 | Author | Message | | | eric | | Posted: Thu Oct 05, 2006 2:31 am Post subject: Pulse generator with variable duty factor | | | | Site Admin Joined: 01 Jan 1970 Posts: 311 | W. Dijkstra 048
The duty factor of the pulse
generator in the diagram is variable
in 10% steps from 10% to
90%.
With the aid of thumb wheel
switch S1, a 4-bit word, S, is
added to one input of IC1 and
to IC2. Circuit IC1 is a full
adder, while IC2 functions as a
switch. The binary equivalent of
5 is applied to the other input of
IC1. The output of IC1 is linked
to the second input of IC2.
The output of IC2 is applied
to the programmable input of
up/down counter IC3 via
bistable IC4a. The terminal
count output of IC3 clocks IC4a
via transistor T1. The output of
IC4a switches the counter from
up to down and at the same
time links data S or data S+5 to
the programmable input of the
counter and vice versa.
Imagine that the non-inverting
output (pin 1) of IC4a is
high. Counter IC3 then counts
downward and the programmable
input is linked with S, which
is, say, in position 6. The
counter counts downward until
it reaches 0, which is after six
input pulses. The terminal
count output goes low, whereupon
the non-inverting output
of IC4a also goes low, IC3 starts
counting upward and is programmed
with data S+5 (here,
11), so that the terminal
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