Controll a C# application with a website accessed via smartphone

Hello tohether,
I am new in this forum. So sorry if I place a wrong question or use the wrong location.

In the last few weeks I have developed a small hardware device
which may be used for industrial automation.
In 2 weeks potential customers will come to my place and I nedd to prepare a demo.
To controll the device I have programmed a small C# application. (VS 2010 Express)

As far as I know the customres are crazy about smart phones.
So I am looking to enable the customer to remote controll by application
using his smart phone.

I do not want to programm a Android or Iphone application.
So I searched fpr different solutions.

The solution I am thinking of is to setup a wireless lan and to run a
webside on the industrial computer which can be accessed.
The user can hit a button on the website and this will change a parameter
in the C# application resulting in an response in my hardware device.

i never programmed a website. I even do not know which tools are needed.
I thought about using xampp and createing a website incliding java script.
And then to cretae a communication bettween C# and the website e.g. using java script.

I want to have 7 buttons and 7 textboxes on the website.
The text box displays a parameter like "low", "medium", "high".
If the customer hits the button he toggles from low to medium, medium to high or high to low
So the text in the textbox should change accordingly and the C# application
will set the hardware tothe same parameter.

Can anybody tell me if this is a good approach to enable my customer
to controll my application with his smartphone during the demo?
(it needs to run only at that day. never again, so the solution shoud be as
slim as possible)

If this is not a good idea I am happy to receive other suggestions.

If this is a good idea I am happy for any hint that makes my live easier.
Is there an better free tool then xampp?
Which free toll may I use to create the website?
How to comunicate best between the website and my application?
Is the sample source code or a sample project I may use?

Thanks in advance

Have a good day

Michael