Hello all,
     I hope that I can get some help. I am attempting to build a=20
frequency counter. I have the input amplifier, counter circuits, and the=20
time base built. I am having trouble building a gating circuit. The=20
input consists of a diode limiter, 2n4401 amplifier, a capacitor to=20
eliminate any dc offset, and a 74hct14 schmitt inverter to condition the=20
signal.         The display is eight CC seven segment LEDs driven by=20
eight CD4511 BCD to seven segment latching decoder drivers.
     The timebase is a four MHz 2n3904 crystal oscillator that is=20
amplified by a 2n4401 transistor and then fed to a 74HC4060 14 stage=20
binary ripple counter. This conditions and steps the 4 MHz signal down=20
to 250Hz. I then feed this to two 74LS390 decade counters. This gives me=20
10Hz, 5Hz, 2Hz, and 1Hz signals. These are fed to a 74HC4053 triple dual=20
channel multiplexer.
     These are connected so that I can turn the signal off which would=20
allow the counter to run in free running mode or to select one of the=20
four frequencies of 10, 5, 2, or 1Hz for controlling the gate timing.
     I can't come up with a gating circuit that will provide the=20
necessary trigger window, the latching signal, and the reset pulse.=20
Could someone please help me?
      I also thought about using a PIC to supply the time base, the=20
reset pulse, the gating window, and the latching signal, but I don't=20
even know where to begin but I am sure that it could be done pretty=20
easily with the PIC. That would eliminate the timebase, the dividers,=20
and the switch. One chip would replace two transistors, two 74ls390s,=20
and a 74HC4052 multiplexer. Does anyone have any ideas or thoughts on=20
any of this?
Thanks,
rich!
--=20
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