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Design by JEFF MONEGAL
Get some real grunt with this . . .
10A DCC booster
for model railways
Most DCC base stations have puny current capabilities which are
exposed if you want to run more than a few locos and peripherals
on your model railway layout. Problem is, DCC boosters are
expensive, with a well-known 5A booster costing over $200.
Problem no longer; build this 10A beauty at a fraction of the cost.
I
F YOU ARE a model railway enthusiast you probably already know
about the current trends in model
railways, with Digital Command Control or DCC being the standard control
system of today. A beginner’s guide to
the DCC standard was published in the
February 2012 issue of SILICON CHIP.
64 Silicon Chip
The advantage of DCC is that many
model trains can be run on the same
layout at the same time and all under
individual control. In fact, many of
the DCC systems available today can
control or address up to 9999 trains
and peripherals at the same time.
Apart from being able to address
so many locos and peripherals, DCC
greatly simplifies the wiring to model
railways. There is no need to have
umpteen hundreds of wires going to
points, lights, track blocks etc. Since
the whole system can be regarded as a
serial bus (much like Ethernet or USB),
you need only connect a pair of wires
siliconchip.com.au
to every device and the individuallyaddressable DCC decoders take care
of everything.
Given that a DCC system can handle
such a huge number of model locomotives and other equipment, you
might wonder how much current a
typical system needs to deliver. The
current requirement for DCC locos
varies wildly. If the loco is large, with
a sound decoder and a smoke generator
(in the case of a steam loco), then the
current required may be 1A or more.
On the other hand, a small shunting
loco may require less than 200mA. All
of which makes it difficult to calculate
the current requirements of any layout.
To give an extreme example, on a
recent trip to a large model train layout
the author noticed that the layout used
a huge power supply. I asked the club
techo and he said it was an 18V DC
power supply capable of supplying
60A; that’s 1080 watts! The supply
was fitted with voltage and current
meters. At the time, the current meter
was showing the total layout load to
be 32A.
I was a bit shocked at this but was
informed that the DCC system was
siliconchip.com.au
running more than 25 locomotives, all
fitted with sound decoders and some
with smoke, right at that moment. At
the same time, it was powering a lot
of lighting with in excess of 80 lamps
and signal LEDs. As well, all the
point decoders were powered
from the DCC system.
Incidentally, he told me
that the power supply often
runs for hours at this level
yet uses only two small computer fans for cooling. That’s
what I call design efficiency!
But even if you’re not
running a large DCC layout
you will quickly find that you
run up against the limits of typical
DCC command (base) stations. Some
low-cost systems can only supply 1A
while the higher priced systems can
typically supply 3-4A.
The only way to get more current
capacity is to add a DCC booster. The
problem with most boosters is the
cost. A well-known brand of DCC
booster supplying 5A costs around
$200. Other boosters rated at only
3-4A cost well over the $100 mark. But
let’s be serious, if you want a booster,
you don’t want a flyweight; you want
a BOOSTER!
The booster presented here can supply up to 10A and you can build it for
a fraction of the cost of commercial
boosters. It has been tested on several
brands of DCC system and it operated
without any problems. It is fully compatible with NMRA (National Model
Railway Association) standards for
DCC systems and so should operate
with all systems that conform to the
NMRA standards. Incidentally, you
can view these standards and many
more on the NMRA web site: www.
nmra.org
As presented, our DCC booster is a
PCB module measuring 127 x 77mm.
It will need to be housed in a suitable case but it does not require any
heatsinks or fan cooling. It needs to
be teamed with a DC power supply
capable of delivering 16-18V and 10A.
The booster module has six LEDs to
indicate its status and a piezo beeper
which can sound a number of alarms
if fault conditions occur on the layout.
Circuit details
The full circuit is shown in Fig.1
and it does feature a PIC microcontroller but in this case the micro is
performing something of a cameo role
which we will detail later. The heart
of the circuit actually consists of four
IRF2804 Mosfets (Q3-Q6) which operate in bridge configuration to feed
the track on your DCC layout. Made
by International Rectifier, these are
specifically intended for automotive
applications and are rated for supply
rails up to 40V DC and 75A.
They are particularly suitable for
our booster design because they have a
very low on-resistance; RDS(on) is only
two milliohms (2mΩ)! That means that
their power loss when conducting at
10A is only 200mW each.
