Two low-cost integrated circuits can be combined to create a
simple digital frequency meter. The combination of a frequency-to-
voltage converter (FVC) and a dual-slope, analog-to-digital display
converter (ADC) makes a small 2-chip frequency meter that can be
run from one 9-volt battery.
The ADC (TC7136) generates the voltage required by the FVC
(TC9400) with internal regulators. The TEST output of the TC7136
is regulated to 5 volts below the positive battery terminal (V+) and
the ANALOG COMMON output is regulated to 3V below V+. The
TC7136 is designed to directly drive a 3-1/2 digit, non-multiplexed
LCD display so no digital conversion is required.
The test voltage is used as the reference supply for the TC9400 and
ANALOG COMMON serves as the "ground" for the comparator
and the integrating amplifier. AN37
TC7136/TC9400 ……
