After I broke my BeagleBone Black and could not order a new one anywhere without crazy lead times I got a RaspberryPi. Powering it off USB caused me some headache so it was time to fire up the USB Test Card.
The picture shows the RPi in the front. Power comes from right from a USB charger and passes through the USB Test Card in the center. The Voltage and Current outputs are connected to the Oscilloscope.
Voltage looked good, but the thing still did not start properly. A quick check with a Multimeter showed a big voltage drop from USB Test Card VBUS to RPi’s 5V header. A cheap Micro USB cable is nothing better than a cheap and underrated power supply!
With the now working setup I took some Scopeshots of the RaspberryPi running headless and idle raspbmc.
The first picture shows the thing booting and in the second we can see some periodic action. If this would be a device I am developing I would definitely want to understand where this periodic jumps are coming from and why there is a break during startup.
Maybe the RaspberryPi will finally motivate me to get RS232 or GPIB output of my ancient Tektronix TDS224 working.