User Guide for the PSLab Remote-Access Framework

The remote-lab framework of the pocket science lab has been designed to enable user to access their devices remotely via the internet. The pslab-remote repository includes an API server built with Python-Flask and a webapp that uses EmberJS. This post is a guide for users who wish to test the framework. A series of blog posts have been previously written which have explored and elaborated various aspect of the remote-lab such as designing the API server, remote execution of function strings, automatic deployment on various domains etc. In this post, we shall explore how to execute function strings, execute example scripts, and write a script ourselves.

A live demo is hosted at pslab-remote.surge.sh . The API server is hosted at pslab-stage.herokuapp.com, and an API reference which is being developed can be accessed at pslab-stage.herokuapp.com/apidocs . A screencast of the remote lab is also available

Create an account

Signing up at this point is very straightforward, and does not include any third party verification tools since the framework is under active development, and cannot be claimed to be ready for release yet.

Click on the sign-up button, and provide a username, email, and password. The e-mail will be used as the login-id, and needs to be unique.

Login to the remote lab

Use the email-id used for signing up, enter the password, and the app will redirect you to your new home-page, where you will be greeted with a similar screen.

Your home-page

On the home-page, you will find that the first section includes a text box for entering a function string, and an execute button. Here, you can enter any valid PSLab function such as `get_resistance()` , and click on the execute button in order to run the function on the PSLab device connected to the API server, and view the results. A detailed blog post on this process can be found here.

Since this is a new account, no saved scripts are present in the Your Scripts section. We will come to that shortly, but for now, there are some pre-written example scripts that will let you test them as well as view their source code in order to copy into your own collection, and modify them.

Click on the play icon next to `multimeter.py` in order to run the script. The eye icon to the right of the row enables you to view the source code, but this can also be done while the app is running. The multimeter app looks something like this, and you can click on the various buttons to try them out.

You may also click on the Source Code tab in order to view the source

Create and execute a small python script

We can now try to create a simple script of our own. Click on the `New Python Script` button in the top-bar to navigate to a page that will allow you to create and save your own scripts. We shall write a small 3-line code to print some sinusoidal coordinates, save it, and test it. Copy the following code for a sine wave with 30 points, and publish your script.

import numpy as np
x=np.linspace(0,2*np.pi,30)
print (x, np.sin(x))

Create a button widget and associate a callback to the get_voltage function

A small degree of object oriented capabilities have also been added, and the pslab-remote allows you to create button widgets and associate their targets with other widgets and labels.
The multimeter demo script uses this feature, and a single line of code suffices to demonstrate this feature.

button('Voltage on CH1 >',"get_voltage('CH1')","display_number")

You can copy the above line into a new script in order to try it out.

Associate a button’s callback to the capture routines, and set the target as a plot

The callback target for a button can be set to point to a plot. This is useful if the callback involves arrays such as those returned by the capture routines.

Example code to show a sine wave in a plot, and make button which will replace it with captured data from the oscilloscope:

import numpy as np
x=np.linspace(0,2*np.pi,30)
plt = plot(x, np.sin(x))
button('capture 1',"capture1('CH1',100,10)","update-plot",target=plt)
Figure: Demo animation from the plot_test example. Capture1 is connected to the plot shown.
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Designing a Remote Laboratory with PSLab using Python Flask Framework

In the introductory post about remote laboratories, a general set of tools to create a framework and handle its various aspects was also introduced. In this blog post, we will explore the implementation of several aspects of the backend app designed with python-flask, and the frontend based on EmberJS. A clear separation of the frontend and backend facilitates minimal disruption of either sections due to the other.

Implementing API methods in Python-Flask

In the Flask web server, page requests are handled via ‘routes’ , which are essentially URLs linked to a python function. Routes are also capable of handling payloads such as POST data, and various return types are also supported.

We shall use an example to demonstrate how a Sign-Up request sent from the sign-up form in the remote lab frontend for PSLab is handled.

@app.route('/signUp',methods=['POST'])
def signUp():
	"""Sign Up for Virtual Lab

	POST: Submit sign-up parameters. The following must be present:
	 inputName : The name of your account. does not need to be unique
	 inputEmail : e-mail ID used for login . must be unique.
	 inputPassword: password .
	Returns HTTP 404 when data does not exist.
	"""
	# read the posted values from the UI
	_name = request.form['inputName']
	_email = request.form['inputEmail']
	_password = request.form['inputPassword']

	# validate the received values
	if _name and _email and _password:
		_hashed_password = generate_password_hash(_password)
		newUser = User(_email, _name,_hashed_password)
		try:
			db.session.add(newUser)
			db.session.commit()
			return json.dumps({'status':True,'message':'User %s created successfully. e-mail:%s !'%(_name,_email)})
		except Exception as exc:
			reason = str(exc)
			return json.dumps({'status':False,'message':str(reason)})

 

In this example, the first line indicates that all URL requests made to <domain:port>/signUp will be handled by the function signUp . During development, we host the server on localhost, and use the default PORT number 8000, so sign-up forms must be submitted to 127.0.0.1:8000/signUp .

For deployment on a globally accessible server, a machine with a static IP, and a DNS record must be used. An example for such a deployment would be the heroku subdomain where pslab-remote is automatically deployed ; https://pslab-stage.herokuapp.com/signUp

A closer look at the above example will tell you that POST data can be accessed via the request.form dictionary, and that the sign-up routine requires inputName,inputEmail, and inputPassword. A password hash is generated before writing the parameters to the database.

Testing API methods using the Postman chrome extension

The route described in the above example requires form data to be submitted along with the URL, and we will use a rather handy developer tool called Postman to help us do this. In the frontend apps , AJAX methods are usually employed to do such tasks as well as handle the response from the server.

 

The above screenshot shows Postman being used to submit form data to /signUp on our API server running at localhost:8000 . The fields inputName, inputDescription, and inputPassword are also posted along with it.

In the bottom section, one can see that the server returned a positive status variable, as well as a descriptive message.

Submitting the sign up form via an Ember controller.
  • Setting up a template
    We first need to set up a template that we shall call sign-up.hbs , and add the following form to it. This form contains the details essential for signing up , and its submit action is linked to an action called `signMeUp` . This action will be defined in the controller which we shall explore shortly

<form class="form-signin" {{action "signMeUp" on="submit"}} >
        <label for="inputName" class="sr-only">Your Name</label>
        {{input value=inputName type="text" name="inputName" id="inputName" class="form-control" placeholder="name" required=true autofocus=true}}
        <label for="inputEmail" class="sr-only">Email address</label>
        {{input value=inputEmail type="email" name="inputEmail" id="inputEmail" class="form-control" placeholder="Email address" required=true autofocus=true}}
        <label for="inputPassword" class="sr-only">Password</label>
        {{input value=inputPassword type="password" name="inputPassword" id="inputPassword" class="form-control" placeholder="Password" required=true autofocus=true}}
         
        <button class="btn btn-lg btn-primary btn-block" type="submit">Sign Up</button>
</form>

 

  • Defining the controller
    The controller contains the actions and variables that the template links to. In this case, we require an action called signMeUp. The success, failure, and error handlers are hidden for clarity.

import Ember from 'ember';
export default Ember.Controller.extend({
  actions:{
    signMeUp() {
        var request = Ember.$.post("/signUp",
 this.getProperties("inputName","inputEmail","inputPassword"),this,'json');
        request.then(this.success.bind(this), this.failure.bind(this),
this.error.bind(this));
    },
  },
});

The signMeUp action submits the contents of the form to the signUp route on the API server, and the results are handled by functions called success, failure, or error depending on the type of response from the backend server.

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