Other key devices in the circuit are
the 6N138 optocoupler (IC2) and the
two IR2110 high and low side Mosfet
drivers (IC5 & IC6).
The DCC signal from the base or
command station can be either the full
track voltage or the 5V signal typically
available from an RJ12 6-pin or other
modular connector. This connector
will have pins for +5V, 0V and the
DCC signal. Either source can be used
but they must be completely isolated
from the circuitry in the booster. This
is where the 6N138 optocoupler (IC2)
comes into the picture.
As shown, DCC track signals (if
used) are terminated to two pins on
CON2, each labelled “Track DCC”. One
“Track DCC” line is passed via a 1kΩ
resistor to pin 2 of the 6N138. This
is the anode of the internal LED. The
cathode of the LED at pin 3 connects
via the 3-way header socket to either
the other “Track DCC” line or to the
output (pin 1) of IC1a, one half of an
LM358 dual op amp.
Alternatively, if the 5V DCC signal is
used, this is buffered by IC1a which is
configured as a comparator. Note that
it uses the 5V supply from the base
station connector. LED6 is there to indicate if the DCC 5V supply is present.
The output of the 6N138 optocoupler drives a 74HC14 hex Schmitt
trigger inverter. All six inverters in
the package are used, firstly to buffer
the signal from the 6N138 (ie, by IC3a
& IC3f) and then to generate complementary (out-of-phase) signals to drive
the IR2110 high and low side drivers.
Dead-time is essential
Dead-time is essential to ensure
that each pair of Mosfets (ie, Q3 & Q4
or Q5 & Q6) are not both turned on at
any time. If that did happen, it would
effectively short the 16V supply rail
to ground and the result would range
July 2012 65
0.1 5W
+16-18V
+16 -18V
REG1 7805
0.1 5W
POWER
IN
IN
560
10 F
470nF
+5V
OUT
10 F
10 F
GND
LOW
ESR
LOW
ESR
LOW
ESR
1k
GND
560
CON1
E
1
4.7k
2
560
820
47k
A
FROM
CONTROLLER
560
8
A
A
K
RA2
RB6
RB0
RB1
RA4
9
K
K
LED1
LED2
LED3
LED4
LED5
POWER
DCC
OK
FAULT
V+ OK
OVER
LOAD
12
4.7k
B
Q2
BC548
E
3
17
OSC1
RB4
RB3
RA1
OSC2
RB5
5
K
10
CURRENT CONTROL
18
11
10 F
LOW
ESR
Vss
K
13
RA0
IC4
PIC16F628
16
RB2
15
A
RB7
C
10k
1k
TRACK
DCC
270
+5V
47k
330
3
IC1a
4
A
K
+5V OK
47k
10 F
LOW
ESR
A
K
D7
1N4148
IC1: LM358
8
2
1k
LED6
0V
7
RA5/MCLR
RA3
6
560
560
470nF
A
DCC
SIGNAL
(+5V)
Vdd
4
B
C
47k
14
560
Q1
C8550
PIEZO
BEEPER
K
1
D8
1N4148
6
5
IC1b
A DCC
7
A
SOURCE
SELECT
+5V
SIGNAL
TRACK
LK1
B
TRACK
DCC
CON2
SC
2012
10 AMP DCC BOOSTER
Fig.1: the DCC Booster circuit can be regarded as a high power buffer. It takes the 5V DCC or track DCC signals from a
command station and feeds exactly the same pulse signal to the layout tracks with a much higher current capacity of
up to 10A. And while it has a DC input of 16V (typical), it delivers a track signal of ±16V by virtue of its Mosfet bridge
output stage.
from increased dissipation through to
power supply malfunction and possibly even destruction of the Mosfets
themselves.
Dead-time is achieved as follows.
First, one signal path goes via diode
D1 in parallel with a 560Ω resistor and
bypassed by a 2.2nF capacitor before
driving IC3e. The diode means that
the positive edge goes through without
66 Silicon Chip
delay but the negative edge is delayed
by the RC filter. That means that the inverted pulse produced by IC3e has its
positive edge delayed but its negative
edge is not, resulting in a pulse which
is shorter than the output from IC3a/f.
IC3b and IC3c and a similar diode/
RC filter network are used to generate
a complementary (ie, out-of-phase)
pulse but in this case the resultant
pulse is slightly longer. The net result
is that these two pulses have “deadtime” whereby they are both at 0V each
time their polarity is swapped.
