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Author Message   Steve_s Tinkerer Username: Steve_s Post Number: 147 Registered: 07-2006 Rating: N/A Votes: 0 Posted on Monday, February 16, 2009 - 02:21 am:    If the input of your sound-card is very high impedance or ac coupled (i.e. through a capacitor) I don't think the first circuit can work because there will be little or no current through the transistor. I think the second circuit should work, but you may not need the capacitor. I use my own version http://www.ydo.abelgratis.co.uk/shutter_tester.html with Audacity and a Creative sound card.