Abstract— Some measures of merit of an inverter system are the total harmonic distortion and the efficiency figures. On one hand, we have square wave and modified square wave inverters that have high efficiency and total harmonic distortion (THD) figures. On the other hand, there are the true sine wave inverters that have low THDs and relatively low efficiency figures at high output power levels. In this work, a five level waveform that can be synthesized efficiently was analysed for low distortion figures, and a THD figure of 1.25% was obtained. A microcontroller-based inverter circuit was designed to synthesize this waveform from a 12 volts d.c source. The microcontroller firmware and hardware were developed using MicroC® and Proteus® softwares respectively. The developed circuit generated a 50 Hz sinusoidal output waveform from a 12 volts battery source after filtering with an LC low pass filter.

The development of technologies for detecting or preventing drowsiness at the wheel has been a major challenge in the area of accident avoidance systems. Due to the hazard that drowsiness presents on the road, methods need to be developed for its early detection. This study implements a Haar cascade technique on a Raspberry Pi module and evaluates the performance of the developed system. The results obtained from the evaluation of the standalone embedded system show that a precision of 80.11% and recall (sensitivity) of 99.81% were achieved. The results of the system usability test (based on an administered questionnaire) reveal that the mean System Usability Scale (SUS) score for the 20 participants is 77.38, with a standard deviation of 9.40. The minimum and maximum score are 57.50 and 92.50, respectively. The mean SUS score of 77.38 indicates that user satisfaction is adequate.

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A number of failure mechanisms can result in the damage of loudspeakers that are directly connected to an audio power amplifier system. One of such failure modes occurs when the amplifier circuit develops an output d.c voltage, in which case, the loudspeaker coil will be damaged by overheating. D.c offset detection circuits, usually based on simple transistor circuits are normally used to protect the loudspeaker against this failure mode. However, as effective as they are, these circuits can fail in ways that can result in loudspeaker damage. In this work, a microcontroller based circuit that monitors the critical components of a loudspeaker d.c detection circuit, namely the switching transistor and the isolating relay circuit was developed. The hardware of the developed circuit was modelled with Proteus® software and its firmware was written using MikroC® software. The modelled circuit successfully detects the presence of d.c signals and also reports the states of the isolating relay and the switching transistors when these components fail.

Abstract-A power inverter circuits is normally designed to meet its design specifications when the applied input DC voltage is within specified tolerance limits. Thus, single input inverters are usually specified to work from a DC source having a fixed nominal voltage. This limits the usefulness of the inverter circuit when a DC source having the specified nominal voltage is not available. In this work, a modified square wave inverter system that is specified to work properly from batteries with nominal voltages of 6, 12, 18 and 24 V was designed. A model of the microcontroller-based circuit was developed with Proteus® software and its firmware was written in C language using the MicroC® development tool. A prototype of the circuit was constructed and then tested. The constructed circuit was found to work properly by producing a 50 Hz modified square waveform when it was powered from batteries having nominal voltages of 6 V, 12 V, 18 V and 24 V.