Matseng soldered his Visualizer Arduino shield. You might remember these PCB as the with the cool dithered “eye” artwork on the back. The shield shows the state of the each Arduino pin – ‘Hi’ or ‘Low’:
It seems like both the hardware and firmware is ok. I just had to lower the value of a resistor connected to the Config-button a bit since it couldn’t override the SCK signal from my programmer.
The firmware can either display the logic level (high/low or floating) of all pins, or it can show the actual voltage (represented as a 8-bit value on D0-D7) on a pin that is selected by briefly pressing the config button to step through the pins.
Via the forum.