Q:

MCP3008 analogue digital converter... how can I use it for the complete opposite of what it was made for?

I have set up an mcp3008 chip and a slide pot on my pi because I wanted a nice old fashioned volume control, and all of that seems to working fine and I am quite happy with it. 
Now I have 7 redundant analogue channels, which I would quite like to repurpose as simple on/off buttons, because the chip just happens to be there and it would save a bunch of gpio pins which I could use for more interesting stuff.
My problem is, they seem to float wildly all over the place when there is no voltage running through them, so while I can add a switch to one and read 3.3v reliably enough, when the switch is off they just read a bunch of noise. This doesn't happen with the slide pot, presumably since one end is grounded. 
Can anyone suggest a simple solution ? 
Shall I just live with the noise , or is there something really obvious I am missing?
Bear in mind I am asking because I am a complete moron as far as electronics are concerened, so no answer can be too patronising :)

A:

You will have to use a Pull-Up resistor to get clean difference between the two desired states.
This way you will have no floating input but either VCC (3.3V) or GND (0.0V) at the input of your MCP3008.
(You can ignore the logic gate in the image).
(Alternatively a Pull-Down resistor will work just as well).

