Abstract: A voltage monitoring system and a method for harvesting energy is disclosed. A system includes a ring oscillator circuit, which incorporates delay line circuit composed of series of inverting logic gates. The final inverting logic gate forms self-oscillating feedback loop by connecting its output to the input of the first logic gate. To interface with ring oscillator circuit, transistor-based voltage divider circuit is implemented. The transistor-based voltage divider circuit utilizes multiple diode-connected transistor devices, with bulk terminals interconnected to the respective source terminals. Enable signal controls final diode-connected transistor device at its gate terminal. Furthermore, a voltage-level shifter circuit is connected to output of inverting logic gates, enabling seamless integration with ring oscillator circuit. Finally, a counter circuit is linked to voltage-level shifter circuit, utilizing its output terminal.