A prototype of a printed circuit board (PCB) with radio frequency electromagnetic compatibility specifications is designed using the top-down methodology for the two-layer Internet of Things with free open-source hardware and software, using the following techniques: requirements, analysis, modular design, schematics, manufacturing and functional testing. The study of the influence of the design parameters is carried out applying the standards of the Printed Circuit Institute and the characteristics of the technological production process for a free multiplatform for wireless networks. Finally, functional tests of the universal asynchronous transmit and receive (UART) communication with the microcontroller, the radio modules, the general-purpose input and output pins, and the over-the-air (OTA) configuration are performed to program the board wirelessly, without the need of a universal serial bus (USB) interface.