Oscilloscope probe ...

[DeepCut]

Hi,

i've been using soundcard oscilloscope software to measure frequency.

I made two of the probes found here :

http://www.ladyada.net/library/equipt/d ... probe.html

They are fine for measureing frequency as my frequency output is low-voltage.

I'm developing an electric generator and need to see the waveforms in the output coils.

Can anyone advise me on how to modify the above probe design so that i can test coils that output a max of 200 volts ?

Would a simple voltage divider do the job ?

Any help greatly appreciated,


Cheers,

Gary.

[DeepCut]

OK i did it !

A simple voltage divider worked a treat, the AC sinewave is a bit dirty but it will do for now.

[hjohnson]

Yeeikes.... You're brave for letting ANYTHING with 200V get anywhere near your computer w/o isolation circuitry. I'm not sure what type of isolation they put in decent computer soundcards, but watch out. If it were me,I'd have put in some type of huge clamping diodes that prevent the voltage on the computer line from getting above a level that can be harmful. At least. But this seems to work for you, and god knows what sort of distortion those diodes could put on, so well done!

[DeepCut]

Hi HJ,

you're right, someone at another forum has given me a different circuit using some clipping diodes.

Also he says that my AC wave is dirty because my resistors (1M and 1K so 1001:1 ratio) make it too near ground level, he suggests a 200:1 ratio will give a cleaner result.

Also i am using an external USB sound module not a soundcard on the mainboard of the PC.

Someone also recommended one of these :

http://electronics-shop.dk/?id=1038&google=1


Cheers,

DC.

[hjohnson]

At that point, why don't you just get yourself an actual oscilloscope of ebay or craigslist for cheap? I bought mine for about $93, including shipping, (about 67 euros). Then you can get actual probes and/or make your own HV true probes (ala http://www.youtube.com/watch?v=jUvSP3BQpvs ) As long as you get one from a decent source, you can pick up a pretty decent 20MHz scope that has DC AND AC coupling (unlike soundcards that only have AC coupling, due to the internal DC blocking cap). For basic applications at low frequency and low voltage, the soundcard oscilloscope trick is great, but once you're looking to drop 34 euros on just making the thing safe, an actual scope looks much more appealing in my opinion.

[DeepCut]

Naaaa, mate - that would be too easy !

Seriously though, i'm gonna get myself one of these for xmas :

http://www.ebay.co.uk/itm/DSO5200-200MS ... 415d9db1ec

In the meantime it all helps me to learn (plus i'm impatient !).


Cheers,

Gary.