Micro-controller based frequency to digital converter for interfacing frequency output sensors

We present the design and testing of a 16-bit frequency to digital converter, based on AT89C51 micro-controller, for use in sensing applications. The system generates digital equivalents of frequencies by counting negative transitions of transistor transistor logic signal applied to a designated input of the microcontroller's on-chip counter. The system digitizes frequencies of signal generated from a frequency generator, while the digitized data are logged in a personnel computer via printer port by using a LabVIEW program. The system is found to have a linear response over a large dynamic range of conversion, and its resolution is tunable down to 1.6 Hz. The proposed system can be used as interface circuit for frequency output sensors without relying on frequency to voltage converter and analog to digital converter.