This is only a preview of the November 2004 issue of Silicon Chip. You can view 23 of the 112 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 "USB-Controlled Power Switch":
Items relevant to "A Charger For Deep-Cycle 12V Batteries, Pt.1":
Items relevant to "The Driveway Sentry":
Items relevant to "SMS Controller, Pt.2":
Items relevant to "Picaxe Infrared Remote Control":
Articles in this series:
Purchase a printed copy of this issue for $10.00. |
The
Driveway
Sentry
By JIM ROWE
Here’s a low cost, easy to build and install sensor
system for detecting moving vehicles like cars,
trucks, tractors or other farm machinery. It can also
be used to detect the opening and closing of metal
gates and roller doors.
U
nlike other sensing systems
that use light, heat or ultrasonic
sound waves to detect motion,
the Driveway Sentry operates by sensing small changes in the Earth’s magnetic field – the same magnetic field
that is sensed by a compass.
Since cars, trucks and similar vehicles contain a significant amount
of ferrous metal (iron, steel etc), they
inevitably produce small temporary
66 Silicon Chip
changes in the Earth’s magnetic field
when they move into or through an
area.
That’s how the Driveway Sentry
detects them, using a special high-sensitivity shielded remote sensor unit.
Because it doesn’t generate any
sensing fields of its own, the Driveway
Sensory produces no environmental pollution of any kind; it’s quite
‘clean’.
Also, because it only senses moving
iron and steel objects like vehicles,
it is much more selective than other
kinds of sensor.
This makes it immune to false
alarms from birds, dogs, cats, sheep,
cattle and other animals, falling tree
branches, rain and snow, people walking past and so on.
At the same time it can be used to
detect the movement of vehicles which
siliconchip.com.au
MAIN FEATURES
Exit Delay: Allows the system to be
switched to non-sensing ‘sleep mode’
for a period of about six minutes, to
allow the owner’s vehicle to exit from
the property without activating the
Driveway Sentry. At the end of the Exit
Delay period, the system returns to its
movement sensing mode.
Test Button: Allows the system to be
manually triggered into ‘movement detected’ alarm mode, without having to
drive a vehicle past the remote sensing
unit. This makes system adjustment
much easier and more convenient.
be disabled if you prefer the system to
respond silently.
onds and a maximum of about 25
seconds.
Relay Contacts: The Driveway Sentry
control box includes a DPDT relay
with two sets of changeover contacts.
These are activated when the system
detects movement, allowing the Sentry
to be connected to security systems,
telephone diallers, radio transmitters and so on. It can also be used to
control mains lighting, electric gates
or other equipment, via an external
mains-rated relay.
Probe Sensitivity Control: Allows the sensitivity of the Sentry’s remote sensing
unit to be adjusted over a wide range,
so it can be set for reliable vehicle (or
gate or door) movement detection without being too sensitive and susceptible
to false alarms.
Piezo Buzzer: Produces a high-pitched
sound to attract your attention when
movement is detected. This sound can
Alarm Duration Control: Allows the
duration of the system’s ‘movement
detected’ alarm mode to be adjusted
between a minimum of two sec-
contain very little ferrous metal – like
aluminium trailers, boats and caravans
- simply by attaching a strong magnet
to the underside of their frame. The
magnet ensures that if they’re moved
past the Driveway Sentry’s remote sensor unit, the Earth’s magnetic field will
be disturbed locally and the system
will activate.
The Driveway Sentry can also be
used to detect the opening or closing
of a ferrous metal gate, or a roller door
made from the same material, simply
by placing the remote sensor unit in
the appropriate position.
It can even be used to detect the
opening and closing of non-ferrous
(ie, timber or aluminium) gates or
roller doors, again simply by attaching a magnet to them. In short, the
Driveway Sentry has a multitude of
motion-sensing uses around the home,
farm or industrial facility.
By the way, the remote sensor unit
doesn’t have to be mounted directly
under the driveway or gateway, so
there’s no need to cut a trench in your
concrete drive. It’s sufficiently sensitive to detect moving vehicles within
a range of about 3-5 metres, so it will
work quite well when buried in a shallow trench alongside the driveway or
gateway.
