This is the Didel Logic Pen - or short: the LoPen, a greatly helpful tool when you need to quickly check the logic level somewhere on a PCB or chip directly.
A logic probe or logic tester shows the state of a logic signal. If that state is zero or one, a simple LED can be used. A logic signal can also be floating, that is not connected or in tri-state mode. It can can also be a short pulse your LED will not see, or it is pulsing too fast for your eyes.
The LoPen takes care of these situations: A yellow LED shows floating signals. Visible blinks are given for glitches as short as 100 nanaoseconds and a slow blink shows a high frequency signal.
The LoPen can be powered with 2-6VDC, a diode serves as polarity protection.
Note: This is the kit version of the LoPen which is slightly larger than the Mini LoPen. Comes as an easy to assemble PTH soldering kit