Would a CRO as cheap as http://cgi.ebay.com.au/2-Channel-PC-Computer-Digital-Storage-USB-Oscilloscope-/400172785535?pt=AU_B_I_Electrical_Test_Equipment&hash=item5d2c281f7f do the job so long as the signal voltage <=5v? or are these really cheap ones not worth the box they come in?