So far then, we have generated suitable complementary gate signals and
now we need to look at how these turn
on their respective Mosfets. Note that
the supply rail to the Mosfet bridge
circuit is between 16V & 18V but the
siliconchip.com.au
+16 -18V
+5V
10 F
10 F
LOW
ESR
10 F
A
D5
BA159
10
9
3
Vdd
Vcc
Hin
10 F
LOW
ESR
LOW
ESR
6
Q3
Q5
D IRF2804 IRF2804 D
470nF
22
5
Vs
9
Vdd
Hin
Vb
10
Hout
100k
(TO TRACK)
A
7
3
Vcc
S
CON3
100k
IC5
IR2110
470nF
22
G
G
S
SD
K
6
7
Hout
11
D6
BA159
K
Vb
LOW
ESR
A
5
B
IC6
IR2110
Vs
SD
11
CON4
D
12
Lout
Lin
Vss
22
1
S
COM
13
G
D
Q4
IRF2804
8
7
3
6
S
IC3d
8
470nF
13
5
1
14
IC3f
IC3a
1nF
IC3b
100k
470nF
IC3c
5
6
2.2nF
K
A
560
K
A
K
A
560
4
D1 1N4148
LEDS
13
2
A
K
A
7
CER
12
Vss
COM
D3
1N4148
D2 1N4148
3
Lin
K
12
2
Lout
D4 1N4148
1k
IC3: 74HC14
2.2k
1
100k
9
IC2 6N138
22
G
100k
2
+5V
2
Q6
IRF2804
11
IC3e
10
2.2nF
C8550
1N4148,
BA159
A
K
B
B
C
E
typical DCC signal fed to the tracks on
model railway layout has an amplitude
of around 30V to as much 44V peak-topeak. To obtain such a large signal we
need to drive the four Mosfet in bridge
mode whereby the 16V is alternately
connected in one direction and then
the other.
In practice, this done by turning on
Q3 & Q6 and then turning on Q5 & Q4.
siliconchip.com.au
BC548
E
G
C
In the first instance, Q3 connects one
side of the track (A) to +16V and Q6
connects the other side (B) to 0V. Then
Q5 & Q4 do the opposite, connecting
“A” to 0V and “B” to 16V. This happens at the DCC frequency of about
4.5kHz and the resultant track voltage
becomes 32V peak-to-peak.
Note that there is negligible voltage
loss across the Mosfets when they are
7805
IRF2804
D
D
S
GND
IN
GND
OUT
switched on, since their RDS(on) is so
low at 2mΩ.
The high and low-side drivers, IC5
& IC6, handle the gate signals to the
Mosfets. These ICs perform a number
of functions. First, they take the 5V
signals generated by IC3 and boost
them to 16V, equal to the Vcc rail at pin
3 of each device. Turning on the lower
Mosfets, Q4 & Q6, is pretty straightforJuly 2012 67
ward really; just feed in the requisite
positive 15V pulse signals which are
referred to the 0V line.
But driving Q3 & Q5 is a problem
because the gate pulse voltage must
be 15V above the respective source
electrodes, otherwise they would not
turn on. The IR2110s manage this by
using the switching action of the external Mosfets. For example, considering
IC6, Q5 & Q6, when Q6 is turned on,
the Vs line at pin 5 is pulled down to
0V and this causes the 470nF capacitor
between pins 5 & 6 to be charged to Vcc
via diode D6. Then, when Q6 is turned
off and Q5 is turned on, pin 5 is jacked
up to Vcc and it thereby pushes pin 6,
the top of the 470nF capacitor, above
Vcc by an amount equal to Vcc minus
the voltage drop across D6.
In other words, pin 6 of IC6 is now
pulled to almost 2Vcc or about 32V,
assuming at Vcc is 16V.
So Vb is the internal gate supply for
the high-side driver and IC6 connects
Vb to pin 7 and thence the gate of Q5,
each time Q5 is turned on. This a
classic case of “boot-strap” operation.
The final wrinkle in driving the
Mosfets involves feeding the gate signals from IC3’s inverter stages to IC5
& IC6. For example, IC3e drives pin 10
of IC6 (and thereby Mosfet Q5) as well
as pin 12 of IC5 (and thereby Mosfet
Q4). Similarly, IC3c drives pin 10 of
IC5 (and Mosfet Q3) as well as pin
12 of IC6 (and Mosfet Q6). This gives
the alternate switching of the Mosfets
referred to above.
