A simple interface to mbed Device Connector, where you just declare variables to push them to the cloud.

Dependents:   Wifi_Get_Test_V1 simple-mbed-client-example simple-client-app-shield simple-sensor-client

Fork of simple-mbed-client by Jan Jongboom

TL;DR? See simple-mbed-client-example to get started immediately.

This library is a simpler interface to mbed Client, making it trivial to expose sensors, actuators and other variables to the cloud. It does not require you to change how you write your code. You can take any local variable, swap it out for a call to Simple Mbed Client, and the variable will automatically be synchronised with mbed Cloud.

For example, here's how you expose the value of a light sensor to the cloud:

SimpleMbedClient client;

SimpleResourceInt light_value = client.define_resource("light/0/value", 0);     // create the var

AnalogIn light(A1);

void read_light_sensor() {
    // light_value behaves just like a normal variable that you can read and write to!
    light_value = light.read_u16();

// update every second
Ticker t;
t.attach(&read_light_sensor, 1.0f);

Setting up

First import this library to your project. As Simple Mbed Client also needs a way to talk to the outside world, you'll need a NetworkInterface-object. The easiest way is by using the easy-connect library, so add that to your project as well. See the easy-connect docs on how to specify the connectivity method.

We also need a way of authenticating with mbed Cloud. For this we need a security certificate. Go to mbed Cloud, and select 'GET MY DEVICE SECURITY CREDENTIALS'. Save the certificate as security.h in your project folder.

Now we can initiate Simple Mbed Client and connect it to the internet.

#include "mbed.h"
#include "security.h"
#include "easy-connect.h"
#include "simple-mbed-client.h"

SimpleMbedClient client;

DigitalOut led(LED1, 0);

void registered() {
    led = 1;

int main() {
    NetworkInterface* network = connect_to_network(); // if connection failed, network will be NULL
    client.setup(network); // returns a bool, check if it's true


    while (1) {

Defining variables

You can define a new variable by a call to client.define_resource. This function takes five arguments:

  1. path - The URL on which your variable is exposed in mbed Cloud. Needs to be three (3) segments, split by a slash (/) in the form of 'sensor/0/value'. The second segment always needs to be numeric.
  2. defaultValue - The default value of the variable. Needs to be either a string or an integer. Depending on the type that you pass in here the type of the variable is defined.
  3. operation - Some variables might be read-only or write-only (seen from the cloud). Use the operation to define these constraints. It's of type M2MBase::Operation. Default is GET_PUT_ALLOWED.
  4. observable - If set to false, cloud applications cannot subscribe to updates on this variable. Default is true.
  5. callback - Function pointer which is called whenever the value of the variable is changed from the cloud.

The type returned by the function is either SimpleResourceInt or SimpleResourceString. You can assign and read from these variables like any normal local variable.

void name_updated(string new_value) {
    printf("Value is now %s\n", new_value.c_str());

SimpleResourceString name = client.define_resource("device/0/name", "jan", M2MBase::GET_PUT_ALLOWED, true, &name_updated);

// we can read and write to this variable, e.g.:
stringstream ss;
ss << name;

// or
name = "pietje";

// are all valid

Defining functions

You can define functions, which do not have a value, but can just be invoked from the cloud, by a call to client.define_function. This function takes two arguments:

  1. path - The URL on which your variable is exposed in mbed Cloud. Needs to be three (3) segments, split by a slash (/) in the form of 'sensor/0/value'. The second segment always needs to be numeric.
  2. callback - Function pointer which is invoked when the function is called. Takes in a pointer, which contains the data being passed in from the cloud.

void play(void* data) {
    if (data) { // data can be NULL!
        // cast it to something useful

client.define_function("music/0/play", &play);

Accessing the underlying M2MResource

If you need access to the underlying M2MResource you can do so by calling get_resource on a variable, or by calling client.get_resource if it's a function.

SimpleResourceInt led = client.define_resource("led/0/value", true);

client.define_function("led/0/toggle", &toggleLed);

// now to get the resource
M2MResource* ledResource = led.get_resource();
M2MResource* toggleResource = client.get_resource("led/0/toggle");

Printing variables

Unfortunately printf is kind of dumb, and does not automatically cast the variables. If you want to print any of the Simple Mbed Client variables you'll need to cast yourself.

SimpleResourceInt led = client.define_resource("led/0/value", true);

printf("Value is currently %d\n", static_cast<int>(led));

Event Queue

Simple Mbed Client uses an mbed-events EventQueue - running on a separate RTOS thread - to handle incoming events without blocking the main loop. Both the thread and event queue are created when initializing the library. You can override this behavior by providing your own event queue. In this case no thread is created.

EventQueue myQueue;
SimpleMbedClient client(&myQueue);

You can also use the queue to process your own events, which is very useful when dealing with ISRs. The queue is accessible through the eventQueue() function on the client object and returns a pointer to the queue.

SimpleMbedClient client;

InterruptIn btn(D2);

int main() {