In this picture an iPad 2 and Oscium’s handheld oscilloscope are setup to measure the signals of a simple USB memory stick. Anyone who’s ever had to transfer their files between computers, like bringing a presentation to school or bringing work material home, can appreciate the convenience and security a USB memory device can offer. USB drives have replaced floppy discs, rewritable CD-ROMs and DVD-ROMs, and even the clever email-to-self data transfer that was the norm when broadband internet first became widely available. There are a number of things that endear USB drives to computer users these days. First and foremost, there are no moving internal parts so they are extremely portable and robust, and less susceptible to vibration damage than traditional PC hard drives. Next, USB drives are incredibly easy to use; no external power supplies to lug around and the connector design makes plugging them effortless.
Preparing a USB cable for probing signals
One of the easiest ways to get access to a USB drive’s analog and digital signals is to use a sacrificial cable between the drive and the computer. As shown in the picture, with the cable insulation and shielding removed, the individual wires can be used as probing points. Oscium’s iMSO-104 device ships with several digital probe leads and one analog scope probe lead. Clipping these probes onto the exposed signal wires is a way to make accurate, repeatable measurements. It takes some extra work up front, but it’s better in the end to use good probing points and make the measurements once with confidence than to get questionable results quickly by taking shortcuts.