Stand-Alone DDS Unit
Working with SMD ICs can be a
challenge, especially the attenuator
IC. I strongly recommend that you
have a soldering iron with a very
small tip and some very thin solder.
You should also work using a
lamp with a magnifying lens. I have a
lamp with a 3X magnifying lens, but
sometimes wish it were 5X. When
soldering the SMD ICs, the method
I use is:
• Tin the pads on the PCB — make
sure there are no solder bridges!
• Align the IC on the pads making
sure ALL the leads line up.
• Use a strip of plastic electrical tape,
cut thin, to fasten it in place.
• Use very thin solder and an iron
with a very thin tip to solder it.
• Use solder wick to remove any solder bridges.
You do not have to use the same
method of construction as I did with
the headers and sockets. I prefer
them so that I can easily take apart
the system pieces. You can solder
wires directly to the PCB instead of
using any of the header/socket pairs.
If you do use the connectors, you will
need to have either a crimp tool for
the pins or a pair of small needle-nose pliers to use. I used pliers and
did not have any trouble. Both the
headers and sockets need to be cut
to size. This can be done easily with
a utility knife.
I cut the opening for the LCD
using a Dremel tool. As it turns out, I
cut my opening larger than required
because I wanted the LCD to be
close to the top surface of the box.
You may need to drill a new
mounting hole for the voltage
regulator. Some 7805s are different
sizes with the hole further from the
pins. I did not use a heatsink, but you
can if you wish — there is room for a
The crystal oscillator has pin 1
closest to the edge of the board.
Make sure you solder both
sides of the components which
have PC traces on the top. It
helps if you do not mount the
leaded components right up
against the PCB.
When mounting the sockets,
make sure you do NOT mount
them right up against the PCB so
that you can solder the pins which
have connections on the top side.
I soldered 6” wires onto the
LED and then soldered the wires to
the PCB. This allows you to mount
the LED just about anywhere on
the cover. Try to drill the mounting
hole just large enough for the body
of the LED and not so large that it
allows the bottom lip to pass through.
I usually use Goop to glue LEDs to a
LCD: Note that the schematic
shows an extra pin at location 2.
The correct wiring for the LCD to the
connector is shown in Table 1.
1, 5, 7, 8, 9, 10
No connection (VEE) this
can be used for contrast
control if desired
■ TABLE 1
I “daisy-chained” the ground connection at the LCD using a long piece
of bare wire with sleeving pushed
onto it between pins 1 and 5, and
5 and 7.
You may need to drill mounting
holes in the PCB, depending on
how you choose to mount it in your
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