The system operates from 12V DC
and draws very little current: less than
30mA when ‘armed’ and waiting, and
no more than 70mA when it senses
movement and is ‘alarmed’.
This means it’s very economical
and can easily be operated from a
12V battery and/or solar power, as an
alternative to an AC plugpack supply.
The Driveway Sentry has been developed by Jaycar Electronics, and as
a result the kit will only be available
from Jaycar.
Low Power Consumption: Operates from
12V DC power, with a low current drain
and power consumption – less than
70mA (0.84 watts), even in ‘movement
detected’ alarm mode. This means that
the system can be operated from a 12V
battery and/or solar power in rural and
other remote situations.
Because the project’s remote sensing unit uses a special construction
and involves many thousands of turns
of fine wire, this will be supplied
pre-built and sealed in a waterproof
housing with 30m of special shielded
cable attached. This should be sufficient to connect the sensor back to
the Driveway Sentry in most home or
business situations.
However if you need to monitor
vehicle movement much further away
from your house or office (say at a
remote entrance gate or machinery
shed), its alarm outputs can be connected back to your main security
system via a VHF or UHF radio link.
How it works
The heart of the Driveway Sentry is
its remote sensor, which as we said has
many thousands of turns of fine wire
wound on a long rod of ‘soft’ iron.
He’s the Sentry you don’t have to pay, feed or even be nice to . . . but he’s ready and rearing to go 24 hours a day! This
photo shows the control box and behind that, the sensor which is buried in the ground alongside your driveway.
siliconchip.com.au
November 2004 67
68 Silicon Chip
siliconchip.com.au
2004
SC
K
A
7
IC3c
IC3b
14
ZD1
16V
1W
A
K
1nF
10
4
C B E
PN100
10nF
11
RS
27k
12
13
11
10k
10k
330nF
9
CT
+1.4V
K
K
A
K
B
K
A
9
10
560Ω
16V ZENER
A
1N4004
A
1N4148
8
Vss
IC3a
3
+6V
1nF
1k
100nF
O13
3
2
1
+1.4V
BALANCE
VR1
1k 10T
33k
IC4 4060B
IC3d
100nF
68Ω
68Ω
10
RT
16
Vdd
MR
470k
12
IC3: 4011B
A
K
K
A
D1,D2: 1N4148
DRIVEWAY SENTRY
LEDS
100nF
8
S2
5
6
100k
9
D3
1N4148
A
K
EXIT
DELAY
100k
C1
G
C2
30m SCREENED
2-CORE CABLE
FARADAY
SHIELD
SENSOR
COIL
E
C
8
Q1
PN100
220k
2
7
6
220 µF
25V
5
3
100nF
8
A
LED1
POWER
K
D4
1N4004
1
IC2
7555
4
100nF
+3.0V
1k
220k
ALARM
DURATION
47 µF
25V
RBLL
47k
CON1
12V DC IN
VR3
500k
EXIT
DELAY
λ LED2
470nF
470k
IC1c
4
IC1: LM324
K
λ
A
1k
12
13
11
IC1d
470 µF
25V
IN
OUT
GND
E
C
A
B
+6V
E
C
7
TRIGGER
IC1b
100nF
RELAY1
100Ω
47 µF
16V
Q2
PN100
K
180k
5
6
68k
PIEZO
BUZZER
100Ω
Q3
PN100
–
+
REG1 7806
4.7k
+11.4V
B
TEST
S1
+4.4V
1k
PROBE
SENSITIVITY
D5
1N4004
10k
14
VR2 500k
LK1
BUZZER
ON/OFF
4.7k
470nF
+6V
OUT
GND
IN
7806
NO
COM
NC
NO
COM
NC
+11.4V
S2
EXIT DELAY
ZD1
C2
G
COM NC NO NO NC COM C1
NO
NC
POWER
100Ω
1k
PIEZO
BUZZER
+
16V
10k
68Ω
1nF
100nF
4148
D1
D2 4148
68Ω
1k
NO
REG1
7806
47 µF
a level where they are capable of being
applied to IC1b, which compares them
with a reference voltage of +4.4V from
the voltage divider formed by the 68kW
and 180kW resistors.
When the peak value of the amplified sensor signals exceeds the +4.4V
reference level, the output of comparator IC1b switches low.
