Alarms and Indicator Circuit: August 2011

Home Archives for August 2011

Asymmetric Timer

Description:
A timer circuit with independent mark and space periods.

Notes:
A simple astable timer made with the 555, the mark (on) and space (off) values may be set independently. The timing chain consists of resistors Ra, Rb and capacitor Ct. The capacitor, Ct charges via Ra which is in series with the 1N4148 diode. The discharge path is via Rb into into pin 7 of the IC. Both halves of the timing period can now be set independently.

The charge time (output high) is calculated by:

T(on) = 0.7 Ra Ct

The discharge time (output low) is calculated by:

T(off) = 0.7 Rb Ct

Please note that the formula for T(on) ignores the series resistance and forward voltage of the 1N4148 and is therefore approximate, but T(off) is not affected by D1 and is therefore precise.

Motorcycle Alarm No. 2

This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can immobilize the bike, flash the lights etc. Ron has used my Asymmetric Timer as the basis for his design.

Notes:
Any number of normally-open switches may be used. Fit "tilt" switches that close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc.

Once activated, the rate at which the siren switches on and off is controlled by R7, R8 & C4. For example, increasing R7 will make the sound period longer; while increasing R8 gives longer silent periods.

While at least one switch remains closed the siren will sound. About one minutes after all of the switches have been opened, the alarm will reset. How long it takes to switch off depends on the characteristics of the actual components used. You can adjust the time to suit your requirements by changing the value of R4 and/or C1.

The circuit is designed to use an electronic Siren drawing 300 to 400mA. It's not usually a good idea to use the bike's own Horn because it can be easily located and disconnected. However, if you choose to use the Horn, remember that the alarm relay is too small to carry the necessary current. Connect the coil of a suitably rated relay to the "Siren" output. This can then be used to sound the Horn, flash the lights etc.

The Support Material for this alarm includes a detailed guide to the construction of the circuit-board, a parts list, a complete circuit description and more. The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. The components are all drawn lying flat on the board - but those connected between close or adjacent tracks are mounted standing upright. The links are bare copper wire on the component side. Two of the links must be fitted before the IC. A more detailed guide to the board's construction and a circuit description are available on request.

Connect a 1-amp in-line fuse AS CLOSE AS POSSIBLE to your power source. This is VERY IMPORTANT. The fuse is there to protect the wiring - not the alarm. Exactly how the system is fitted will depend on the make of your particular machine - so I'm unable to provide any further help or advice in this regard.

You can use a key-switch or a hidden switch to set the alarm - or you could use the normally-closed contacts of a small relay. Wire the relay coil so that it's energized while the ignition is on. Then every time you turn the ignition off - the alarm will set itself. The quiescent (standby) current is virtually zero - so there is no drain on the battery.

Add an Automatic Immobilizer.

Before fitting this or any other immobilizer to your bike, carefully consider both the safety implications of its possible failure - and the legal consequences of installing a device that could cause an accident.

If you decide to proceed, you will need to use the highest standard of materials and workmanship. Remember that the relay MUST be large enough to handle the current required by your ignition system. Choose one specifically designed for automobiles - it will be protected against the elements and will give the best long-term reliability. You don't want it to let you down on a cold wet night - or worse still - in fast moving traffic!!! Please note that I am UNABLE to help any further with either the choice of a suitable relay - or with advice on its installation.

When you turn-off the ignition, the relay will de-energize and the first set of contacts (RLA1) will break the ignition circuit - automatically immobilizing the bike. The second set of contacts (RLA2) will turn-on the alarm.

When the ignition is switched on again the relay will not energize. The bike's ignition circuit will remain broken; and the alarm will continue to protect the machine. You must press Sw2 to energize the relay. It then latches itself on using the first set of contacts (RLA1). The same set of contacts completes the connection to the ignition circuit; while the second set of contacts (RLA2) opens and switches off the alarm.

The design has a number of advantages. It operates automatically when you turn-off the ignition - so there's no need to remember to activate it. The relay uses no current while the ignition is off - so there's no drain on the battery. To de-activate it you'll need to have the ignition key and you'll need to know the whereabouts of the push-switch. For extra security Sw2 could be key-operated.

Car Alarm and Immobilizer

Description:
This circuit features exit and entry delays, an instant alarm zone, an intermittent siren output and automatic reset. By adding external relays you can immobilize the vehicle and flash the lights.

Notes
The alarm is "set" by opening Sw1. It can be any small 1-amp single-pole change-over switch - but for added security you could use a key-switch. Once Sw1 is opened you have about 10 to 15 seconds to get out of the vehicle and close the door behind you. When you return and open the door the buzzer will sound. You have 10 to 15 seconds to move Sw1 to the "off" position. If you fail to do so, the siren will sound. The output to the siren is intermittent - it switches on and off. The speed at which it switches on and off is set by C6 and R10. While any trigger-switch remains closed, the siren will continue to sound. About 2 to 3 minutes after all of the switches have been opened, the circuit will reset.