68 Silicon Chip
LED4
V+ OK
OUTPUT 1
D6
BA159
D5
BA159
IRF2804
100k
100k
IRF2804
Q4
LED5
O/LOAD
Now we come to the microcontroller, IC4. It has a number of monitoring and control functions. The first
of these involves IC3d and the diode
pump involving D3 & D4. This generates a DC voltage while ever the DCC
signal is present. The “DCC present”
signal is fed to pin 11 of the micro.
If it is not present, IC4 pulls the SD
(shut-down) line to pin 11 on IC5 &
IC6 high, thereby removing any DCC
voltage from the tracks.
Secondly, the micro monitors the
incoming supply voltage from CON1
via a resistive divider. This divider is
connected across the main 16V rail
and its output fed to pin 18. The resistor values have been selected so that
if the DC supply drops below 10.8V,
the micro again shuts down IC5 & IC6.
Thirdly, the micro monitors the current drain, using PNP transistor Q1 to
sense the voltage across two parallel
0.1Ω 5W resistors. If the current drain
rises above 10A, the collector of Q1
goes high, pulling pin 2 of IC4 high.
Again, the micro responds by shutting
down IC5 & IC6. However, the story
is a little more involved at this point.
Momentary shorts across the track
do not cause the microcontroller to
shut off the gate switching signals
because the 470nF capacitors at the
emitter of Q1 and pin 2 of IC4 provide
a short delay. This means that momentary shorts which can occur in a DCC
layout when a locomotive crosses the
points in a reverse loop are ignored – a
very good feature.
OUTPUT 2
+
IC5 IR2110
MWJ
Fig.2: follow this parts layout
diagram to build the DCC
Booster. The LEDs can either
be mounted on the PCB or
on the front panel of the case
that’s used to house the unit.
10 F
Q3
22
560
LED3
FAULT
+
92 K
8K298
+
22
IRF2804
22
560
560
Q6
1102 YAM
LED2
DCC OK
100k
470nF
2.2nF
560
47k
LED1
ON
10 F
10 F
IC4 PIC16F628A
1nF
DCC
4kmBOOSTER
RETSOOBmk4
CCD
BEEPER
4.7k
10 F
10 F
470nF
+
100k
470nF
Q2
4148
22
IC6 IR2110
4148
D4
10k
47k
D1
4148
JWM
74HC14
560
+
1k
560
2.2k
DCC
SOURCE
D2
1k
BC548
+
SIG
IC2
6N138
4148
10 F
1k
820
4.7k
D9
LED6
TRK
47k
4148
0V
TRK
DCC
D8
DCC
SIG
IC1
LM358
+5V
10 F
470nF
IC3
1k
47k
270
330
TRK
DCC
560
KAL
2 x 0.1 /5W
FFEJ
IN PARALLEL
0V
IRF2804
Q5
+
560
+16+18V
470nF
+
C8550 470nF
10 F
100k
4148
D3
Q1
REG1
7805
10 F
2.2nF
C
560
YELTAO
SCINORTCELE
This view shows the completed
prototype. Note how the two
0.1Ω 5W resistors are installed
by mounting one on top of the
other.
Slightly longer duration shorts
cause the micro to pull its pin 10 high
and this shuts down IC5 & IC6. At
the same time it flashes the Fault and
Overload LEDs and causes the piezo
beeper to sound three times. The micro
then waits 4s and then pulls its pin 10
low, restoring DCC signals to the track.
However, it does this in a clever
way since DCC locomotives, especially
those with in-built sound decoders
present a difficult load at switch-on.
This is because all decoders, and particularly sound decoders, have large
electrolytic capacitors following the
bridge rectifier which is connected
across the DCC track supply.
Typically, this capacitor is 1000µF
or so but it can be 3300µF or more. So
you can imagine that a large layout
which might have 10 or more locomotives, with sound decoders, could easily have a total capacitance in excess of
35,000µF. When the DCC track signal
of 30V peak-to-peak is applied to the
track, the initial switch-on surge current can be very large, well in excess
of the 10A rating of this booster circuit.
So at switch-on and when restoring
power after a short-circuit, the micro
does not simply switch its pin 10
from high to low. Instead, it ramps it
down with a varying PWM signal over
a 1.5-second period, so that all those
decoder power supply capacitors are
charged at a manageable rate.