This negative-going pulse is used to
trigger IC2, a 7555 timer IC configured
as a one-shot. The output of IC2 (pin 3)
then switches high, for a time period
set by the RC time constant connected
to pins 6 and 7. Trimpot VR3 allows
you to adjust this alarm duration time
between about two and 25 seconds.
When IC2 triggers on, it switches on
transistor Q3 and operates the relay.
The relay contacts can then be used
CON1
LED1
+
470 µF 25V
1N4004
COM
ALARM
TIME
33k
10k
Q2
PN100
100Ω
NC
COIL
LK1
100nF
MKT
100nF
NO
47k
100k
100nF
LED2
NC
RELAY1
4.7k
BUZ/NOBUZ
560Ω
Q1
PN100
Q3
PN100
D4
VR3
500k
EXIT DELAY
1k
470nF
1k
IC2
7555
4011B
10k
100nF
100nF
100k
4148
D3
100nF
27k
470k
+
47 µF
LL
+
330nF
IC3
100nF
VR1
PROBE
SENSITIVITY
10nF
MKT
IC4 4060B
IC1 LM324
D5 1N4004
NC
470k
220k
4.7k
1k
180k
68k
220k
4002 C
NO
1nF
100nF
220 µF
COM
This makes the coil very sensitive to
small changes in the Earth’s magnetic
field, of the type produced by a vehicle moving nearby. As a result of the
magnetic field changes, the coil generates tiny low frequency AC voltages,
and it’s these that are fed back to the
Control Box via twin shielded cable.
They are then amplified and used to
trigger the alarm circuit.
Because the sensor coil also tends to
pick up a significant amount of electrical noise and mains hum, it must be
fitted with a Faraday shield. This is a
thin sheet of metal foil encasing the
coil, providing it with an electrostatic
shield (without also forming a shorted
turn). The shield is connected back to
the Control Box ground via the cable
screening braid. The full circuit is
shown in Fig.1.
Inside the box, the small voltages induced in the sensor coil are amplified
by about 470 times in a DC amplifier
stage using IC1c – one section of an
LM324 quad op-amp.
Because of the high gain, this stage
is provided with fine manual control
over bias balancing, using 10-turn
trimpot VR1. Diodes D1 and D2, along
with zener diode ZD1 are used to
protect IC1c from blocking or damage
caused by induced voltage ‘spikes’.
The output from IC1c is further amplified by IC1d, configured as an AC
amplifier stage with gain adjustable
between about 5 and 500 times using
trimpot VR2.
This brings the peak amplitude of
the amplified sensor coil signals up to
siliconchip.com.au
470nF
YRTNES YAWEVIRD
VR2
500k
S1
TEST
100nF
+
Fig. 1 (left): the
complete circuit
diagram, and
Fig.2 (right):
the PC board
overlay. As you
can see, various
size piezo
buzzers can be
accommodated
on this board.
Note the
comments about
the relay in the
text: neither its
contacts nor the
PC board tracks
are rated to
handle 240VAC
– however, it
can be used
to switch an
external 240VAC
rated relay.
SENSOR COIL
CONNECTIONS
RELAY
CONTACTS A
RELAY
CONTACTS B
NOMINAL
12VDC
INPUT
to switch power to a siren, turn on
security lights or trigger your main
security system.
At the same time, the high level on
pin 3 of IC2 can be used to turn on
transistor Q2 which controls the small
piezo buzzer mounted in the Driveway
Sentry control box. If you don’t want
this internal buzzer to sound, it can
be disabled by moving link LK1 over
to the earthy side.
Note that pushbutton switch S1 can
be used to temporarily ground the
positive input of comparator IC1b.
This forces the output of IC1b low,
triggering IC2 in the same way as a
signal peak from IC1d.
So S1 provides a handy Test function, allowing you to do things like
adjust the alarm duration without
The completed PC board, as mounted in the jiffy box.
