This low cost module measures the short-term accuracy of 60
Hz sources. A bright bargraph indicator displays variations around the
Prototype Photo The circuit is constructed around a single chip microcontroller with
a minimum of external components. A red LED blinks at 1 Hz and the bargraph
display is updated once per second with the frequency readout. The prototype
circuit requires only a +5V regulated supply and the external TTL level
source to be measured.