This is only a preview of the February 1993 issue of Silicon Chip. You can view 54 of the 104 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "Build The Electronic Cockroach":
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SIMPLE PROJECTS FOR
MODEL RAILROADS
Most model railroad layouts are
fairly basic but by spending just a few
dollars and a little time with a soldering iron, you can make your layout far
more realistic and interesting. These
three circuits are easy to build and
can be added to virtually any model
railroad layout.
1. Train Controller
Our first circuit is for a Low-Cost
Model Train Controller with simulated inertia - see Fig.1. Many model
railroad sets come with a simple rheostat controller but these give poor lowspeed running characteristics. They
also give rise to jack rabbit starts and a
model that slows or even stalls on
curves and gradients.
Unlike a rheostat controller, the circuit of Fig.1 behaves as a constant
voltage source at any given throttle
setting and this gives much improved
control at low running speeds. In particular, starting is much smoother and
the model no longer stalls or slows
when the going gets a little tough. Of
course, a pulse power controller gives
even better control but is much more
expensive than the controller described here.
As a bonus, our low-cost controller
26
SILICON CHIP
These three low
cost projects will
enhance the
appeal of any
model railroad
layout. They
include a low-cost
train controller, a
traffic lights
simulator & a
points controller.
By TERRY MOWLES
provides simulated inertia and braking. This is just a fancy way of saying
that the train adjusts its speed gradually when you vary the throttle and
slows gradually when the brakes are
applied, just like a real train. A couple of preset pots allow you to adjust
the amount of inertia to suit your layout.
How it works
Fig.1 shows the circuit details. It's
basically a beefed-up version of the
controller published in the November
1990 issue. The original circuit could
supply up to 1.2A whereas this new
version can supply up to 3A. This is
useful if you want to multiple-head
locos, particularly if they have smoke
generators, lighting and sound generators.
Power is derived from a 3A 12V AC
source (eg, via a mains transformer)
and this is rectified by diodes D1-D4
to provide about 17V DC. Alternatively, the bridge rectifier can ,be bypassed and the unit operated from a
12-18V DC source. This voltage is then
tapped off by throttle control VRl and
applied to the base ofQl via Sla, D5,
VR2 and a series 5.6kQ resistor.
Ql and Q2 form a Darlington output stage and this is forward biased as
soon as the voltage on Ql 's base
reaches 1.3V. Q2 then conducts and
supplies voltage to the track via a
0.22n 5W resistor. Double pole switch
B
12-18VAC
05
1N4007
SPEED
VR1
5k
0
INERTIA
VR2
1k
EOc
VIEWED FROM
BELOW
0
PLASTIC
SIDE
m
BRAKE
S1a
0
B
A~K
ECB
47 +
25VW_
S1b
+
4700
25VW-
FORWARD
S2a
4700
REVERSE
BRAKE LEVEL
VR3
1k
FORWARD
S2b
TO
TRACK
REVERSE
LOW COST 3A TRAIN CONTROLLER
Fig,1: the circuit uses Ql & Q2 to buffer the output of throttle control VRl. Q3 provides overload
protection by reducing the drive to Ql when the voltage across the 0.22Q resistor reaches 0.65V.
S2 provides forward/reverse switching by swapping the supply polarity
to the track.
Q3, LED 1 and the 0.22Q resistor
provide overload protection. Normally, the voltage across the 0.220
resistor is less than 0.65V and Q3 has
no affect on the circuit operation.
When a short circuit occurs, the output current shoots up until there is
about 0.65V across the 0.220 resistor.
Q3 then turns on and reduces the
drive to Ql, thus limiting the output
current to about 3A. LED 1 indicates
that an overload has occurred.
VR2 and its associated 4700µF capacitor provide simulated inertia for
the throttle. This inertia effect occurs
TO TRACK
a~
S1
s2[
~
~
because it takes t1me for the capacitor
to charge or discharge to its new level
each time the throttle is varied. D5
prevents the 4700µF capacitor from
discharging through VR1 when the
throttle setting is reduced.
VR3 and the 4700µF capacitor provide the braking inertia. When braking switch Slb is closed, Sla opens
and the 4700µF capacitor discharges
via the 4700 resistor and VR3. This
gradually reduces the voltage on the
base of Ql so that the train slows to a
stop. When the brake is subsequently
released, the train builds up speed to
its previous setting (assuming that VR1
is not touched in the meantime).
