Design of a Signal Conditioning Circuit for Electromyography in a Rehabilitation Engineering Laboratory at a Nigerian University

Surface electromyography is a foundational signal acquisition modality in rehabilitation engineering research, and the development of locally built signal conditioning circuits supports laboratory capacity building in Nigerian biomedical engineering programmes. This study designs and validates a signal conditioning circuit for surface electromyography acquisition intended for use in a rehabilitation engineering laboratory at Nnamdi Azikiwe University, Awka. The circuit employs a three-electrode differential configuration, an INA118 instrumentation amplifier providing an input gain of one thousand, a cascaded Sallen-Key bandpass filter architecture selecting the 20 to 450 Hz EMG frequency band, a 50 Hz twin-T notch filter, and a final gain stage adjustable from unity to ten for full-scale output matching to a twelve-bit ADC input range. Full-wave rectification and moving average envelope detection processing were implemented in the output stage for amplitude representation. The circuit was fabricated on a double-sided PCB and housed in an aluminium enclosure with shielded cables and Ag/AgCl disposable surface electrodes. Performance characterization confirmed a common mode rejection ratio above 90 dB, input impedance above 10 megaohms, frequency response within plus or minus 3 dB of the target passband, and noise floor below 1 microvolt root mean square. Functional testing on ten healthy volunteers measuring biceps brachii EMG during isometric elbow flexion tasks confirmed expected signal morphology and amplitude-force relationships. The study documents the circuit as a replicable laboratory resource for Nigerian biomedical engineering departments. Keywords: electromyography, signal conditioning, rehabilitation engineering, instrumentation amplifier, university laboratory.