This low cost module measures the short-term accuracy of 60
Hz sources. A bright bargraph indicator displays variations around the
Circuit Diagram The circuit is constructed around a single chip microcontroller with
a minimum of external components. The PORT-A output pins are expanded to
control twenty LED's through a BCD-to-decimal decoder/driver, with software
multiplexing between the two display units. A 2.4576 MHz crystal oscillator
also serves as a timebase for frequency measurements.