Question for electrical engineers

[Nowhere]

I have a toy project which involves using input of the soundcard as voltometer (it has that capability)...but the range of this input goes only to 2 V. Which will be enough for mine needs, however...what is the simple way of making sure that the voltage won't exceed few volts? (to avoid damaging the input of course).

Yes, putting proper resistor in there would work...but it would lower the sensitivity in the range I care about.

Or even...way to protect the device and some brilliant user if voltages will far exceed few volts, without adding much complexity to the design? (fuse would be ok I guess...but I'm also wondering if the circuit protecting against small voltage surge can be designed in a way to self-destruct in such case, without the need for fuse)

PS. Somehow "zener" rings in my head, but after checking it I'm not sure I can wrap my head around it
edit: or simply varistor?...

[Tjalfe]

A simple way is using a zener diode, which will break down at 2 volts( or pick one slightly less than 2 volts) that way any voltages above 2 volts will be shorted to ground. Connect between the input and the ground of the sound card. Cathode of the diode should be connected to the input, cathode to ground.
A fuse would only provide protection against too much current, not too high a voltage.

what sort of inputs are you measuring anyways?.. an op amp on the input could be used to scale the input voltage down in the allowed range.

[Nowhere]

What if "ground" isn't necesserilly available without remembering about connecting another cable to some grounded object?... (laptop)

Inputs - battery powered "experiments"...it's just that prefferably without making sure to use only AA ot AAA baterry.

[Tjalfe]

but you do have ground

[Nowhere]

Yeah that part I know

The things is...didn't realise that this works ok, even if you don't really have any proper grounding? (laptop after all...)

[Fat Tone]

Ground is just a term for the negative or return or - or lower potential or whatever word you prefer. A Zenner will prevent the voltage exceeding its breakdown voltage across the two points it is connected to.

An alternative for you might be one of the USB experimenters interface boards. I have one from Maplin that cost £25. http://www.maplin.co.uk/Search.aspx?...source=15&SD=Y But hey, I love your innovation

[rylan]

Oh and the Zener will act as a fuse if you put a high enough voltage on it, or overvolt a little with enough current.