Fluorescent light
simulator
for model railways
The key word for any railway modeller and his
layout is "realism", right down to the fluorescent
street lights. This project "quickie" simulates the
flicker you see when fluoros first start up, and it
can power up to 30 mini lamps.
By DARREN YATES
This is one of those circuits for the
model railway perfectionist. It's just
the shot for controlling the lamps
around your layout and will provide
a realistic "fluoro-flicker " each time
the lights are switched on - just like
real fluorescent lights. This rapid
flikering effect only lasts for a brief
period, after which the lights come on
and stay on.
The circuit should appeal most to
those who like playing "night trains";
ie, running their layout in a dimmed
room to take full advantage of the
When the circuit is turned on, the lamps flicker for a brief period & then stay on
- just like real fluorescent lamps. It will add realism to your model train layout.
42
SILICON CHIP
lighting. Best of all , the circu it is quite
simple and uses just one IC and a
handful of other components. It will
only take you about an hour or so to
build, so you'll have it up and running in no time at all.
How it works
Fig.1 shows the circuit diagram of
the Fluorescent Lamp Simulator.
When the circuit is first turned on ,
the lO0µF electrolytic capacitor at the
base of transistor Ql has no voltage
across it, so Ql is turned off.
While the capacitor is charging up
via the 680kQ resistor, pins 6, 9, 13
and 2 of ICl are all high. These pins
are used as enable inputs for the four
Schmitt trigger NAND gates (ICl a-d),
which are connected as square wave
oscillators.
ICla is connected in a conventional
manner, with a 680kQ feedback resistor from output to input, and a 0.15µF
timing capacitor from input to ground.
This gives an output frequency of
about 8Hz.
ICl b, c & d are also connected as
oscillators but in a different manner.
Instead of the feedback resistor going
from each gate's output to its input, it
is connected to the input of the next
gate in the chain; eg, pin 4 of ICl b is
connected to pin 8 of IClc via the
feedback resistor, etc.
This forms what is known as a ring
counter. The reason for this arrangement is so that the outputs of the
three gates, IClb-ICld, go high one at
a time to produce a light chaser effect.
These outputs are mixed with the
output of ICla via diodes Dl to D6 ,
which form three OR gates. Dl and D4
form one OR gate, D5 and DZ another,
and D3 and D6 the third. The result of
all this jiggery-pokey is that ICla pro-
47!!
r---+-----------4-------+-------''#No.----------4----.....- - - - - - - - - • 1 2 V
ffJ
J
1W
680k,
LAMPS
B
100 +
16VWJ
680k
01
1N914
.,.
LAMPS
05
1N914
05
B0139
0.151
C
.,.
680k
B
02
1N914
.,.
4.7k
07
B0139 C
B
E
.,.
0.15!
B
EOc
VIEWED FROM
BELOW
680k
ECB
FLUORESCENT LAMP SIMULATOR
Fig.1: when the circuit is first turned on, Ql's collector is high & this enables a
ring counter IClb-lClc & Schmitt trigger oscillator ICla. The outputs from the
ring counter are OR'ed with the output from ICla using D1-D6 & the resulting
signals then used to drive three Darlington transistor pairs to switch the lamps.
vides a degree of randomness to the
outputs, to give the lamps that flickering effect.
The OR-gate outputs are then fed to
three lamp driver transistor stages via
4. 7kQ isolating resistors. Each of these
stages consists of a BC337 and a BD139
transistor connected in a Darlington
arrangement to provide the necessary
current gain. When each output goes
high, its associated Darlington output
stage turns on and current briefly flows
through the associated lamp.
During this time, the lO0µF capacitor on Ql 's base continues charging
until it reaches 0.6V. At this point, Ql
turns on, pulling the enable line connected to the oscillator inputs low
and forcing the NAND gate outputs
permanently high. The lamps now
stay on continuously. The capacitor
charges up in 2-3 seconds which
Where to buy the kit
A kit of parts for this project is available from Electronic Toy Services, PO
Box 491, Noarlunga Centre, South Australia 5168 (Shop 2/111, Glynville
Drive, Hackham West, SA). This kit includes the PC board & all on-board
components, but does not include the lamps. The price is $14.95 plus $2.50
p&p. The PC board can be purchased separately for $5.95 plus $2.50 p&p.