Note that it is not necessary to reFig.2: wire up the Thain
Controller as shown in
this diagram, The circuit
shows the pin connections
for transistors Ql, Q2 &
Q3. Note that Q2 should
be fitted to a large finned
heatsink for cooling.
duce the throttle to zero before applying the brakes. That's because Sla
switches the throttle out of circuit
when braking is applied.
Building the controller
Fig.2 shows the wiring details for
the controller. Mount the parts on the
TRAIN CONTROLLER
PARTS LIST
1 PC board, 106 x 48mm
1 5kO linear potentiometer (VR1)
2 1kO PC-mounting trimpots
(VR2,VR3)
2 DPDT miniature toggle
switches (S1 ,S2)
1 finned heatsink (see text)
1 TO-3 mounting kit (mica washer
plus insulating bushes)
Semiconductors
1 BD139 NPN transistor (Q1)
1 2N3055 NPN transistor (Q2)
1 BC337 NPN transistor (Q3)
4 1N5404 silicon diodes (D1-D4)
2 1N4007 silicon diodes (D5,D6)
1 red ~ED (LED 1)
Capacitors
1 4700µF 25VW PC electrolytic
1 47µF 25VW PC electrolytic
Resistors (0.25W, 5%)
1 5.6kO
1 4700
10.2205W
FEBRUARY
1993
27
It's also possible to bolt the transistor directly to the heatsink, provided
that you make sure that the heatsink
does not touch any other component.
That's because the heatsink will now
float at the full supply voltage if there
is no isolation.
2. Traffic Light Simulator
The Train Controller PC board can be hidden under the layout, while the
controls can be mounted in a small plastic case to give a walkaround throttle
or they can be mounted on the main console.
If you intend operating the unit from
a DC source, install D1-D4 anyway so
that the supply can be connected with
either polarity. The 5W resistor should
be mounted about 5mm proud of the
T03
-....;;;:::.;;;;:;~;:::;::;:;;::::;;:~ DEVICE
board, so that the air can circulate
beneath it to provide additional coolMICA
ing. We mounted the LED directly on
~WASHER
the board but it could also be mounted
~
elsewhere (eg, on a control panel) and
C
connected by flying leads.
C>
C>
HEATSINK
C
Be sure to install the LED with the
correct polarity, otherwise the overload protection circuitry won't work
~ INSULATING
~ BUSHES
(its anode lead is the longer of the
two). Use medium-duty hook-up wire
tfltJ-R<at>
for the connections to the power supS~~~EA~
ply, track and switch S2, since these
<at>
<at>w~m~s
leads carry currents up to 3A. The
remainder of the wiring (ie, to the
©>
LED, Sl and VR1) can be run using
<at>NUTS
rainbow cable or light-duty hook-up
Fig.3: here are the mounting details
wire.
for Q2. It should be isolated from the
Finally, power transistor Q2 must
heatsink using a mica washer &
be mounted on a large finned heatinsulating bushes.
sink, since it dissipates quite a lot of
power. Fig.3 shows the mounting dePC board exactly as shown, taking . tails. Note that the transistor is electricare to ensure that all polarised parts · cally isolated from the heatsink using
are correctly oriented. In particular,
a mica washer and two insulating
note that the metal face of the BD139 bushes. Smear all mating surfaces with
(Ql) faces towards the 4700µF capaci- heatsink compound before bolting the
assembly together.
tor.
e
s~::~:~iF
28
SILICON CHIP
Fig.4 shows the circuit for the Thaffic Light Simulator. This was first published in SILICON CHIP in November
1989. It drives green, red and yellow
LEDs to accurately simulate traffic
light cycles at an intersection.
555 timer IC1 is wired as an astable
oscillator and this provides a clock
signal for IC2, a 4017 decade counter.
IC2 's 0-9 outputs go high in turn on
each successive clock signal and drive
several sets of OR gates made up by
diodes D1-D20. These OR gates then
drive transistors Q1-Q6 to control the
traffic light LEDs (LEDs 1-12).
Note that each transistor drives two
LEDs of the same colour, one for each
opposing light set.