November 2004 69
Parts List – Driveway Sentry
1 PC board, code DRIVSENT, 133 x 83mm
1 Jiffy box, UB1 size (158 x 95 x 53mm)
1 Magnetic Sensor potted coil assembly (Jaycar)
1 12V DPDT relay, 5A contact rating
1 piezo buzzer
2 DPDT pushbutton switches (S1,S2)
3 3-way terminal blocks, PC-mounting
1 2.5mm concentric power connector, PC-mounting
1 3-pin SIL header strip, with jumper shunt
1 19mm square U-shaped heatsink
4 M3 tapped spacers, 25mm long
4 M3 machine screws, 9mm long countersunk head
5 M3 machine screws, 9mm long round head
1 M3 hex nut and star lockwasher
Semiconductors
1 LM324 quad op amp (IC1)
1 7555 CMOS timer (IC2)
1 4011B quad NAND gate (IC3)
1 4060B binary counter (IC4)
1 7806 +6V regulator (REG1)
3 PN100 NPN transistors (Q1,Q2,Q3)
1 16V 1W zener diode (ZD1)
1 5mm green LED (LED1)
1 5mm red LED (LED2)
3 1N4148 silicon diodes (D1,D2,D3)
2 1N4004 1A silicon diodes (D4,D5)
(SOIL)
REMOTE SENSOR
IN SHALLOW TRENCH
ALONGSIDE DRIVEWAY
1 68kW
2 4.7kW
WHERE TO GET THE KIT:
This project was designed and developed for Jaycar
Electronics, who own the copyright to the circuit, PC
board and illustrations.
A kit of parts will be available exclusively from all
Jaycar Electronics stores shortly after this issue goes
on sale.
The kit (KC5402) has all components listed above,
including the unique sensor coil and retails for $179.00
including GST.
Contact your nearest Jaycar Electronics store or visit
www.jaycar.com.au
70 Silicon Chip
SOIL USED TO
COVER SENSOR,
HIDING IT AND CABLE
DRIVEWAY
Capacitors
1 470mF 25V RB electrolytic
1 220mF 25V RB electrolytic
1 47mF 16V RB electrolytic
1 47mF 25V RBLL electrolytic
2 470nF MKT polyester
1 330nF greencap or MKT
8 100nF multilayer monolithic ceramic
2 100nF MKT
1 10nF MKT
2 1nF disc ceramic
Resistors (0.25W 1%)
2 470kW 2 220kW 1 180kW 2 100kW
1 47kW
1 33kW
1 27kW
3 10kW
4 1kW
1 560W
2 100W
2 68W
1 1kW trimpot, horizontal 10-turn (VR1)
2 500kW trimpots, horizontal (VR2,3)
The remote sensor, potted inside its PVC pipe protective
cover. Don’t try to remove it – the chances are very high that
you will damage or destroy it!
The drawing below shows how the sensor can be located in a
trench alongside the driveway – you don’t have to cut a hole
in the concrete to use the Driveway Sentry.
having to drive a vehicle near the remote sensor unit.
All of the remaining circuitry around IC3 and IC4 is
used to provide the Driveway Sentry’s ‘exit delay’ function. This operates quite simply by holding the reset pin
(pin 4) of IC2 low for a fixed period of about six minutes,
after power is first applied to the Driveway Sentry or after
pushbutton S2 is pressed at any later time. With its reset
pin held low, IC2 is prevented from triggering during that
time, allowing you to drive out in your own vehicle before
the Sentry is re-armed.
The exit delay circuit consists of a simple R-S flipflop using IC3b and IC3c, two of the gates in a 4011B quad NAND
gate. When power is first applied or when S2 is pressed,
the flipflop is switched into its reset state (pin 4 low), by
the temporary low on pin 8. This low is applied to the reset
pin (12) of IC4, a 4060B oscillator/14-stage binary divider
IC. IC4 is thus allowed to begin oscillating and counting.
This proceeds for around six minutes, after which IC4’s
pin 3 (output O13) finally drops to the low logic level. This
negative-going edge is coupled via the 10nF capacitor back
to pin 6 of IC3b, which switches the flipflop back into its set
state. In this state pin 4 goes high, holding IC4 in its reset
state and stopping its oscillator and counter.
At the same time, gates IC3d and IC3a (used as inverters)
apply a logic high to the reset pin of IC2, allowing it to be
triggered again. So the Driveway Sentry is re-armed.
Notice that during the exit delay time, there is a logic high
on pin 10 of IC3c, the lower flipflop gate. This is used to
turn on transistor Q1, which allows current to flow through
LED2. This LED is therefore only illuminated during the
exit delay period.
