thru-hole parts as the power planes
are heatsinking.
One of the more difficult parts
of any homemade equipment is
creating a good looking front panel.
I chose a minimalist approach, i.e.,
just enough lettering to identify the
various controls and switches, and
no more.
The front panel is drilled before
the lettering is applied, eliminating a
lot of planning and coordination of
the exact location of the switches
and potentiometers. That is, the
holes for the switches do not have to
be placed in precise locations to
match the lettering; the lettering is
placed after the holes are drilled.
Using self-adhesive paper (Avery
labels), I print the lettering with an
inkjet printer and then seal the print
with a spray-on fixative. The lettering
is then cut to size and applied to the
front panel. This technique creates a
functional and good looking front
panel with minimal effort. (Or, you
can use services from companies
such as
FrontPanelExpress.com.)
Feel free to rearrange the front panel
to suit your needs.
Any single pole rotary switch
with nine or more positions can be
used. A common variety found in the
hobby/surplus market is the one
pole/12 position type. The specified
switch (Mammoth Electronics #820-
1P2-12T) has a stop feature that
allows rotation to be limited to the
nine positions needed for this
project. (Mammoth Electronics will
give a 15% discount if you mention
Nuts & Volts.)
If you choose to use a switch
without a "position stop," connect the
extra positions together with the first
or last position so the circuit outputs
a signal when one of the extra
positions is selected.
Note: When wiring the
frequency range switch (SW1),
increasing frequency with clockwise
rotation requires the switch to be
wired in the opposite direction of the
schematic numbering: f1 goes to
switch position 9; f2 goes to switch
position 8; etc.
PARTS LIST
QTY DESIGNATOR DESCRIPTION
7 C1- C3, C5, C7, C9, C10 0.01, radial ceramic, 50V, 10%, XR7
32 C4, C6, C8, C11-C39 0.1, radial ceramic, 50V, 20%, Z5U
4 C40-C43 22 µF, 10V
1 C44 22 pF, radial ceramic, 100V, 5%, C0G (NP0)
1 Ctf 82 pF, radial ceramic, 100V, 5%, C0G (NP0)
1 Ctp 47 pF, radial ceramic, 100V, 5%, C0G (NP0)
1 D1 1N4148
1 OSC 10 MHz
1 R1 200, 5%, 1/4 watt
1 R2 220, 5%, 1/4 watt
3 R3, R4, R11 1K, 5%, 1/4 watt
1 R5 100K, 5%, 1/4 watt
1 R6 200, 5%, 1/4 watt
1 R7 220, 5%, 1/4 watt
1 R8 10K, 5%, 1/4 watt
2 R9, R10 51, 5%, 1/4 watt
4 RN1-RN4 10K Eight-pin resistor network-bussed
2 U1, U5 Schmitt trigger inverter - SOT- 23
4 U2, U3, U7, U10 Configurable multi-function gate - SOT- 23
2 U4, U6 Dual FET bus switch - SOIC
2 U8, U9 Dual J-K flip-flop - SOIC
8 U11-U15, U17-U20 Dual decade counters - DIP
4 U15, U16, U21,U22 Quad bus buffer gate - DIP
1 U23 Hex inverter - DIP
1 U24 Dual peripheral drivers - DIP
Panel Mount Components
1 LED1
1 LED2
2 POT1, POT2
2 SW1, SW2
1 SW3
1 SW4
3 SW5-SW7
3
2
2
2
1
1
Green
Red
10K audio
Rotary switch, SP- 12 pos
Toggle switch, SPDT on-none-on
Momentary toggle switch, SPDT on-(on)
Toggle switch, SPDT on-on
BNC or RCA phono jacks
Grounding lugs
Knob/range
Knob/adj
Instrument case
Power supply, 5V/0.5A regulated
A more detailed Parts List with both manufacturer and distributor part numbers
is available at the article link.
The potentiometer housings
need to be grounded to stabilize
stray capacitance in the oscillator
adjustment circuits. Start by scraping
the paint on the inside of the front
panel around the potentiometer's
mounting hole. Then, use a
grounding lug with a star washer
when mounting the pot. Connect
the lug to ground using the
corresponding hole provided on the
PCB (GFp and GPp). If you don't
have a grounding lug, you can wrap a
piece of bus wire around the bushing
and use a regular star washer.
Note: Capacitor C44 is mounted
at the pulse width ADJ potentiometer
(POT2) between the potentiometer
and the ground lug (wire); see
Figure 5. A grounding lug is specified
in the Parts List. Wiring to the
switches is not critical. Just hook
them up neatly and you will be fine.
(Refer back to Figure 4.) The LEDs
are held in place with glue.
Either RCA phono jacks or BNC
connectors can be used for the
outputs. The phono jacks are much
less expensive, and sufficient for most
uses. Wiring to the outputs should be
short and neat twisted pairs.
The outer ring of the connectors
should also be connected to the case
by removing the paint and using a
star washer.
When mounting the PCB, use
metal stand-offs and star washers so
that the ground plane (top side) is
February 2013 43