Payment may be made by cheque or money order, or by phoning (08) 382
8919 and quoting a credit card number.
Note: copyright of the PC board artwork associated with this project is
retained by Electronic Toy Services.
PARTS LIST
1 PC board (available from
Electronic Toy Services)
3 12V mini lamps (eg, Jaycar
Cat. Sl-2639) plus additional
lamps (up to 30) as required
Semiconductors
1 4093 quad Schmitt trigger
NANO gate (IC1)
1 BC549 NPN transistor (01)
3 BC337 NPN transistors
(02,04,06)
3 8D139 NPN transistors
(03,05,07)
1 12V 1W zener diode (ZD1)
6 1N914 diodes (D1-D6)
Capacitors
1 100µF 16VW PC mounting
electrolytic
4 0.15µF 5mm-pitch metallised
polyester
Resistors (0.25W, 5%)
5 680kQ
3 4.?kQ
1 2.2kQ
1 47Q
MAY1991
43
·-
Fig.2: follow this diagram
carefully when installing
the parts on the PC board
& take care to ensure that
all parts are correctly
oriented. The pinouts for
the B0139 transistors are
shown on Fig.1 (mount
them so that their metal
tabs face the edge of the
board). Up to 10 mini
lamps can be wired in
parallel to each channel.
UHF HIGH GAIN ANTENNAS
antenn
existing
systems
triangul
powder
coated
receiving
elements ensures excellent UHF reception
compared to other UHF antennas of similar size
and price. Two models are available: the
for Band Four and the
S for Band Five UHF •
reception. Both models are supplied with back
reflectors to prevent ghosting as well as a
waterproof entry box designed to accept 75 ohm
coaxial cable without the need for addittional
baluns. They also have predrilled holes for
securing the tilt adjustable metal mounting
bracket in either a horizontal or vertical position.
Imported and distributed by:
Available through the following retailers:
Bernys.
Brldgepoint.
Military Road.
Mosman. 2088.
NSW. (02) 969 1966.
Ritronics.
56 Renver Rd.
Clayton.
Victoria. 3168.
(03) 543 2166.
means that the lamps only flicker on
and off for this amount of time.
Power for the circuit can be provided by the train controller supply.
A 12V 1W zener diode is used to
protect the CMOS IC against high input voltages.
By the way, if you only intend using four or five lamps per output stage,
you can do away with the BD139 transistors and just use the BC33 7 transistors to drive each set of lamps.
Construction
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44
SILICON CHIP
All components, except for the
lamps, are installed on a small PC
board measuring 73 x 63mm. Before
you begin soldering, check the board
for any shorted or broken tracks, particularly those running between the
IC pins.
Once you 're satisfied that the board
is correct, start the assembly by soldering in the resistors and diodes.
Fig.2 shows how the parts are installed. If you're not sure of the colour
code of the resistors, use a multimeter
or check the accompanying table. Be
sure to match the polarity of each
diode to the wiring diagram.
Next, install the greencap capacitors. These all have the same value, so
you shouldn't have any problems here.
When you've done that, solder in
the transistors. Again, check with the
overlay diagram to make sure you insert them correctly. The circuit diagram (Fig.1) shows the pinout details
for the transistors. Note that the
BD139s are installed with the metal
faces of their tabs nearest the edge of
the PC board. If you aren't using the
BD139 transistors (see above), install
a wire link between the base and emitter holes where each BD139 would
have gone.
Finally, solder in the IC. Check again
that you have inserted it correctly before you start soldering. When you
have finished the board, check it carefully for solder splashes to ensure that
there are no shorts between tracks or
between IC pins.
When you are connecting up the
lamps, note that they all have a common line; ie, the connection to the
+12V supply rail. It is then just a
simple case of running the other leads
from the lamps to the outputs provided on the board as appropriate.
Finally, you can either install the
board in a small zippy box or just
hide it as is under the layout table the choice is yours. Be sure to connect the power supply the right way
around.
SC
RESISTOR COLOUR CODES
Value
4-Band Code (5%)
5-Band Code (1%)
680kQ
4.7kQ
2.2kQ
47Q
blue grey yellow gold
yellow violet red gold
red red red gold
yellow violet black gold
blue grey black orange brown
yellow violet black brown brown
red red black brown brown
yellow violet black gold brown