Furthermore, if a short-circuit con
dition is maintained, the microcontroll
er will cycle continuously between
siliconchip.com.au
Table 2: Capacitor Codes
Value
470nF
2.2nF
1nF
shut-down and then “having a look”
to see if the condition has been correct
ed. The result is that, in the face of a
permanent short-circuit, the Fault and
Overload LEDs will flash, the beeper
will sound three times and then it will
repeat after four seconds.
These loud beeps and the flashing
LEDs will leave you in no doubt that
a fault is present.
Q2 drives the PCB-mounted beeper.
As well as giving an audible warning
when overloads occur, it gives a couple
of quick beeps at switch on, as well –
just because we can.
As well as static tests to verify its
current rating and ability to handle
short-circuits, the booster has been
tested with DCC systems from various manufacturers. These included
Bachmann, Fleischmann, NCE, Lenz
µF Value IEC Code EIA Code
0.47µF
470n
474
.0022µF 2n2
222
0.001µF 1n
102
to its maximum you will need a DC
power supply capable of delivering
15-18V (preferably close to 16V) at
10A or more. The cheapest and most
compact approach will be to use a
switchmode open frame supply which
can be mounted in the same case as
the DCC Booster itself.
If you don’t need to run the booster
at maximum output and can manage
with, say, 7A or 8A, a laptop PC supply
delivering close to 16V will be ideal
for the job. Note that if you do use a
laptop power supply which inevitably
will not be able to supply the full 10A
(or more), you will need to change
the point at which the DCC Booster’s
overload circuit cuts in, otherwise
any overload on the model layout will
overload the power supply rather than
the DCC Booster.
So if your laptop supply is capable
of supplying 7A, we suggest reducing
the DCC Booster’s short-circuit current
to about 5.4A by increasing the two
parallel 0.1Ω 5W resistors to 0.22Ω
5W.
Alternatively, you could build a
large conventional power supply
with a 160VA (minimum) 12VAC
trans
former, a 35A bridge rectifier
and a minimum 20,000µF capacitor
bank rated at 25V. That will work but
will probably cost more and not be as
efficient as a switchmode DC supply
and you would need to be sure that its
and MRC Advance. All these systems
follow NMRA standards. When 10A
is being supplied to the track (using
a resistive load), the four Mosfets run
very slightly warm; no heatsinks are
required.
However, the two paralleled 0.1Ω
5W wirewound resistors do become
hot under these circumstances and if
you envisage running the DCC Booster
at close to is maximum rating for
protracted periods, you might want
to mount these two resistors off the
PCB, as will be discussed in a moment.
Of course, if you do envisage needing
such high currents for your DCC layout, that is an argument for building
two of these boosters.
Power supply requirements
If you want to run this DCC Booster
Table 1: Resistor Colour Codes
o
o
o
o
o
o
o
o
o
o
o
o
o
siliconchip.com.au
No.
5
4
1
2
1
4
1
9
1
1
4
2
Value
100kΩ
47kΩ
10kΩ
4.7kΩ
2.2kΩ
1kΩ
820Ω
560Ω
330Ω
270Ω
22Ω
0.1Ω 5W
4-Band Code (5%)
brown black yellow gold
yellow violet orange gold
brown black orange gold
yellow violet red gold
red red red gold
brown black red gold
grey red brown gold
green blue brown gold
orange orange brown gold
red violet brown gold
red red black gold
not applicable
5-Band Code (1%)
brown black black orange brown
yellow violet black red brown
brown black black red brown
yellow violet black brown brown
red red black brown brown
brown black black brown brown
grey red black black brown
green blue black black brown
orange orange black black brown
red violet black black brown
red red black gold brown
not applicable
July 2012 69
Parts List
1 PCB, code K298, 128 x 80mm
1 3-pin PCB-mount terminal block
1 2-pin PCB-mount terminal block
3 2-pin high-current PCB-mount
terminals (CON1,CON3, CON4)
2 8-pin IC sockets
3 14-pin IC sockets
1 18-pin IC socket
1 PCB-mount DC piezo beeper
1 3-pin header strip (LK1)
1 shorting link
Semiconductors
1 LM358 dual op amp (IC1)
1 6N138 optocoupler (IC2)
1 74HC14 hex inverter (IC3; do
not use 74C14)
1 PIC16F628A microcontroller
programmed with program
boost_mk4.asm (IC4)
2 IR2110 half-bridge Mosfet drivers (IC5, IC6)
1 C8550 PNP transistor (Q1)
1 BC548 NPN transistor (Q2)
4 IRF2804 Mosfets (Q3-Q6)
6 1N914, 1N4148 signal diodes
(D1-D4, D7-D8)
2 BA159 Schottky diodes
(D5, D6)
1 7805 regulator (REG1)
1 5mm yellow LED (LED1)
2 5mm green LEDs (LED2, LED4)
3 5mm red LEDs (LED3, LED5,
LED6)
Capacitors
9 10µF 50V low-ESR electrolytics
6 470nF MMC ceramic
2 2.2nF greencap or ceramic
1 1nF ceramic
Resistors (0.25W, 5%)
5 100kΩ
1 820Ω
4 47kΩ
9 560Ω
1 10kΩ
1 330Ω
2 4.7kΩ
1 270Ω
1 2.2kΩ
4 22Ω
4 1kΩ
2 0.1Ω 5W wirewound
DC output did not exceed 18V with
light loads.
