Showing posts with label alarm. Show all posts
Showing posts with label alarm. Show all posts
Wednesday, September 11, 2013
Build a Auto Anti Hijack Alarm Circuit Diagram
This Auto Anti-Hijack Alarm Circuit Diagram was designed primarily for the situation where a hijacker forces the driver from the vehicle. If a door is opened while the ignition is switched on - the circuit will trip. After a few minutes delay - when the thief is at a safe distance - the Siren will sound.
Where it differs from the first two alarms - is in what happens next. Im obliged to Victor Montanez from the USA who suggested that the engine cut-out should not operate - until the vehicle comes to a stop. That way - the engine will not fail suddenly or unexpectedly. And the hijacker will retain control.
I havent been able to implement Victors excellent suggestion completely - because I couldnt think of a simple, reliable and universally applicable way of sensing when the vehicle has come to a stop.
Instead - I have postponed engine failure until the ignition is switched off. Once the thief turns off the ignition - the engine will not re-start. Clearly - there is no certainty as to when this will occur. But I think it will occur sooner rather than later. Because theres a strong possibility that the hijacker will turn off the ignition - in an attempt to silence the siren.
Auto Anti-Hijack Alarm Circuit Diagram
As well as acting as a Hijack Alarm - this circuit offers some added protection. Like the Enhanced Hijack Alarm - it incorporates Jeff Chias suggestion. That is - every time the ignition is switched on - the alarm will trip. So it will protect the vehicle whenever you leave it unattended with the ignition switched off - even overnight in your driveway.
Importance
Before fitting this or any other engine cut-out 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 standards of materials and workmanship.
Notes
Youre going to trip this alarm unintentionally. When you do - the LED will light and the Buzzer will give a short beep. The length of the beep is determined by C4. Its purpose is to alert you to the need to push the reset button. When you push the button - the LED will switch-off. Its purpose is to reassure you that the alarm has in fact reset.
If the reset button is not pressed then - about 3 minutes later - both the Siren and the Buzzer will sound continuously. The length of the delay is set by R8 & C5. For extra effect - fit a second siren inside the vehicle. With enough noise going on - you may feel that its unnecessary to fit the engine cut-out. In which case - you can leave out C7, D8, R12, R13, Ty1 & Ry2.
When the ignition is switched on - C3 & R4 are responsible for tripping the alarm. By taking pin 1 low momentarily - they simulate the opening of a door. If you dont want the alarm to trip every time you turn on the ignition - simply leave out C3 & R4.
Because the voltage on C3 may be reversed - the capacitor needs to be non-polarized. But connecting two regular 22uF capacitors back to back as shown - will work just as well. Because non-polarized capacitors are not widely available - the prototype was built using two polarized capacitors.
To reset the circuit you must - EITHER turn off the ignition - OR close all of the doors - before you press the reset button. While BOTH the ignition is on - AND a door remains open - the circuit will NOT reset.
The reset button carries virtually no current - so any small normally-open switch will do. Eric Vandel from Canada suggests using a reed-switch hidden behind (say) the dash - and operated by a magnet. I think this is an excellent idea. As Eric said in his email: - "... that should keep any thief guessing for a while."
Veroboard Layout
How you prevent the engine from starting is up to you. It should happen when Ry2 de-energizes. The contacts of Ry2 are too small to do the job themselves. So use them to switch the coil of a larger relay. Remember that the relay must be suitable for the current its required to carry. Choose one specifically designed for automobiles - it will be protected against the elements - and will give the best long-term reliability. You dont want it to let you down on a cold wet night - or worse still - in fast moving traffic!!! Remember also that you must fit a 1N4001 diode across YOUR relays coil - to prevent damage to the Cmos IC
YOUR relay should drop-out when Ry2 de-energizes. Wire YOUR relay so that when it drops-out the engine will not start. Because turning-off the ignition will cause both Ry2 and YOUR relay to de-energize - the standby current will be low - and the engine will be disabled while the vehicle is parked.
The circuit board 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 components on the circuit board. Please note that I am UNABLE to help any further with either the choice of a suitable relay - or with advice on installation.
Both the Siren and the Buzzer will go on sounding until the alarm is reset. The circuit is designed to use an electronic Siren drawing up to about 500mA. Its not usually a good idea to use the vehicles own Horn because it can be easily located and disconnected. However, if you choose to use the Horn, remember that Ry1 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.
Sunday, September 1, 2013
Alarm Indicator for High Temperature Reading
The circuit has been designed to provide an alarm with the use of a buzzer when sensing high temperature by using a thermistor.
These bipolar transistors form a Darlington pair to produce a very high current gain that is much higher then each transistor taken separately. This is made possible when the current amplified by the first transistor is further amplified by the second transistor. The overall gain is equal to the two individual gains multiplied together.A Darlington pair is designed in such a way that the collectors of both transistors are attached together and the emitter of the first transistor is directly coupled to the base of the second or output transistor. The base current of the output transistor is equal to the emitter current of the input transistor. When several transistors are used, it can form a cascade connection and the total current amplification factor will be very high since it is a product of current amplification factor of respective transistors.
