This paper presents a miniaturized didactic device for experimenting with the feedback control of air pressure in a vessel, called the PressureShield. The apparatus is built on a custom extension shield for Arduino R3 compatible microprocessor boards, utilizing widely available off-the-shelf components and 3D-printed parts, resulting in an exceptionally low-cost hardware that can be manufactured under 20 e. The device was created within a larger initiative AutomationShield, which aims to create open-source low-cost educational tools intended to aid control systems and mechatronics education via hands-on experiments or even aid conducting research on a budget. The hardware and software specifications briefly introduced in this paper are freely accessible on the project's GitHub wiki page, making it possible for anyone to reproduce, use, or even improve the PressureShield. In addition to hardware design with downloadable project files, we also present available application programming interfaces and outputs of some demonstration examples.