Inexpensive frequency counter tachometer

Posted on Feb 7, 2014

Inexpensive frequency counter/tachometer. This circuit uses a 556 dual timer to generate the gating, not-store and not-reset signals for a ICM7217 counter. One timer is an astable multivibrator using RA, RB and C to provide an output that is positive for approximately 1 second and negative for approximately 300 to 500 s to serve as the gating si

Inexpensive frequency counter tachometer
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gnal. The system is calibrated by using a 5M pot for RA as a coarse control and a 1 K pot for RB as a fine control. The other timer is a one-shot multivibrator triggered by the negative-going edge of the gating. This output at pin 9 is inverted to serve as the store pulse and to hold not-reset high. When the one-shot times out and the store goes high, not-reset goes low, resetting the counter. The one-shot pulse width is approximately 50 s with the components shown. When fine trimming with FIB care should be taken to keep the gating low time at least twice as long as the one-shot pulse width (courtesy Intersil, Inc. ).

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