Alarm Indicator for High Temperature Reading Schematic
When the Darlington pair conducts in this circuit, it causes the relay K1 to close thereby triggering the buzzer to produce sound due to the increase in temperature that is more than the predetermined value. The location of the thermistor should be far enough from other components of the circuit to prevent inhibiting their temperature. The circuit is powered by a 9 V battery for ease of transportation but a dedicated power supply can be provided is the circuit would be in a permanent location. A load, like a lamp or a LED, can also be connected to the contacts of the relay to produce a light indication or notification of the occurrence of excess temperature. Since the circuit is well insulated, the thermistor, connected to the circuit with a plated cable, can be submerged to water to cool down or reset the sensitivity and will not cause any short circuit. Doing this will regulate the trimmer.
This circuit can be designed not only by setting a detection of high temperature but can also be modified to be set on detection of low temperature in some industries. It can be used for refrigeration, walk-in freezer, or walk-in cooler systems and other environments that are sensitive in temperature. Some circuits incorporating high temperature alarm modules are being used in motor vehicles to detect the occupancy wherein the temperature element senses a highly dangerous temperature in the passenger compartment of a motor vehicle and energizes the occupancy sensor to determine the presence or absence of an occupant. In the absence of the occupant, the sensor de-energizes after a period of time while an audible alarm is triggered to create attention to the motor vehicle in the presence of an occupant. This type of alarm can be reset with the use of a key.
Having a temperature alarm can provide benefits like protecting valuable equipment due to high temperature, low temperature, or sometimes high humidity. Other high temperature program can be used to protect against air conditioning failure or against the heating system to turn off. On the contrary, low temperature program can be used against heating system failure by aiding to prevent frozen pipes. The alarm can also reduce downtime by receiving a telephone call and being notified of a possible power loss or failure before the damage occurs in an equipment.
The Darlington pair used in the circuit can also be used as an important component in a switching device while high power Darlington transistors can be used in emergency power supply and in control circuits for AC and DC motor control. These applications make the Darlington suitable for switching large currents in high power circuits.
- Thermistor – one type of resistor used as temperature-sensing element which demonstrates a large change in resistance proportional to a small change in temperature because of the composition of its semiconductor material.
- BC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment.
These bipolar transistors form a Darlington pair to produce a very high current gain that is much higher then each transistor taken separately. This is made possible when the current amplified by the first transistor is further amplified by the second transistor. The overall gain is equal to the two individual gains multiplied together.A Darlington pair is designed in such a way that the collectors of both transistors are attached together and the emitter of the first transistor is directly coupled to the base of the second or output transistor. The base current of the output transistor is equal to the emitter current of the input transistor. When several transistors are used, it can form a cascade connection and the total current amplification factor will be very high since it is a product of current amplification factor of respective transistors.
Alarm Indicator for High Temperature Reading Schematic
When the Darlington pair conducts in this circuit, it causes the relay K1 to close thereby triggering the buzzer to produce sound due to the increase in temperature that is more than the predetermined value. The location of the thermistor should be far enough from other components of the circuit to prevent inhibiting their temperature. The circuit is powered by a 9 V battery for ease of transportation but a dedicated power supply can be provided is the circuit would be in a permanent location. A load, like a lamp or a LED, can also be connected to the contacts of the relay to produce a light indication or notification of the occurrence of excess temperature. Since the circuit is well insulated, the thermistor, connected to the circuit with a plated cable, can be submerged to water to cool down or reset the sensitivity and will not cause any short circuit. Doing this will regulate the trimmer.
This circuit can be designed not only by setting a detection of high temperature but can also be modified to be set on detection of low temperature in some industries. It can be used for refrigeration, walk-in freezer, or walk-in cooler systems and other environments that are sensitive in temperature. Some circuits incorporating high temperature alarm modules are being used in motor vehicles to detect the occupancy wherein the temperature element senses a highly dangerous temperature in the passenger compartment of a motor vehicle and energizes the occupancy sensor to determine the presence or absence of an occupant. In the absence of the occupant, the sensor de-energizes after a period of time while an audible alarm is triggered to create attention to the motor vehicle in the presence of an occupant. This type of alarm can be reset with the use of a key.
Having a temperature alarm can provide benefits like protecting valuable equipment due to high temperature, low temperature, or sometimes high humidity. Other high temperature program can be used to protect against air conditioning failure or against the heating system to turn off. On the contrary, low temperature program can be used against heating system failure by aiding to prevent frozen pipes. The alarm can also reduce downtime by receiving a telephone call and being notified of a possible power loss or failure before the damage occurs in an equipment.
The Darlington pair used in the circuit can also be used as an important component in a switching device while high power Darlington transistors can be used in emergency power supply and in control circuits for AC and DC motor control. These applications make the Darlington suitable for switching large currents in high power circuits.
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