Assembly
All the parts go on a double-sided
PCB (128 x 80mm) with platedthrough holes. The heavy currentcarrying tracks on the top and bottom
of the PCB are paralleled to increase
their current-carrying capacity.
70 Silicon Chip
Fig.3: this scope grab shows the output waveform from the DCC Booster which
had a DC input of 16V. Note that the long-term average value of DCC waveforms
is 0V. This waveform can only be measured if you have a floating power supply
(ie, not earthed) or an oscilloscope with differential inputs. Synchronising the
scope display with a DCC waveform is very difficult; this waveform is taken
with sweep stopped.
Fig.2 shows the parts layout on the
PCB. Assembly is a straightforward
process and you can start with the
small components such as the resistors and diodes. Make sure you check
each resistor using a digital multimeter
as you install it. The diodes must be
installed with the correct polarity. It’s
important that you install all components correctly the first time because
removing and re-installing them on
a PCB with plated-through holes is
not easy.
Having installed the resistors and
diodes, you can continue with the
other small components such as the
capacitors and the two transistors.
Again, make sure that you correctly
install the electrolytic capacitors and
transistors and make sure you don’t
inadvertently swap transistors Q1 &
Q2. The DC piezo beeper must also be
installed with correct polarity.
Mounting the 5W resistors
You need to decide whether you
want to mount the two paralleled 0.1Ω
5W resistors on the PCB or not, in view
of the fact that they will get quite hot
if you run the DCC Booster up to its
maximum 10A rating. If you decide to
mount them on the PCB, first piggy-
back and solder them together before
soldering the combination into the
PCB. The piggy-backed resistor must
be spaced off the PCB by about 4-5mm,
to improve ventilation and prevent
eventual discolouration (of the PCB).
Alternatively, if you are going to
run the DCC Booster at close to its
maximum ratings, use an aluminiumclad 0.05Ω 10W chassis-mount resistor such as this one from Element14:
http://au.element14.com/te-connectivity-cgs/ths10r05j/resistor-al-clad-10wr05-5/dp/1259281?Ntt=125-9281
Such resistors are not expensive
and by mounting them on the metal
chassis of the finished DCC Booster,
you can be sure that they will always
run reasonably cool.
With the sensor resistor wired in,
you can fit the PCB-mount screw
terminal connectors. Two types have
been specified: low current for CON2
and high current for CON1, CON3 &
CON4. The low-current connectors are
not critical but the high-current types
should be rated at 16A. As you can see
in the photos, they are substantially
taller than those used for CON2.
You can either mount the LEDs on
the PCB or, as we think most constructors will, mount them on the front
siliconchip.com.au
Where To Buy A Kit
A complete kit of parts is available from Oatley Electronics who own the copyright
for this kit. Cost of the kit is $70 plus $10 for postage & packing.
Fully constructed and tested units will be available on request. These units will
come with a 6-month warranty. Cost will be $100. Contact the project designer via
email for details.
Oatley Electronics can be contacted by email at sales<at>oatleyelectronics.com
Kits can also be ordered by phone on (02) 9584 3563 or by logging onto their web
site: www.oatleyelectronics.com
All technical enquires can be forwarded to the project designer at jeffmon<at>
optusnet.com.au All enquires will be answered but please allow up to 48 hours
for a response.
panel of the DCC Booster’s chassis or
case so that their indications can be
clearly seen.