One of the inputs is connected to the vehicle's existing door-switches. This provides the necessary exit and entry delays. It's usually sufficient to connect a SINGLE wire to just ONE of the door switches - they're generally all connected in parallel with the return through the chassis. You can add extra normally-open switches to the door-circuit if you wish; but note that any additional switches will have to be able to carry the current required by your vehicle's interior light.

Any number of normally-open switches may be connected - in parallel - to the "Instant" input. Since they don't have to carry the current for the interior light, you can use any type of switch you like. You may want an instant alarm on the bonnet, the boot, the rear-hatch, the rear-doors etc. It doesn't matter if these already have switches connected to the door-circuit. Simply fit a second switch and connect it to the instant input. It will override the delay circuit. You can use the chassis for the return. However, a ground terminal is provided if - for any reason - you need to run a separate return wire for either zone. If you're not using the instant zone then leave out Q2, R3, R4, R5 & D3.

The exit delay is set by R1 & C1, the entry delay by R9 & C4, and the reset time by R7 & C3. The precise length of any time period depends on the characteristics of the actual components used - especially the tolerance of the capacitors and the exact switching points of the Cmos Gates. However, for this type of application really accurate time periods are unnecessary.

The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. Fit a 1-amp in-line fuse AS CLOSE AS POSSIBLE to your power source. This is VERY IMPORTANT. The fuse is there to protect the wiring - not the alarm. Exactly how the system is fitted will depend on the make of your particular vehicle. Consequently, I CANNOT give any further advice on installation.

The circuit is designed to use an electronic Siren drawing 300 to 400mA. It's not usually a good idea to use the vehicle's own Horn because it can be easily located and disconnected. However, if you choose to use the Horn, remember that the alarm relay is too small to carry the necessary current. Connect the coil of a suitably rated relay to the "Siren" output. This can then be used to sound the Horn, flash the lights etc.

Add an Automatic Immobilizer.
Before fitting this immobilizer to your vehicle, carefully consider both the safety implications of its possible failure - and the legal consequences of installing a device that could cause an accident.

If YOU decide to proceed, you will need to use the highest standard of materials and workmanship. Remember that the relay MUST be large enough to handle the current required by your ignition system. Choose one specifically designed for automobiles - it will be protected against the elements and will give the best long-term reliability. You don't want it to let you down on a cold wet night - or worse still - in fast moving traffic!!! Please note that I am UNABLE to help any further with either the choice of a suitable relay - or with advice on its installation.

When you turn-off the ignition, the relay will de-energize and the second set of contacts (RLA2) will break the ignition circuit - automatically immobilizing the vehicle. When the ignition is switched on again the relay will not energize; and the vehicle's ignition circuit will remain broken. You must press Sw2 to energize the relay. It then latches itself on using the first set of contacts (RLA1); while the second set of contacts (RLA2) complete the connection to the ignition circuit.

The design has a number of advantages. It operates automatically when you turn the ignition off - so there's no need to remember to activate it. The relay uses no current while the ignition is off - so there's no drain on the battery. To de-activate it you'll need to have the ignition key and you'll need to know the whereabouts of the push-switch. Sw2 only requires a single wire because its return is through the chassis. It carries no load other than the current required by the relay-coil. So almost any small "momentary-action, push-to-make" switch will do. For extra security Sw2 could be key-operated.

Circuit Notes
Any number of normally open switches may be used. Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc. While at least one switch remains closed, the siren will sound. About two minutes after the switches have been opened again, the alarm will reset. How long it takes to switch off depends on the characteristics of the actual components used. But, up to a point, you can adjust the time to suit your requirements by changing the value of C1.

The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. Without its terminal blocks, the board is small. Ideally, you should try to find a siren with enough spare space inside to accommodate it. Fit a 1-amp in-line fuse close to the power source. This protects the wiring. Instead of using a key-switch you can use a hidden switch; or you could use the normally closed contacts of a small relay. Wire the relay coil so thttp://www.blogger.com/img/blank.gifhat it is energized while the ignition is on. Then every time you turn the ignition off, the alarm will set itself.

When it's not sounding, the circuit uses virtually no current. This should make it useful in other circumstances. For example, powered by dry batteries and with the relay and siren voltages to suit, it could be fitted inside a computer or anything else that's in danger of being picked up and carried away. The low standby current and automatic reset means that for this sort of application an external on/off switch may not be necessary.

The Support Material for this alarm includes a detailed guide to the construction of the circuit-board, a parts list, a complete circuit description and more.

5 Zone Alarm System

Description:
This is a complete alarm system with 5 independent zones suitable for a smalhttp://www.blogger.com/img/blank.gifl office or home environment. It uses just 3 CMOS IC's and features a timed entry / exit zone, 4 immediate zones and a phttp://www.blogger.com/img/blank.gifanic button. There are indicators for each zone a "system armed" indicator. The schematic is as follows:

Please Note: This diagram is drawn with Relay and Switch Contacts labeled as in Practical Section

Wheres the Parts List ? On the diagram click here for more info.

Circuit Notes
Each zone uses a normally closed contact. These can be micro switches or standard alarm contacts (usually reed switches). Suitable switches can be bought from alarm shops and concealed in door frames, or window ledges.

Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 - 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppressor. The key switch acts as the Set/Unset and Reset switch. For good security this should be the metal type with a key.