When pin 3, pin 2 or pin 4 of IC2 is
high, Ql turns on and lights LEDs 1 &
2 (green) for one set of lights. Q4 will
also be turned on during this time
TRAFFIC LIGHTS
PARTS LIST
1 PC board, 92 x 78mm
9 PC stakes
Semiconductors
1 555 timer (IC1)
1 4017 decade counter (IC2)
1 7805 3-terminal regu lator
(REG1)
6 BC548 NPN transistors (0106)
4 green LEDs (LED1 ,2, 11, 12)
4 yellow LEDs (LED3,4,9, 10)
4 red LEDs (LED5,6,7,8)
20 1N914 silicon diodes (D1 D20)
1 1N4007 silicon diode (D21 )
Capacitors
1 220µF 25VW PC electrolytic
1 100µF 16VW PC electrolytic
2 10µF 16VW PC electrolytic
1 0.1µF metallised polyester
Resistors (0.25W, 5%)
6 100kO
6 4700
1 82kO
1 2200
1 4.7kO
1 1500
100k
~
~
16
~
~
D4
1N914
1
2 4
7
Vk
s
~
IC2
4017
D5
10
4
5 1
6 5
14
82k
7 6
9
IC1
555
11
13
~
~
10 +
~
D17
1N914
16VW+
+9V
D21
1N4007
+12V
100 +
2200
16VW+
LED7-8
GREEN
LED9·10
YELLOW
1500
~
B
ROC
VIEWED FROM
BELOW
~ Jt
100k
100k
~
~
~
~
~
I G0
TRAFFIC LIGHT SIMULATOR
Fig.4: the Traffic Light Simulator uses 555 timer IC1 to clock
decade counter IC2. This device then drives the traffic light
LEDs via transistors Q1-Q6 & a number of OR gates formed
by diodes D1-D20. Fig.5 (right) shows how the parts are
installed on the PC board. Each output driv~s tw,p LEDs of
the same colour, one for each opposing set of lights.
HIGH12J
(via an OR gate consisting ofD11-D16) and this turns on
the two red LEDs for the other set of lights.
The other diode OR gates ensure that the remaining
LEDs for each set of lights turn on and turn off in the
correct sequence as the 4017 counts up. For example,
when pin 7 is high, Q2 and Q4 are on and this lights
LEDs 3-4 (yellow) and LEDs 7-8 (red) . As with real traffic
lights, there is a brief period of time when both sets of
lights are red (ie, pin 10 or pin 11 high).
Each complete cycle takes about 25 seconds and is
then repeated. The timing period can be altered by
.changing the timing components in the oscillator (ICl) .
Power for the circuit can come from any +12V DC
source and this is applied to REGl to derive a regulated
+9V rail. Diode D21 protects the circuit against reverse
supply polarity.
Finally, a lOµF capacitor and 4. 7kn resistor are used
FEBRUARY
1993
29
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30
SILICON CHIP
This is the finished Traffic Light Simulator board. Take care with component
orientation & note that diode D21 is a 1N4007 type. The remaining diodes are
all 1N914 types & are installed with their cathodes towards transistors Q1-Q6.
to provide a power-on reset signal for
ICZ. This is necessary to ensure that
the 4017 starts reliably each time
power is applied to the circuit.
capacitor's charge is dumped via DZ
into one of the two solenoids that are
used to control the points (one to open
them and one to close them). During
Construction
Fig.5 shows the PC board parts layout for the traffic light simulator. You
can install the parts in any order but
take care with component orientation.
The outputs that drive the LEDs are
all marked on the PC board. Note that
each output drives two LEDs of the
same colour, one for each opposing
set of lights. The LED anodes are all
connected together and wired to the
+9V output on the PC board.
3. Points Controller
The final circuit is the Points Controller - see Fig.6. It can be powered
from any 12-15V AC or DC source. Dl
half-wave rectifies the incoming voltage in the case of an AC supply, or
provides reverse polarity protection
in the case of a DC supply.
When power is applied, Ql conducts and quickly charges the 2200µF
capacitor. At the same time, LED 1
lights to indicate that the circuit is
ready. The points can now be opened
or closed by pushing one of momentary-contact pushbutton switches (either S1 or S2).
As soon as S1 or S2 is pushed, the
There is room on the Points Controller
PC board for a second 2200µF
discharge capacitor, should this prove
necessary to operate the solenoids.
POINTS CONTROLLER
PARTS LIST
1 PC board, 54 x 36mm
1 TIP41 C NPN transistor (01)
3 1N4007 silicon diodes
1 red LED (LED1)
1 2200µF PC electrolytic
1 2.2kQ 0.25W resistor
1 3900 0.25W resistor
Why pay $1000's
for
encyclopedias?
