process.exit(-1);
}

address = configuration.beeWiAddress;
delay = configuration.tempServerDelayMinutes * 60 * 1000;
tcpPort = configuration.tempServerPort;

beeWiData = {};

function hexToInt(hex) {
    if (hex.length % 2 !== 0) {
        hex = "0" + hex;
    }
    var num = parseInt(hex, 16);
    var maxVal = Math.pow(2, hex.length / 2 * 8);
    if (num > maxVal / 2 - 1) {
        num = num - maxVal;
    }
    return num;
}

noble.on('stateChange', function(state) {
    if (state === 'poweredOn') {
        console.log("stateChange:poweredOn");
        status = true;
    } else {
        status = false;
    }
});

noble.on('discover', function(peripheral) {
    if (peripheral.address == address) {
        var data = peripheral.advertisement.manufacturerData.toString('hex');
        beeWiData.temperature = parseFloat(hexToInt(data.substr(10, 2)+data.substr(8, 2))/10).toFixed(1);
        beeWiData.humidity = Math.min(100,parseInt(data.substr(14, 2),16));
        beeWiData.batery = parseInt(data.substr(24, 2),16);
        beeWiData.date = new Date();
        noble.stopScanning();
    }
});

noble.on('scanStop', function() {
    console.log(beeWiData);
    noble.stopScanning();
    callback();
});

var worker;

function workerCallback(payload, worker) {
    callback = function() {
        worker.end(JSON.stringify(beeWiData));
    }

    beeWiData = {temperature: undefined, humidity: undefined, batery: undefined};

    if (status) {
        noble.stopScanning();
        noble.startScanning();
    } else {
        setInterval(function() {
            workerCallback(payload, worker);
        }, 1000);
    }
}

gearman.registerWorker("temp", workerCallback);

Now I only need to call this worker from my Python sniffer and thats all.

I wanted to play a little bit. I also wanted to ask the temperature on demand. Since I was using Telegram I had an idea. Create a Telegram bot running in my RP3. And that’s my summer pet project. Basically it has three parts:

worker.js
It’s a gearman worker. It reads temperature and humidity from my BeeWi sensor via BTLE

bot.py
It’s a Telegram bot with the following commands available:

/switchInfo: get switch info
/switchOFF: switch OFF the switch
/help: Gives you information about the available commands
/temp: Get temperature
/switchON: switch ON the switch

sniff.py
It’s just a ARP sniffer. It detects when I’m close to my home and sends me a message via Telegram with the temperature. It detects when my mobile phone sends a ARP package to my router (aka when I connect to my Wifi). It happens before I enter in my house, so the Telegram message arrives before I put the key in the door 🙂

I run al my scripts in my Raspberry Pi3. To ensure all scripts are up an running I use supervisor

All the scripts are available in my github account

Reading Modbus devices with Python from a PHP/Silex Application via Gearman worker

Yes. I know. I never know how to write a good tittle to my posts. Let me show one integration example that I’ve been working with this days. Let’s start.

In industrial automation there’re several standard protocols. Modbus is one of them. Maybe isn’t the coolest or the newest one (like OPC or OPC/UA), but we can speak Modbus with a huge number of devices.

I need to read from one of them, and show a couple of variables in a Web frontend. Imagine the following fake Modbus server (it emulates my real Modbus device)

#!/usr/bin/env python

##
# Fake modbus server
# - exposes "Energy" 66706 = [1, 1170]
# - exposes "Power" 132242 = [2, 1170]
##

from pymodbus.datastore import ModbusSlaveContext, ModbusServerContext
from pymodbus.datastore import ModbusSequentialDataBlock
from pymodbus.server.async import StartTcpServer
import logging

logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

hrData = [1, 1170, 2, 1170]
store = ModbusSlaveContext(hr=ModbusSequentialDataBlock(2, hrData))

context = ModbusServerContext(slaves=store, single=True)

StartTcpServer(context)

This server exposes two variables “Energy” and “Power”. This is a fake server and it will returns always 66706 for energy and 132242 for power. Mobus is a binary protocol so 66706 = [1, 1170] and 132242 = [2, 1170]

I can read Modbus from PHP, but normally use Python for this kind of logic. I’m not going to re-write an existing logic to PHP. I’m not crazy enough. Furthermore my real Modbus device only accepts one active socket to retrieve information. That’s means if two clients uses the frontend at the same time, it will crash. In this situations Queues are our friends.

