Electroencephalographic signals are employed to analyze brain activity. By being low voltage level signals, its digitalization represents a big challenge. Currently, there are several proposals and BCIs, many of them based on complicated and expensive ADCs and DSPs to collect and digitally process data. Hence, this paper presents the design and implementation of an active-filtering circuit for electroencephalographic signal acquisition in a frequency range between 0.15 Hz and 50Hz using an 8-bit AVR RISC-based microcontroller. This hardware is composed of four fundamental elements: Reception block, filtering circuit, ADC adaptation circuit, and digital communication system. This paper offers the results of board design, emulation, and implementation concerning the amplitude spectrum and its SNR value.