[Q] Writing a HTML/Javascript to control the car from a browser

[ghost]

Hi again,

Now that I have PI-RC working, is it possible to send UDP packets to the pi_pcm server from a web browser using Javascript? If so, what contents does the UDP packet contain exactly? Can you provide an example? Is it also possible for you to provide a simple Javascript that sends the packet?

I'm asking because I've written a web page for my current project which allows me to control a robot from my Nintendo 3DS and I think it would be awesome to create a page that works with Pi-RC too.

Thanks again!

[bskari]

That's a good idea, I like it! I'm pretty sure it's not possible to send UDP packets from JavaScript, but you should be able to send TCP packets using WebSockets. I have some time this weekend so I'll try to add TCP support to the server and add a sample page to the repository that you can use to send messages to the server to drive the var.

I have an example of what messages that you send should look like in the README. I think for your car, you'll want to do something similar to this (I've left out the web socket setup stuff though, I'll get a full example done this weekend. Also, I haven't tested any of this code.):

var forward = [
    // Synchronization burst
    {
        "frequency": 40.0,
        "dead_frequency": 26.995,
        "burst_us": 1200,
        "spacing_us": 400,
        "repeats": 4
    },
    // Command burst
    {
        "frequency": 40.0,
        "dead_frequency": 26.995,
        "burst_us": 400,
        "spacing_us": 400,
        "repeats": 11
    }
];
var message = JSON.stringify(forward);
socket.send(message);

[ghost]

Cool! Thanks!

[ghost]

Managed to create a PHP script that does it, fixed a issue with pi_pcm crashing after a few commands, too - it'd crash after receiving a specific .json command. Here's the script

<?php // Make car stop. $message = '[{ "frequency": 40.0, "dead_frequency": 26.995, "burst_us": 1200, "spacing_us": 400, "repeats": 4 } ]'; $server_ip = '127.0.0.1'; $server_port = 12345; if ($socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP)) { socket_sendto($socket, $message, strlen($message), 0, $server_ip, $server_port); } else { print("can't create socket\n"); }

?>

[bskari]

Okay, I added WebSocket support to the server. If you start it with ./pi_pcm --tcp, then you should be able to connect to the server by opening the control.html page with a browser (I tested Firefox and Chrome), entering in the control values or loading a JSON control file, and connecting to the server. Then just use the arrow keys.

There is a bug where occasionally the decoding of the message from the browser will fail and the server will ignore the message. I have no idea what's going on with that, but I'll try to fix it later. I'll leave this issue open in the mean time.

[ghost]

Oh wow! Thanks! I'll surely have fun with this nifty piece of html.