The power supply section of the Driveway Sentry is
straightforward. Diode D4 provides reverse polarity protection on the 12V DC input, while regulator REG1 provides
siliconchip.com.au
a stable +6V supply for all of the electronics apart from the relay. LED1 gives
indication that the Driveway Sentry
has +12V power and is operating.
Construction
Apart from the remote sensor unit,
all of the Driveway Sentry’s components and circuitry are mounted on a
small PC board measuring 133 x 83mm
and coded DRIVSENT. It is mounted in
a standard UB1 jiffy box measuring 158
x 95 x 55mm, which forms the control
box. The remote sensor unit connects
to it via the 30m shielded cable.
Since the remote sensor unit will be
supplied fully built up, you will only
have to wire up the control box - ie,
fit the components to the PC board.
This should be quite straightforward
if you use the PC board overlay diagram (Fig.2) and the internal photo
as a guide.
Begin assembly by fitting the two
wire links to the board. These are
near IC2 in the centre and they are
both 0.4” long (so you can use ‘0W’
dummy resistors if you prefer). Also fit
the three-way SIL header strip for LK1
at this time – it goes between IC2 and
the relay location. Then fit the three
3-way terminal blocks, which go on
the right-hand end of the board. The
2.5mm DC input socket can be fitted
as well, down in the lower right-hand
corner.
Now fit the resistors. Follow these
with the smaller unpolarised capacitors, then the larger unpolarised and
polarised capacitors. Make sure you
fit the latter with the correct orientation, as shown in the overlay diagram.
Note that there are two different
47mF electrolytics: one a low leakage
(RBLL) type, usually in a case with an
orange coloured sleeve, and the other
a standard RB type in a black sleeved
case. The low leakage unit goes near
IC2 in the centre of the board, while
the standard electro goes just to the
left of REG1.
Next mount the three trimpots, the
relay and the piezo buzzer. Note that
the PC board provides multiple holes
for the buzzer, to cope with different
buzzer pin spacings.
The two pushbutton switches can
be fitted after this, but you may need
to slightly enlarge the PC board holes
for these with a jeweller’s file, to allow
their lugs to pass through the board
sufficiently for soldering.
Begin fitting the semiconductors
siliconchip.com.au
The completed PC board mounted in
a UB1 Jiffy Box. Note the hole and
slot cut in the ends of the box – the
hole (right) is for the plugpack mains
adaptor, while the slot allows the
wiring from the sensor unit and
the wiring to external alarm/
controlled devices to enter
the box.
by adding the
various diodes, making sure you fit
them in the correct
locations and with the
correct polarity. Then fit the
three transistors, watching their
orientation also.
Follow these with REG1, which is
mounted horizontally with a 19mm
U-shaped heatsink. Its three leads are
bent downwards 6mm from the device
body and soldered underneath.
The regulator body is held firmly
down in contact with the heatsink
using a 9mm long M3 machine screw
with a star lockwasher and M3 nut.
The four DIL ICs are fitted next, making sure you fit each one the correct
way around as shown in the overlay
diagram.
As three of the ICs are CMOS, take
the usual precautions to minimise
the risk of electrostatic damage. Use
an earthed soldering iron, and ideally
earth yourself before picking up these
devices. Also solder their supply pins
to the PC board pads first, before soldering the other pins.
The final components to fit are the
two LEDs, which are both 5mm types.
The green LED fits in the LED1 position just below the relay, while the
red LED fits in the LED2 position just
above pushbutton S2.
Both mount vertically with the
lower surface of their body 20mm
above the board, so they will protrude
through matching holes in the box
front panel when it’s assembled. They
are also both orientated with their ‘flat’
side downwards, and their longer anode lead towards the top of the board.
Your Driveway Sentry board assembly should now be complete, and
ready for testing.
Testing and setup
For the initial testing, there’s no
need to connect the remote sensor unit
to the PC board assembly. Just connect
a 330W resistor temporarily between
terminals C1 and C2 at upper right on
the board, as a passive ‘stand in’.
Then connect a plugpack or another
source of 12V DC to CON1, the board’s
DC input connector at lower right.
