PC-Soundcard-based oscilloscope ...

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Hi.

I am currently using a soundcard as a scope :

Hardware setup :

http://www.ladyada.net/library/equipt/diyaudioprobe.html

Software :

http://www.zeitnitz.de/Christian/scope_en

I will get a real scope but in the meantime i have a question.

I am trying to use my 'scope' to read the RPM of a magnetic-stator/rotor setup.

I am putting the 'probe' on a hookup wire that gets pulsed with a charge every time the reed-switch closes.

I was hoping that the frequency read-out from the scope (divided by the number of poles) would give me the RPM but it seems to fluctuate a fair bit and i know the RPM is not fluctuating that much.

Is this due to noisy PC electronics, does anyone have any experience with this poor-man's scope ?

Thanks.

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now i've blown the mic input on two soundcards, onward and upward ;+}

[pese]

i am workinking since years with tis.
you must not overload the input.
eventually limitimg with serie resistor or voltage divuder
gp

[DeepCut]

i am workinking since years with tis.
you must not overload the input.
eventually limitimg with serie resistor or voltage divuder
gp

Thanks pese. I am using a potentiometer and a 47mF cap but still blew the mic input, not sure why as i am new to electronics.

[pese]

Thanks pese. I am using a potentiometer and a 47mF cap but still blew the mic input, not sure why as i am new to electronics.

try to use an serie resistor 1meg  (100k) between pot (slider) and input to card.
be sure thas briund is also connected tocard (otherwise it is try to have problems)
Use shilded (like coax) cables from pot to the card-input
pese