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Remote controlled
gates for your home
Don’t you just love the idea of remotecontrolled gates? There is your stately
mansion, secure behind heavy wrought iron
gates. You roll up in your Lexus ES400 and
the gates slowly swing open as if by magic. As
you pass through, the gates swing shut again
and you are secure inside your domain.
By PHUNG MAI
Well, OK you might not have a
stately mansion nor a Lexus ES400 for
that matter but the idea of remote controlled gates is still pretty attractive,
isn’t it? Even if you just have ordinary
gates, someone, probably you, has to
open and close them each time you
pass through. That’s not too pleasant
on a cold, wet winter’s night. Now
66 Silicon Chip
you can add remote control.
Just think of the extra prestige automatic gates will add to your home.
It’s quite common for people to have
automatic garage doors but you can
go one better with automatic gates.
Of course, anyone can have automatic gates fitted to their home but
surprise, surprise, they cost big dol-
lars. The system presented here can
be obtained at a fraction of the cost
and you will end up with the added
satisfaction of building it yourself.
Mechanical concept
The basic mechanical parts required to motorise your gates are a
pair of 12V DC wiper motors from a
car and a pair of scissor jacks, again
from cars. You can pick these up very
cheaply from car wreckers. You can
buy them more cheaply at trash and
treasure sales because these people
think they’re selling junk! But you
know better. The wiper motors and
scissor jacks for the gates shown in
the accompanying photos cost just
$12.00. Cheap, huh?
Fig.1 shows the concept. The wiper
motor is attached to the moving gate
while one section of the scissor jack
is attached to the gate post. The wiper
Fig.1: this diagram shows the general concept for the motorised gates. The wiper
motor is attached to the moving gate while one section of the scissor jack is
attached to the gate post. The wiper motor drives the threaded shaft of the jack
to pull the gate open or shut. You need one wiper motor and one scissor jack
mechanism for each gate.
motor drives the threaded shaft of the
jack to pull the gate open or shut. You
need one wiper motor and one scissor
jack mechanism for each gate.
The photos illustrate the concept.
The prototype gates are in front of a
carport but the idea can be used anywhere, in inner-Sydney Paddington
or on a country property out the back
of Bourke.
Since DC motors are used to motorise the gates, it is a simple matter to
open or close them by changing the
current direction through the motors.
Beside the scissor jacks and automotive wiper motors alrea
dy mentioned, you will need a couple of
universal joints as found in standard
1/2-inch drive socket spanner sets and
a few pieces of steel and bolts to clamp
the jack sections to the gate posts. The
scissor jacks should ideally have a
1/ -inch shank to match the universal
2
joint – it will make your job a little
easier later.
Making the drive system
OK; you’ve got the wiper motors,
universal joints, jacks and some
steel. Despite the fact that the job
is involved with metals, it is not a
massive task. You will be impressed
when you see your little toy pushing
and pulling the gates. Fig.2 shows the
drive system in cross-section. The
steps you must follow are:
(1) Disassemble the universal joint.
(2) Centre punch into the universal
joint at the male end.
(3) Drill and tap the square shank
of the universal to fit the threaded
section of the motor shaft. These
steps will align the motor shaft to the
universal joint before they are welded
together.
(4) Disassemble the scissor jacks to
obtain the wanted parts. Use a hacksaw or an angle grinder to cut away
the unwanted sections.
(5) After you have removed the
threaded shafts from the jacks, you
need to make one end of the shaft
square to fit to the female end of the
universal joints.
As noted above, some jacks come
with a square drive so they are the
type to go for. Also make sure that
the screwed shaft has good “square
section” threads. Some jacks are very
flimsy and have a very shallow thread
ed portion; they should be avoided.
(6) Measure the depth of the female
end. Mark one side of the universal
joint at about half of the depth. Drill
at the marked point into the female
end through the shaft to fit a suitable
split pin.
(7) Reassemble the universal joint.
Drive system assembly
The next task is to assemble the various parts to make a workable drive.
One section of the jack is used to hold
the threaded bearing for the shaft to
wind through. This section is welded
August 1997 67
MOTOR SHAFT AND UNIVERSAL JOINT MALE SIDE
ARE WELDED TOGETHER AT DRILLED HOLE
SUPPORTER
MANUAL OVERRIDE
THROUGH FEMALE SIDE
WIPER
MOTOR
MOTOR SHAFT, THREADED SECTION
SQUARE END
THREADED SHAFT
THREADED BEARING
Fig.2: the drive system depends on universal joint to couple the wiper
motor to the threaded drive shaft.
to a clamp attached to the gate post.