If all is well, both LEDs should immediately light – LED1 because power
is present and LED2 because the exit
delay timing circuit has already begun
counting. LED2 should remain on for
about six minutes after power-up,
just as it should do after you press
button S2.
Next, connect a DMM to pin 8 of IC1,
and measure the voltage. It should be
between +2.5V and +3.0V. If it isn’t
inside this range, adjust trimpot VR1
until it is.
Now set trimpot VR3 to about midrange and check that link LK1 is in the
‘buzzer on’ position. Also wait until
LED2 is off, showing that the exit delay
circuit has timed out. Then press Test
button S1, which should make the
relay operate and the buzzer sound.
If the buzzer operating time is not
to your liking – ie, it’s too short or too
long – this can be changed quite easily
by adjusting trimpot VR3. The adjustNovember 2004 71
A couple of
keyhole slots cut
in the rear of the
Jiffy Box makes
it easy to mount
the box on a wall.
Naturally, these
need to be cut
before the PC
board is installed
in the box.
ment range is from about two seconds
up to about 25 seconds.
The only other adjustment to be
made to the Driveway Sentry is to vary
the sensitivity of the sensor probe. This
is done in much the same way as for
the alarm duration, but by adjusting
trimpot VR2. The adjustment must be
done later though, when the system
has been installed and the remote
sensor unit connected. For the present, simply set VR2 to its midrange
position.
Final assembly
The final step in building the
Driveway Sentry is to fit the PC board
assembly inside the main part of the
box. It mounts via four 25mm long M3
tapped spacers, using four 9mm long
M3 countersink head screws to fasten
the spacers in the box, and four 9mm
long M3 round head screws to attach
the PC board.
When the board is mounted inside
the box the pushbuttons will protrude
through matching holes in the front
panel, as will the two LEDs. The Probe
Sensitivity (VR2) and Alarm Duration
(VR3) trimpots can also be adjusted using a small screwdriver through their
labelled adjustment holes.
A 10mm diameter hole in the righthand end of the box allows the 12V
DC cable to enter, while an adjacent
rectangular slot allows entry of the
various sensor unit and relay contact
cables.
As you can see from the diagram
of Fig.3, the rear of the box has two
elongated holes to allow the completed
control unit to be mounted on a wall
using two 8G x 25mm self-tapping
screws or similar. The screws should
be fitted to the wall exactly 100mm
apart, in horizontal alignment and
72 Silicon Chip
screwed in with their heads only
2.5mm away from the wall.
Mount the control box in a position
where it’s unobtrusive, yet easy to access so you can press the Exit Delay
button before leaving.
Locating the sensor
The remote sensor unit is housed in
a sealed plastic tube 50mm in diameter
and 370mm long. It’s designed to be
placed in a shallow trench alongside
your driveway, so that it’s out of sight
while still being near any vehicles
moving on the driveway. If there’s
a steel-framed gate at the driveway
entrance, you can mount the remote
sensing unit under the area where the
gate is swung open, so it will detect the
gate being moved as well as a moving
vehicle.
Note that the remote sensing unit
doesn’t have to be mounted directly
under the driveway, because it’s quite
sensitive. So there’s no need to cut a
trench in your concrete drive – just
bury the sensor a small distance down
in a lawn or garden bed alongside the
drive.
The sensor is connected back to the
control unit via its attached 30m long
screened cable. The two inner wires of
the cable connect to terminals C1 and
C2, while the earthing screen connects
to the centre ‘G’ terminal.
There’s no need to dig a deep trench
for the probe. It only needs to be about
100mm below the surface, where it
should be hidden and protected from
damage. The cable can be run back to
the nearest building in a narrow trench
of about the same depth.
Sensitivity adjustment
Once the sensor unit has been fitted
in position and connected back to the
control unit, you’re ready to make the
final adjustment: probe sensitivity. As
explained earlier this can’t be done
using the Test button; it can only be
done using a vehicle moving along
the driveway, or someone opening or
closing the gate or roller door for you.
Trimpot VR2 is turned clockwise
to make the probe more sensitive, or
anticlockwise to make it less sensitive.
The best setting is where the probe
reliably detects the smallest moving
vehicle likely to enter or leave via the
driveway, without being more sensitive than this.
