AN795

© 2002 Microchip Technology, Inc.

DS00795A-page 8

FREQUENCY METER

The TC9400 will convert any frequency below 100kHz into an output voltage, which is linearly proportional to the input frequency. The

equivalent frequency is then displayed on an analog meter. If the incoming frequency is above 100kHz, a frequency divider in front of the

TC9400 can be used to scale the frequency down into the 100kHz region.

Analog Meter

TC9400

F/V

FIGURE 17: Frequency meter.

TACHOMETER BAR GRAPH DISPLAY

A tachometer can be constructed by using the TC9400 in the F/V mode to convert the frequency information (RPM) into a a linearly-

proportional voltage. This voltage is then compared to one of "n" comparators (8 in this example). When the voltage exceeds the trip

point of a comparator, the respective LED lights up and will continue to stay lit as long as the voltage exceeds the trip point. This gives

a bar-graph-type display, with the height of the bar being proportional to RPM.

FIGURE 18: Tachometer bar graph display.

Display

Visible

LEDs

Two TC1027

Quad Comparators

TC9400

F/V