The method of attachment is up to
you. You can either weld or drill holes
and fit bolts, depending on whether
you have wooden or metal gates.
The distance between the pole to
the threaded bearing is approximately
two-thirds the length of the threaded
shaft. You will have to allow for movement of the threaded bearing in the
supporter slot, to allow for the change
in the angle of the threaded shaft. The
steps are as follows:
(1) Thread the shaft into the tapped
hole in the universal drive shank and
then weld them together.
(2) Bolt the base of the motor to
the gate, as shown in the photos. The
distance between the position of the
motor on the gate to the hitch should
be approximately half the threaded
shaft length.
(3) Wind the shaft through the
threaded bearing about half of the
length, then open the gate toward the
shaft, place the shaft into the female
end of the universal joint and then fit
the split pin to connect them together.
PARTS LIST
1 single channel UHF
transmitter kit; available from
Oatley Electronics.
1 single channel UHF receiver
module (Oatley Electronics)
1 PC board, code 15108971,
122 x 99mm
4 SPDT 12V PC-mount relays
2 12V DC wiper motors
2 10A fuses
2 scissor jacks
1 universal joint and split pin
(see text)
Semiconductors
1 AX5328 decoder (IC5) (Oatley
Electronics)
2 74HC00 quad 2-input NAND
gates (IC1,IC2)
1 74HC20 dual 4-input NAND
gate (IC3)
1 74HC107 dual JK flipflop (IC4)
68 Silicon Chip
1 7805 5V regulator (IC6)
4 BC337 NPN transistors
(Q1,Q2,Q3,Q4)
5 1N4004 diodes
(D1,D2,D3,D4,D5)
1 1N914, 1N4148 small signal
diode (D6)
Capacitors
1 1000µF 16VW electrolytic
4 2.2µF 25VW electrolytic
1 1µF 25VW electrolytic
1 0.47µF metallised polyester
(greencap)
5 0.1µF monolithic
Resistors (0.25W, 5%)
4 2.2kΩ
2 1kΩ 5-pin resistor arrays (RN1,
RN2)
1 1kΩ
1 100Ω
Besides making the connection,
the split pin is a vital feature of the
system. If it ever jams or fails due to
loss of power or other cause, you will
always be able to open the gates by
removing the split pins.
(4) To test the gate, connect the
motor to a 12V car battery. Make the
motor run forward and reverse a few
times by changing the polarity, making sure that it is not jammed.
Normally a wiper motor requires
about 5A or so and you will have
two motors drawing this current. To
power them, you will need a 12V car
battery on permanent trickle charge,
say at around 100mA or so. By using
a car battery you will not be shut out
of your home if there is a blackout
and there is little chance of the circuit
ever locking up in the case of voltage
spikes on the mains supply.
Note that most wiper motors these
days have two-speed operation.
Choose the speed to give the smoothest operation of your gates.
Circuit details
The circuitry to control your gates
is built around the single channel
UHF remote control featured in the
February 1996 issue of SILICON CHIP.
This used an AX5326 encoder chip in
a keyring transmitter and an AX5328
decoder on a small PC board populated with surface mount components.
Both these items can be obtained from
Oatley Electronics – phone (02) 9584
3563 or fax (02) 9584 3561.
The AX5328 receiver board is
mounted on a large PC board with
a few logic chips and four relays to
control the two wiper motors. The
circuit of this board is shown in Fig.3.
While we show the circuit powered from a transformer with two
windings, the whole circuit can be
powered from a 12V car battery, as
noted above. To do this, delete the
transformer and the bridge rectifiers
and connect the battery to the points
marked +12V and VM+.
Note that the whole circuit could
also be operated without the UHF
remote control by pushbutton SW3.
You will need to refer to the February 1996 article for the details of the
UHF transmitter and receiver circuits.
When the transmitter button is press
ed, the output of IC5, the AX5328,
will go high.
In essence, the circuit consists of
two JK flipflops in IC4 and four RS
Fig.3: the circuit depends on a UHF receiver and decoder which drive several
RS flipflops based on IC1 and IC2. These in turn control four relays which
switch power to the motors to operate them in either one direction or the other.
flipflops based on NAND gate packages IC1 & IC2. All these flipflops are
reset when power is first applied.
IC4b is used to debounce push
button switch SW3. Assuming the cir
cuit has been power reset, all flipflops
will be cleared (ie, all Q outputs low)
with SW1 and SW2 opened (gates
closed).
