As described in the October 2017 DIYODE magazine.
This logic probe will help you diagnose and troubleshoot your 3.3V or 5V circuits, including Arduino and Raspberry Pi projects. It indicates a logic low or logic high state on the green and red LEDs, and shows a shift between states on the orange LED. There is also a switch for TTL or CMOS circuits. Kit supplied with double-sided screen printed PCB and specified parts. We’ve even thrown in the paperclip for the probe tip. You'll need to 3D print your own case though, for which you can download the print file from the DIYODE website.
Raspberry Pi is a trademark of the Raspberry Pi Foundation