If you own a computer with a CD drive,
then you can own the 22 vol NEW 1991
Grolier Electronic Encyclopedia for
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scanning!
LQQK
PARENTS
SQNy;
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Requirements
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OR
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Drive.
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PARENTS
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FAMILY.
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ENCYCLOPEDIA
'
•
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Translates to and from Chinese, Danish, English,
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Norwegian, Spanish & Swedish. Translations can
be exported directly to WP packages (Chinese
and Japanese display only). Includes the full text
of 18 dictionaries in 12 languages. - equivalent
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COMPUTER REQUIREMENTS (for package)
XT/AT Compatible, 512k Ram. DOS 3.1
Hard disc drive - half size slot
Recommended:
VGA Monitor & VGA adapter
Mouse
* Requires VGA
TITLE
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An interactive game designed to stimulate your
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•
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•
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340ms avg. access time
150KB sustained data transfer rate
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Output jacks for stereo and head phones
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See ue II Booth 141, HOME COMPUTER SHOW, Melbourne
I
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.J
D1
1N4007
12-15V
AC OR
DC
Q1
TIP41C
Fig.6 (left): the Points Controller uses the discharge qirrent from a
2200µF capacitor to control the points solenoids. This capacitor is
charged via Ql when power is applied. The capacitor discharges
& Ql turns off each time one of the pushbutton switches is press_
e d.
Fig.7 (below) shows the parts layout on the PC board.
~ J
---------e--o
BCE
$1
E
D2
1N4007
~
TO POINTS
SOLENOIDS
----------e--o
+
GND
12-15V AC
OR DC
+V TO 51
AND 52
GND
2200
25VW_
LED1
GNDo-------------t------oGND
POINTS CONTROLLER
this time, DZ also pulls Ql's base below its emitter and so Ql is turned
off. This ensures that the points solenoid only receives a brief current pulse
from the charged capacitor and prevents it from burning out if the button
is held down for too long.
The ZZ00µF capacitor charges via
Dl and Ql again as soon as the pushbutton switch is released. D3 protects
Ql against any large negative-going
spikes that are generated when the
solenoid turns on.
By the way, you can use this circuit
to control as many sets of points as
you wish - just wire in additional
m,omentary contact pushbutton switches to control their solenoids.
Construction
Assemble the parts on the PC board
as shown in Fig. 7, making sure that
Where to buy the kits
Kits for these projects are available from T. A. Mowles, PO Box 491, Noarlunga
Centre, South Australia, 5168; or from Force Electronics stores in Adelaide,
South Australia. The prices are as follows:
(1 ). Train Controller (does not include heatsink or TO-3 mounting kit) .. $27.95
(2). Traffic Light Simulator (includes 12 miniature LEDs) ..... .......... ....... $22.95
(3). Points Controller (does not include switches) ..... .. ....... ....... .. ..... ....... $9.95
Payment should be made by cheque or money order. Please add $3.50 for p&p
or $5 for 2-5 kits.
Note: copyright of the PC board patterns is retained by T. A. Mowles.
all polarised parts are correctly oriented. Note that some points solenoids may require more current than
can be delivered from a single ZZ00µF
capacitor. For this reason, there's space
on the board for a second capacitor if
required.
No heatsink is required for the
TIP41C since it only dissipates a few
milliwatts. If the LED brightness is
insufficient, reduce the value of the
series 2.ZkQ current limiting resistor.
In some cases, it may be necessary to
come down to 1.ZkQ.
SC
RESISTOR COLOUR CODES
No.
TRAIN CONTROLLER
0
0
0
0
1
1
1
Value
4-Band Code (5%)
5-Band Code (1%)
5.6kQ
470Q
0.22Q
green blue red gold
yellow violet brown gold
not applicable
green blue black brown brown
yellow violet black black brown
not applicable
100kQ
82kQ
4.7kQ
470Q
220Q
150Q
brown black yellow gold
grey red orange gold
yellow violet red gold
yellow violet brown gold
red red brown gold
brown green brown gold
brown black black orange brown
grey red black red brown
yellow violet black brown brown
yellow violet black black brown
red red black black brown
brown green black black brown
2.2kQ
390Q
red red red gold
orange white brown gold
red red black brown brown
orange white black black brown
TRAFFIC LIGHTS SIMULATOR
0
0
0
0
0
0
6
1
1
6
1
1
POINTS CONTROLLER
0
0
32
1
1
SILICON CHIP
|