Automatically populating a text field using AJAX

Automatically populating a text field using AJAX

Hello,
 
I'm coming up to speed with JQM but am a newbie with AJAX.  What I'd like to do is dynamically populate a form's text field with data coming from a digital scale, refreshing every few seconds.  When the form gets submitted, the currently displayed weight gets inserted into the database via standard form processing.
 
The scales are on order and I've requested technical info, so I'll need to figure out some of the details when I have the hardware and specs.  We will be using PHP on the server side, perhaps the scales can send raw socket data or else output to a text file for processing...
 
Has anyone here done something like this before?
 
Thanks!
Kevin