If you simply adjust VR2 for maximum sensitivity (ie, fully clockwise),
the Driveway Sentry may then be
prone to giving ‘false alarms’ due to
passing radio transmitters or mobile
phones, or during electrical storms.
Putting it to use
When the Driveway Sentry is
‘armed’ and detects movement, it immediately produces an alarm sound
from the buzzer and operates the relay.
The relay contacts can be connected to
another security system, so that when
the relay operates this can initiate further action like triggering a loud siren,
dialling a security firm, dialling your
own mobile phone or whatever action
you choose.
Please note that the relay contacts
in the Driveway Sentry control box
are NOT rated for switching 240V AC
mains power.
So if you want to have the Sentry
turn on high power floodlights or other
mains-operated equipment when it detects vehicle or gate movement, you’ll
need to do this via a second external
relay with mains-rated contacts (or a
mains-rated solid state relay).
The Driveway Sentry’s relay contacts can activate the external relay,
to control the mains-powered lighting or equipment. Jaycar can supply
a mains-rated solid state relay which
would be quite suitable for this: the
SY-4080, which can switch up to 3A
at 240V (ie, 720W).
The main external connection options for the Driveway Sentry are
illustrated in the diagram of Fig.3. As
you can see it’s very easy to hook the
Sentry up to a larger security system,
using a length of two-wire cable. One
wire connects to either COM terminal
on the control box, and the other wire
to either the NO (normally open) or
NC (normally closed) terminal in the
siliconchip.com.au
CONNECT
CORRESPONDING
CONTACT PAIRS
COM
NC
NO
COM
NC
NO
INPUTS
2
PHONE LINE
12VDC
NC
COM
NO
NO
COM
NC
1
TRIG
PHONE DIALLER
SECURITY
SYSTEM
DRIVEWAY
SENTRY
A
DRIVEWAY
SENTRY
CONNECTING TO A SECURITY SYSTEM
SOLID
STATE
RELAY
NO
NC
COM
B
CONNECTING TO A PHONE DIALLER
ESR2102400300
3–32 VDC
INPUT
4
– +
3
MAINS
PLUG &
CABLE
3A 240VAC
OUTPUT
2
1
ACTIVE
(BROWN)
WIRE
TO FLOODLIGHTS
OR SIREN, ETC
DRIVEWAY
SENTRY
0V
C CONNECTING TO A SOLID-STATE
RELAY FOR SWITCHING MAINSPOWERED LIGHTS, ETC.
EARTH (GRN/YELLOW) WIRE
+12V
NEUTRAL (BLUE) WIRE
INSULATE
THESE RELAY PINS
AND JOINTS
WITH HEATSHRINK
SLEEVING OR SIMILAR
EARTH
NEUTRAL
ACTIVE (BROWN) WIRE
ACTIVE
Fig. 3: connecting the Driveway Sentry to various external devices.
same group – depending on the security system input you
connect it to at the other end.
If the security system input expects NO contacts, connect
to the NO terminal; if it expects NC contacts, connect to the
NC terminal.
Connecting the Sentry up to a phone dialler is just as
easy. Again you simply use a two-wire cable, connecting
it to a COM terminal and either of the matching NO or NC
terminals depending on the type of contact action needed
to trigger the dialler.
When you want to connect the Driveway Sentry so it
can switch on external floodlights or a high-power siren
powered by the mains, this can be done by connecting one
of the Sentry’s relay contact sets so that it can operate an
SY-4080 solid state relay, or some other relay rated to switch
240V power.
As you can see, the positive input (control) terminal of
the solid state relay is connected to the +12V supply, while
its negative input is connected to the NO terminal of the
Sentry contacts.
The COM terminal of the same set of contacts is then
connected to 0V, so the solid state relay will be operated
(turned on) when the Driveway Sentry detects a moving
vehicle or gate.
The solid state relay’s output connections are then used
to switch 240V power to your siren or floodlights, etc. SC
siliconchip.com.au
8G x 25mm
SCREWS
(WALL)
1
OFFER LARGE ENDS OF
HOLES IN BOX REAR UP
TO SCREWS, THEN SLIDE
BOX DOWN TO FASTEN IT
2
DRIVEWAY SENTRY
CONTROL BOX
FRONT
PANEL
Fig.4: mounting the Driveway Sentry on a wall.
November 2004 73
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