açıklamalı devreler

Hülya Yıldız · Tarih: 17.05.2006, 08:52 Mesaj konusu: **açıklamalı devreler**

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Adigital frequency counter needs a
time-base generator to count the
frequency with high resolution.
Normally, a crystal-based oscillator with
divider IC chain or a similar circuit in the
form of an ASIC (application-specific IC)
is used for time-base generation. Here
we’ve presented a simple circuit for accurate
time-base generation using the readily
available 3.5795MHz crystal commonly
used in telecommunication equipment.
The 3.5795MHz crystal is used in conjunction
with a CD4060-based crystal oscillator-
cum-divider (IC1). The crystal frequency
is divided by 512 by IC1, which is
further divided by 7 by CD4017 (IC2). IC2
is reset as soon as its Q7 output goes high.
Thus the crystal frequency is divided
by 3584, giving the final output frequency
of around 998.8 Hz. This frequency can
be trimmed to exactly 1 kHz with the help
of trimmer capacitor VC1 as shown in the
figure. The 1kHz signal can be further
divided using decade counters to generate
the required time period.
EFY lab note. To generate required
gate for use in a frequency counter circuit,
the final oscillator output needs to be followed
by a toggle flip-flop. For example, a
1kHz clock, when applied to a toggle flipflop,
will generate gates with 1-sec ‘on’
period and 1-sec ‘off’ period.
This circuit is estimated to cost below
Rs 50.

ömer · Tarih: 17.05.2006, 20:10 Mesaj konusu: **slm**

teşekkürler.