The last components to be installed
are the four IRF2804 Mosfets. By the
way, don’t use substitutes for these
devices unless you know that their
RDS(on) values are at least as good as
those specified here.
Initial tests
At this stage leave the microcontroller (IC4) out of its socket. First,
connect a 16-18V DC supply to CON1.
You don’t need a heavy current supply
at this stage. Switch on the power and
check that 5V DC is between pins 8 &
5 of IC2, pins 14 & 7 of IC3 and pins
14 & 5 of the socket for IC4 (the microcontroller). This checks the function
of the 7805 5V regulator, REG1.
If all is OK, switch off and insert the
microcontroller into its socket. Make
sure the jumper link at LK1 is set to
position B, ie, to select track signals.
Note that no DCC signal should be
connected at this stage.
Switch on power and check that all
the LEDs come on for about 1s and
that the piezo beeps twice. The Fault
and DCC OK LEDs should then flash
and the piezo should also sound twice
every few seconds. If that happens,
then so far so good.
You can now connect a DCC signal
source (or a square-wave oscillator
set to 4kHz with an amplitude of
about 12V) to the “Track DCC” pins
on CON2. Now switch the power on
again. All LEDs should flash and after
a few seconds the “DCC OK” LED
should be steady and the Fault LED
should be off.
Now slowly wind the supply voltage
down to less than 11V. The Fault LED
and the “V+ OK” LEDs should then
flash alternately and the beeper should
siliconchip.com.au
give one beep every four seconds or so.
At the same time, the micro will have
shut down the Mosfet drivers, IC5 &
IC6. You can check this by measuring
the voltage at pin 10 of IC4; it should
be close to +5V.
If the DCC Booster has performed as
stated so far then it is a safe bet that
the it is working correctly.
Switch off and set the jumper link
to position B, ie, connecting a 5V DCC
signal. This can be supplied from the
5V connector on your DCC command
station or it can be a 5V 4kHz squarewave (DC-coupled) from a function
generator. Connect it to the appropriate
terminals on CON2 and you will also
need to connect a separate 5V supply
to power IC1.
Now the DCC Booster should perform as before. Of course, if you are
not going to use this facility, there is no
need to test it. In fact, you could omit
all the components associated with
IC1, including diode D1 and LED6.
Overload protection check
The overload protection can be
simulated using a small screwdriver to
short the collector and emitter leads of
Q1. The Fault LED and the Overload
LED should start flashing together
within half a second and the beeper
should give a series of beeps every few
seconds. Again, pin 10 of the micro
should go to +5V.
Finally, you can connect a high current supply set to around 16V DC and
run a fair-dinkum short circuit test by
using a clip lead to short the output
pins on CON3 or CON4. This time, you
will draw sparks, the Fault and Overload LEDs should start flashing and
the beeper will sound as before. Then,
when you remove the short-circuit,
normal operation will be restored.
That’s it – enjoy.
SC
Helping to put you in Control
Control Equipment
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A 4-20mA loop powered
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KTA-274 $99.00+GST
Pulse Stepper
Designed to provide
step and direction
signals to two stepper
motor drivers. Speed
is controlled by a single potentiometer
in the range 70 Hz to 4.8 kHz.
KTA-276 $39.95+GST
AC Current Transducer
These current transformers have a 4-20mA output. Available in ranges
of 0-30A or 0-50A they
are ideal for measuring motor currents
WES-005 $59.95+GST
Temperature Indicator.
The indicator comes with a
waterproof NTC sensor on
3m cable. The cable can
easily be extended to 50m. Indicators
available for thermocouples and RTD.
NOI-001 $69.00+GST
Enclosure with Prototype Board An aluminium enclosure with prototype board and 18 screw
terminals
ENC-032 $29.00+GST
Car Diagnostics Kit
Interface with your car's
OBD-II bus. Provides a
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ELM327 command set
and supports major OBDII standards such as CAN and JBUS.
SFK-003 $59.00+GST
Pressure Transmitter
A pressure transmitter with a
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with a ¼" NPT thread..
AXS-149 $149.00+GST
Contact Ocean Controls
Ph: 03 9782 5882
www.oceancontrols.com.au
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