I have just checked my laptop user manual and I have two inputs, microphone and line-input. Would it be possible to use an oscilloscope probe with say a 10x reduction. I did see a reference to a Virtins Sound Card Probe, but they appear to be in the States. Is there a UK version? What sort of plug fits the line-input? Is it a stereo plug like the microphone input?
The reason for my interest is that I am having a problem with using the pwm waveform to drive an h-bridge. My only piece of test equipment is a cheap digital dvm. The waveform is about 100Hz with a max amplitude of 5v. The simulated waveform from mplab looks fine. With no motor attached the average dc voltage, as measured by the dvm increases from about 0.7v to 4.5v, as I increase the speed control, but when I attach the motor to the bridge the average voltage only rises from 0.7 to about 0.8. I would just like to see what is happening. The motor is a small 12v device for a model train.
I am using a Zetex ZHB6718 h-bridge. This is a bipolar based bridge, presumably with Darlingtons, since the quoted small signal gains are typically 450. The pwm signal is applied to one side of the bridge while the other side is at 0v. The motor runs, but only slowly.