■ FIGURE 5.
connected to the case. The external
input was placed on the rear panel,
assuming infrequent use.
If you don't implement the
complete circuit, be sure to pull up
or pull down any unused inputs (e.g.,
if the crystal oscillator is not loaded,
a 10K resistor from the crystal
oscillator output on the PCB to either
+5V or Gnd will keep U2 pin 1 from
floating).
After the PCB is loaded,
temporarily wire in the ADJ pots and
verify the functionality of the circuit
(just in case there is a solder bridge
or other problem). Using temporary
connections (clip leads/wires), check
all switch functions.
Using the Pulse
Generator
The pulse generator is used to
44 February 2013
create logic level signals that are
needed to check out electronic
projects. It can be used during the
design, development, or checkout of
logic or microprocessor circuits
where external inputs need to be
simulated.
I have recently used it on
projects such as an anemometer, an
automobile over-speed alarm, and a
stepper motor controller.
The pulse generator typically
provides pulses simulating a "logic
clock" but can also be used in less
obvious ways. For example, a 1 Hz
frequency can easily and accurately
be obtained by setting the frequency
to 1.000 kHz and then changing the
"range" switch by three decades to
get to an output of 1 Hz.
Another use that may not be
obvious is to put the generator in the
"single" mode and flip the polarity
switch (±); you now have a logic level
that can be changed without the
"contact bouncing" that occurs when
connecting and disconnecting a
clip lead.