Operation
At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed. LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1. To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.

Gate Alarm

Description:
A cheap and simple gate alarm made from a single CMOS Integrated Circuit.

Circuit Notes
Figure 1 represents a cheap and simple Gate Alarm, that is intended to run off a small universal AC-DC power supply.
IC1a is a fast oscillator, and IC1b a slow oscillator, which are combined through IC1c to emit a high pip-pip-pip warning sound when a gate (or window, etc.) is opened. The circuit is intended not so much to sound like a siren or warning device, but rather to give the impression: "You have been noticed." R1 and D1 may be omitted, and the value of R2 perhaps reduced, to make the Gate Alarm sound more like a warning device. VR1 adjusts the frequency of the sound emitted.

IC1d is a timer which causes the Gate Alarm to emit some 20 to 30 further pips after the gate has been closed again, before it falls silent, as if to say: "I'm more clever than a simple on-off device." Piezo disk S1 may be replaced with a LED if desired, the LED being wired in series with a 1K resistor.

Figure 2 shows how an ordinary reed switch may be converted to close (a "normally closed" switch) when the gate is opened. A continuity tester makes the work easy. Note that many reed switches are delicate, and therefore wires which are soldered to the reed switch should not be flexed at all near the switch. Other types of switches, such as microswitches, may also be used.

Most of the power supply failure indicator circuits need a separate power supply for themselves. But the alarm circuit presented here needs no additional supply source. It employs an electrolytic capacitor to store adequate charge, to feed power to the alarm circuit which sounds an alarm for a reasonable duration when the supply fails.
This circuit can be used as an alarm for power supplies in the range of 5V to 15V.
To calibrate the circuit, first connect the power supply (5 to 15V) then vary the potentiometer VR1 until the buzzer goes from on to off.
Whenever the supply fails, resistor R2 pulls the base of transistor low and saturates it, turning the buzzer ON.

If there are any problems please contact webmaster@electronic-circuits-diagrams.com

This circuit utilising a 555 timer IC can be used as an alarm system to prevent the theft of your luggage, burglars breaking into your house etc. The alarms goes ON when a thin wire, usually as thin as a hair is broken.
The circuit is straightforward. It uses a 555 IC wired as an astable multivibrator to produce a tone of frequency of about 1kHz which gives out a shrill noise to scare away the burglar.
The wire used to set off the alarm can be made of a thin copper wire like SWG 36 or higher.
You can even use single strands of copper form a power cable.

The circuit operates on a wide range of voltages from 5V to 15V.
The speaker and the circuit could be housed inside a tin can with holes drilled on the speaker side for the sound to come out.

This circuit gives out an alarm when its sensor is wetted by water.
A 555 astable multivibrator is used here which gives a tone of about 1kHz upon detecting water.
The sensor when wetted by water completes the circuit and makes the 555 oscillate at about 1kHz.

The sensor is also shown in the circuit diagram.
It has to placed making an angle of about 30 - 45 degrees to the ground. This makes the rain water to flow through it to the ground and prevents the alarm from going on due to the stored water on the sensor.
The metal used to make the sensor has to be aluminium and not copper. This is because copper forms a blue oxide on its layer on prolonged exposure to moisture and has to be cleaned regularly.
The aluminium foils may be secured to the wooden / plastic board via epoxy adhesive or small screws.
The contact X and Y from the sensor may be obtained by small crocodile clips or you may use screws.

This very simple circuit just uses a couple of resistors, a capacitor and the easily available 555 timer IC.
The 555 is setup as an astable multivibrator operating at a frequency of about 1kHz that produces a shrill noise when switched on. The frequency can be changed by varying the 10K resistor.

This circuit not only indicates the amount of water present in the overhead tank but also gives an alarm when the tank is full.
The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs.
When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch low hence opening the switch and LEDs are OFF. As the water starts filling up, first the wire in the tank connected to S1 and the + supply are shorted by water. This closes the switch S1 and turns the LED1 ON. As the water continues to fill the tank, the LEDs2 , 3 and 4 light up gradually.
The no. of levels of indication can be increased to 8 if 2 CD4066 ICs are used in a similar fashion.

When the water is full, the base of the transistor BC148 is pulled high by the water and this saturates the transistor, turning the buzzer ON. The SPST switch has to be opened to turn the buzzer OFF.
Remember to turn the switch ON while pumping water otherwise the buzzer will not sound!

This tiny circuit comprising of a single 3 terminal IC UM66 can be built small enough to be placed inside a greeting card and operated off a single 3V flat button cell.
There is not much to the circuit. The UM66 is connected to its supply and its output fed to a transistor for amplification. You can either use a 4ohm speaker or a " flat" piezoelectric tweeter like the one found in alarm wrist watches.
If you use the piezo, then it can be connected directly between the output pin 1 and ground pin 3 without the transistor.
The UM66 looks like a transistor with 3 terminals. It is a complete miniature tone generator with a ROM of 64 notes, oscillator and a preamplifier. When it first came into market, it was programmed for the "Jingle bells" tune. Now they come with a wide variety of different tunes.