If a valid signal is detected by decoder IC5, pin 17 will go high and this
is inverted by IC3a to trigger flipflop
IC4b. This makes flipflop IC4a toggle;
August 1997 69
from high to low and the RS flipflops
based on IC1c/1d and IC2b/2c will
be toggled via C11. Relays RLY2 and
RLY4 will operate and the gate motors
will be driven in the opposite direction until the flipflops are again reset
by the limit switches SW1 & SW2.
PC board assembly
Fig.4: the parts layout for the PC board. Take care to ensure all polarised
parts are installed correctly.
ie, its outputs change state, with Q
(pin 3) going high and pin 2 going low.
This causes the two RS flipflops
based on IC1a/1b & IC2a/2d to change
state after being toggled by IC4a’s
Q-bar signal via capacitor C12. As
a result relays RLY1 and RLY3 will
operate. Both motors now run until
the above RS flipflops are reset by the
limit switches SW1 and SW2. These
switches are installed on the gates
so they can reset the flipflops when
the gates are completely opened (or
closed).
With the flipflops reset, relays RLY1
and RLY3 are opened to stop the
motors. The output of 4-input NAND
IC3b gate also resets flipflop IC4b so
that it can accept another input signal
for closing the gates.
When the transmit button is pressed
again, pin 3 of IC4a will change state
You will need a wiper motor, a universal
joint and a threaded shaft from a scissor
jack to make each drive system.
70 Silicon Chip
In describing this project, we will
assume that you have the February
1996 issue and therefore will have
the construction information for the
UHF transmitter and receiver module.
The motor control part of the circuit,
as shown on Fig.3, is accommodated
on a PC board coded 15108971 and
measuring 122 x 99mm.
The component layout for the PC
board is shown in Fig.4. This has the
UHF receiver module mounted at one
end and the four relays at the other.
Check the board for any open
circuit tracks or undrilled holes and
fix any defects before inserting components. This done, fit all the wire
links and the PC stakes for external
connections. Next, fit the resistors,
the two resistor arrays and the diodes.
The next step is to fit the capacitors,
noting that the electrolytics must have
the correct polarity. The four transistors, the ICs and the relays can now
be installed.
Note that the UHF receiver module
should be left out until after the PC
board has been fully tested.
Testing
To test the unit, first connect a
20cm test wire to the edge GND pin
on the board. This wire will be used
to trigger or reset the flipflops being
tested. This done, connect 12V DC to
the AC input connector, then check
to see that +5V is present at pin 14 of
IC1, 2, 3 & 4 and pin 18 of IC5.
If all is OK so far then try grounding
the SW3 pin with the test wire. This
simulates a valid input signal being
received. Two of the relays should
operate. Assuming relays RLY1 and
RLY3 did, then reset them by grounding the SW1A and SW2A terminals.
This simulates the operation of the
limit switches.
Now ground the SW3 pin again
and relays RLY2 and RLY4 should
operate. Again, you can reset them by
grounding the SW1B and SW2B pins.
If the above steps didn’t work, then
you have to check the individual flipflops and you can check to see that the
The motor attaches to the gate and drives the shaft to pull
the gate open or closed. Note the split pin which enables
the universal joint to be uncoupled. We suggest that a
metal guard be fitted over each drive shaft to prevent the
possibility of accidental injury.
The wiper motors are weatherproofed by metal boxes
which give a tidy presentation (see photo on page 66). The
drive shafts will need to be kept well greased. A sliding
rubber boot inside a metal guard would provide good
protection for the shafts.
flipflop outputs are high or low with
your multimeter.
If the flipflops are all working correctly, you may have to check that
the transistors are all switching on
when they should and finally, that
there are no open circuits in the relay
connections.
Assuming that all checks are OK,
you can now install the UHF receiver
module on the PC board. Finally, test
the whole circuit once again with your
remote control.
Electrical installation
The control box should be located
near the battery and indoors or under
cover, to keep it out of the weather.
It is suggested that all cables be run
through plastic conduits and fuses
must be included, as shown on the
circuit. You will need flexible conduit
at the gates themselves. The cables
should be 4mm auto wire or thicker, to
avoid unwanted voltage drops when
the motors are running.
You have a number of choices when
it comes installing the limit switches
SW1 and SW2. Perhaps the easiest is
to use a pair of microswitches each
for SW1 and SW2 and have them
operated by the gates when they are
fully opened and fully closed.
When the whole circuit is wired
up, check the gate operation carefully
using the manual switch SW3 and
then the UHF remote control. Finally,
fit metal guards over each drive shaft
SC
to prevent accidental injury.
Fig.5: this is the full size etching pattern for the PC board.
PLEASE NOTE: although we have produced a PC board pattern for this
contributed design, the circuit has not actually been built or tested by Silicon
Chip Publications.
August 1997 71
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