I’ll use a Gearman worker (written in Python) to read Modbus information.

from pyModbusTCP.client import ModbusClient
from gearman import GearmanWorker
import json

def reader(worker, job):
    c = ModbusClient(host="localhost", port=502)

    if not c.is_open() and not c.open():
        print("unable to connect to host")

    if c.is_open():

        holdingRegisters = c.read_holding_registers(1, 4)

        # Imagine we've "energy" value in position 1 with two words
        energy = (holdingRegisters[0] << 16) | holdingRegisters[1]

        # Imagine we've "power" value in position 3 with two words
        power = (holdingRegisters[2] << 16) | holdingRegisters[3]

        out = {"energy": energy, "power": power}
        return json.dumps(out)
    return None

worker = GearmanWorker(['127.0.0.1'])

worker.register_task('modbusReader', reader)

print 'working...'
worker.work()

Our backend is ready. Now we’ll work with the frontend. In this example I’ll use PHP and Silex.

<?php
include __DIR__ . '/../vendor/autoload.php';
use Silex\Application;
$app = new Application(['debug' => true]);
$app->register(new Silex\Provider\TwigServiceProvider(), array(
    'twig.path' => __DIR__.'/../views',
));
$app['modbusReader'] = $app->protect(function() {
    $client = new \GearmanClient();
    $client->addServer();
    $handle = $client->doNormal('modbusReader', 'modbusReader');
    $returnCode = $client->returnCode();
    if ($returnCode != \GEARMAN_SUCCESS) {
        throw new \Exception($this->client->error(), $returnCode);
    } else {
        return json_decode($handle, true);
    }
});
$app->get("/", function(Application $app) {
    return $app['twig']->render('home.twig', $app['modbusReader']());
});
$app->run();

As we can see the frontend is a simple Gearman client. It uses our Python worker to read information from Modbus and render a simple html with a Twig template

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Demo</title>
</head>
<body>
    Energy: {{ energy }}
    Power: {{ power }}
</body>
</html>

And that’s all. You can see the full example in my github account

Building one HTTP client in PostgreSQL with PL/Python

Don’t ask me way, but I need to call to a HTTP server (one Silex application) from a PostgreSQL database.

I want to do something like this:

select get('http://localhost:8080?name=Gonzalo')->'hello';

PostgreSQL has a datatype for json. It’s really cool and it allows us to connect our HTTP server and our SQL database using same datatype.

PostgreSQL also allows us to create stored procedures using different languages. The default language is PL/pgSQL. PL/pgSQL is a simple language where we can embed SQL. But we also can use Python. With Python we can easily create HTTP clients, for example with urllib2. That means that develop our a HTTP client for a PostgreSQL database is pretty straightforward.

CREATE OR REPLACE FUNCTION get(uri character varying)
  RETURNS json AS
$BODY$
import urllib2

data = urllib2.urlopen(uri)

return data.read()

$BODY$
  LANGUAGE plpython2u VOLATILE
  COST 100;
ALTER FUNCTION get(character varying)
  OWNER TO gonzalo;

Ok that’s a GET client, but we also want a POST client to do something like this:

select post('http://localhost:8080', '{"name": "Gonzalo"}'::json)->'hello';

As you can see I want to use application/json instead of application/x-www-form-urlencoded to send request parameters. I wrote about it here time ago. So I will create one endpoint within my Silex server to handle my POST requests to:

<?php
include __DIR__ . '/../vendor/autoload.php';

use Silex\Application;
use Symfony\Component\HttpFoundation\Request;
use G\AngularPostRequestServiceProvider;

$app = new Application(['debug' => true]);

$app->register(new AngularPostRequestServiceProvider());

$app->post('/', function (Application $app, Request $request) {
    return $app->json(['hello' => $request->get('name')]);
});

$app->get('/', function (Application $app, Request $request) {
    return $app->json(['hello' => $request->get('name')]);
});

$app->run();

And now we only need to create one stored procedure to send POST requests

CREATE OR REPLACE FUNCTION post(
    uri character varying,
    paramenters json)
  RETURNS json AS
$BODY$
import urllib2

clen = len(paramenters)
req = urllib2.Request(uri, paramenters, {'Content-Type': 'application/json', 'Content-Length': clen})
f = urllib2.urlopen(req)
return f.read()

$BODY$
  LANGUAGE plpython2u VOLATILE
  COST 100;
ALTER FUNCTION post(character varying, json)
  OWNER TO gonzalo;

And that’s all. At least this simple script is exactly what I need.