Silicon Chip – July 2019

siliconchip.com.au Australia’s electronics magazine July 2019 79

enough to be cut and folded easily with
hand tools, but heavy enough to form
a sturdy box for the signal generator.
Several holes need to be drilled and
cut into the panel for the controls, slide
switches, regulator and the LCD. Aside
from standard drills, a metal nibbling
tool is ideal for cutting out the rectan-
gular holes.
Final finishing during fitting can be
completed with a fine file.
The completed PCB is mounted us-
ing spacers and 3mm machine screws.
It’s best to line it up with the holes in
the lid to figure out exactly where it
will sit in the case before marking and
drilling out the three mounting holes
in the base.
Alternately, as in the prototype,
the signal generator PCB can be held
onto the front panel using the rotary
encoder nut, although it would prob-
ably be better to attach using at least
one tapped spacer too.
Small self-tapping screws are used
to hold the cover to the base of the
box. Once you’ve cut and bent the
sheets, rivet or screw the 7805 regu-

lator (REG1) onto the metal cover just

before the final step of screwing the

cover to the base.

The front panel artwork is shown in

Fig.8 above. This can be printed on a

colour printer and covered with trans-

parent self-adhesive plastic film.

Trim the artwork to cut out the holes

for the various controls and display

and test-fit onto the completed met-

al-work.

The most reliable method to fix the

artwork in place is to spray the rear

side of the artwork with adhesive spray

obtainable from most stationary shops.

While tacky, press the panel artwork

into place. Remove the rotary encoder

nut before attaching the front panel,

then re-attach it on top.

3D-printed knobs

Suitable knobs may be available

from normal suppliers. However, I de-

signed the knobs for my Signal Gen-

erator using DesignSpark Mechanical

and 3D-printed them from grey PLA

filament.

My knob STL files can also be down-

loaded from the SILICON CHIP website

for those wishing to print their own

knobs. They press into place and hold

securely.

It’s useful to add four self-adhesive

rubber feet to the rear of the enclosure.

This prevents any sharp corners of the

aluminium box from scratching the

bench and helps to keep the oscillator

in one place on the workshop bench.

Using the Signal Generator

Briefly press power switch S3 to

turn the signal generator on. The dis-

play will show a start-up message, then

after a short delay, the normal screen.

If you cannot see any text on the

display, adjust VR1. This sets the LCD

contrast. You can see examples of the

various possible displays in the first

article in this series, published last

month.

The display shows the current out-

put frequency and operating mode; the

generator always starts at 10.000MHz

in CW (unmodulated) mode.

The display also features a frequen-

cy ‘dial’ which covers a 1MHz span

Fig.8: this panel label can be photocopied here or downloaded from the SILICON CHIP website (as a PDF) and then printed.
You could then laminate it, cut out the display and switch holes, then cut it to size and glue it to the outside top of the case.

ZL 2 PD HF/VHF AM/FM/CW Scanning Signal Generator

siliconchip.com.au

SILICON

CHIP

-20dB -20dB -20dB -20dB

0-20dB

RF OUT

SCAN

RF OUT

MODE

POWER

BAND

0-50MHz 70-120MHz

DC IN

TUNE STEP