I want to switch on/off the supply of power from a (movable) battery to the coil of a relay (movable with the battery) using a wireless (could be bluetooth) link from the USB port of a (fixed) PC.

Does any one know how this can be done using off the shelf componenst/software as I am not techy in this field?

 

Not withstanding the lack of any detail, why do you want to use the USB Interface?

It is adding huge complicatuon to a relativly simple task.

If you google RF remote kit you will find loads ...

That said I think this K8074 Velleman kit will do what you want out of the box.
It works with sevaral of their reciver boards including the smaller 1 and 2 channel ones.
Here is the link:-
http://www.velleman.eu/distributor/products/view/?id=370336

If you use a paralell port interface to control a transmitter programming will be much easer from almost any high level language.

You could perhaps buy a keyfob TX kit and replace the switches with a paralell port interface ...

By the way - Beware USB to paralell leads , most install as printers and not ports, you need a native LPT / ECP port if you go that way and control it programically.

Hope this all helps
Al

 

Are you trying to operate lighting or other appliances with your computer?

You can send a signal via USB to an RF transmitter.

The receiver can be attached to a relay and battery to activate the relay remotely.

Do a search on 'home automation'