A Basic Voltage To Frequency Converter

This circuit operates as a basic Voltage-to-Frequency Converter (VFC) centered around the HEF4046B CMOS micropower phase-locked loop integrated circuit. While the HEF4046B is frequently used for phase-locking applications, its internal voltage-controlled oscillator (VCO) section can be isolated and utilized independently for frequency conversion. An incoming DC control voltage—which can be manually adjusted using an optional 100k linear potentiometer (VR1) across a 10k resistor (R1)—is applied to the VCO input pin of the IC. The magnitude of this analog input voltage dictates the internal charging and discharging current for an external timing capacitor, which in this design is a 100nF capacitor (C1) connected to the appropriate oscillator terminals of the HEF4046B. As the input voltage increases, the rate at which the capacitor charges and discharges changes proportionally, driving the VCO to output a square wave pulse train whose frequency directly mirrors the applied voltage level. An optional red or amber LED1 can be incorporated into the output stage to provide visual confirmation of the pulsing frequency. Additionally, an optional filter capacitor (C2) can be placed across the power rails or input lines to help suppress noise and stabilize the DC supply. Operating from a regulated 5V DC power source, the entire circuit can be easily prototyped on a standard breadboard and monitored using an oscilloscope to observe real-time frequency modulation as the input voltage varies.