Design and Analytical Performance Evaluation of a Low-Cost Microcontroller-Based Digital Oscilloscope

Commercial digital storage oscilloscopes remain costly for many teaching laboratories in developing countries. This study presents the design, construction and analytical performance evaluation of a low-cost digital oscilloscope based on the ATmega328P microcontroller, a 128 × 64 graphical liquid crystal display and a switched-mode power supply, built in 2023 at a component cost of ₦51,810 (about US$110). The instrument accepts signals of up to 250 V AC directly through an on-board attenuator, removing the external step-down transformer required by an earlier design. Performance was evaluated from the firmware source code, the design records and recorded functional tests. Although the analogue-to-digital converter is 10-bit in hardware, the firmware reads only its eight most significant bits, giving an effective resolution of 19.53 mV, a quantization uncertainty of ±9.77 mV and a theoretical dynamic range of 49.9 dB. Nine time-base settings from 0.02 to 10 ms/div correspond to nominal sampling rates from 0.8 kS/s up to the converter limit of about 308 kS/s, giving Nyquist limits from 400 Hz to about 154 kHz and a practical display bandwidth of about 30 kHz. In tests with the 220 V, 50 Hz mains supply, the instrument displayed stable sinusoidal traces and reported 50 Hz at the 2, 5 and 10 ms/div settings, consistent with the analysed frequency resolution of 1.25–6.25%. The analysis also shows that reading the full 10-bit result would improve resolution to 4.88 mV and dynamic range to 62 dB without any hardware change.