A proven way to send an analogue signal a long distance is to transport the signal as a frequency using a voltage to frequency converter (VFC), a special circuit whose output is a frequency that is proportional to its input voltage.
In principle, it is relatively easy to send a frequency signal over a long transmission path without interference through optical, coaxial, or radio links. The frequency is then reconverted to an analogue voltage by a FVC that is usually tailored to perform its inverse function, often using a phase-locked loop (PLL). Block diagram of the project is shown in Fig. 1.
This project uses an odd approach to design and build a hobby-level VFC module using a handful of easily available and inexpensive electronic components. Author’s circuit of the VFC module wired on a breadboard is shown in Fig. 2.
Schematic diagram of the VFC module is shown in Fig. 3. Please note, a well-regulated 5V DC power source is absolutely necessary to run this VFC circuit. Heart of the circuit is the venerable CMOS micropower phase-locked loop IC HEF4046B.
The HEF4046B (IC1) includes a VCO sub-system in addition to phase comparators and other elements. It can generate a square wave with 50% duty cycle. The frequency is reasonably close to 0Hz-1kHz range, which is curbed by the 100nF capacitor (C1) and the 10k resistor (R1).
This project will be published in a few weeks. If you want to access it now, refer to Electronics For You’s October 2022 Issue–print or ezine edition.