This laser burglar alarm is built on the basis of a laser pointer. In armed mode, the beam from the laser pointer hits the photodiode. When a person or animal passes between the laser pointer and the photodiode, the beam is interrupted and the resistance of the photodiode increases dramatically.
The TL072 chip is configured as voltages. The reference voltage is formed by the divider on resistors R2 and R3 is fed to pin 3 of the D1 chip, and the compared voltage is fed to pin 2 from the divider R1 and VD1.
When the laser beam is interrupted, the voltage at pin 2 of the comparator drops lower than pin 3, causing pin 1 of the op amp to switch to the opposite state. This signal can control a siren, a computer, or some kind of executive device.
Laser burglar alarm - scheme
Resistor R4 is needed to prevent spontaneous switching when both inputs have the same voltage. Capacitor C1 prevents the device from being triggered by minor beam interruptions such as flying insects. If you want the signaling circuit to be more sensitive, then the capacitance of this capacitor can be reduced to 1 uF.
In past materials, we have considered many ways to manufacture various alarms, but have not yet talked about the manufacture of the most effective type of such security systems - laser. We are in a hurry to correct the error and present an overview of the video on the manufacture of homemade laser alarms.
What do we need:
- thyristor BT169;
- capacitor;
- resistors 47k;
- photoresistor or LDR;
- light;
- laser.
First of all, we present a laser signaling scheme, according to which we will assemble it on the Breadboard.
Let's start the assembly with a thyristor, which we connect to the breadboard. On the thyristor, the cathode is located on the left, the anode on the right, and the control electrode in the center. The diagram shows that the plus does not go directly to the thyristor, but necessarily passes through what we want to turn on. In this case, through an LED light bulb.
Therefore, the next step is to take a plus and feed it somewhere near the thyristor.
Then we feed this plus through the LED to the anode.
Let's look at the diagram. The cathode is immediately connected to negative. The cathode is on the left, so we connect the left leg of the thyristor to minus.
Also on the minus you need to connect a photoresistor and a capacitor. The author connects the capacitor to minus and to line 45 on the breadboard.
We connect the photoresistor to the minus and to the same line.
Now we connect a resistor to the same line, but from the plus.
Now these three need to be applied to the control electrode of the thyristor. To do this, we connect one wire contact to line 45, and wire the second to the central contact of the thyristor.
Let's test the alarm. To do this, turn on the laser and point it at the photoresistor. After turning on the power on the breadboard, you can see that the LED is off. It is necessary to slide a finger between the laser and the photoresistor, as the LED light bulb immediately lights up. After that, the alarm will turn off only when the power is turned off.
The alarm works according to the following principle. As soon as the light coming from the laser is blocked, the photoresistor activates the entire circuit. The thyristor, in turn, turns on the buzzer or LED, which we used in this case, and the alarm is triggered. Note that even when using the tweeter, you should not remove the LED bulb, because in this case the alarm will turn on when the object blocking the laser is removed, and the laser will begin to shine on the photoresistor.
The consumer market of security systems is full of various devices with which you can effectively protect property and prevent “uninvited guests” from entering your house, apartment or garage. Among the many security systems, a special place is given to laser alarm systems, which are difficult to hack and bypass. The presence of such devices guarantees a high level of security of the protected object, using the innovative capabilities of devices based on lasers. Such systems are quite complex, which is reflected in their cost, which is sometimes several times higher than conventional systems. But you should not refuse to install a laser security system if you do not have the required funds to purchase it. For any user who is at least a little versed in electronics, there is an alternative option - this is a do-it-yourself laser alarm. It turns out that using a few devices and components that are purchased for a symbolic cost, you can create an effective laser alarm.
Scope of laser signaling
Due to its high efficiency, laser signaling has a fairly wide practical application. It can be installed both indoors and around the perimeter of the protected object. This type of security complex is installed:
- in private houses and cottages;
- in apartments;
- in the offices of companies and enterprises;
- in banking institutions.
This type of alarm, given their high cost, must be installed at those facilities where valuables, jewelry or large financial resources are stored. In such cases, the use of laser security systems justifies itself and is cost-effective.
How does a laser alarm work?
The main elements of a security device are a source of laser radiation and a photodetector that receives this radiation. When a laser beam hits a sensitive photocell, its electrical resistance is several ohms. When the laser beam is interrupted, a sharp increase in the resistance of the photocell will occur, which through the relay leads to an impact on external actuators that provide an alarm.
Advantages
- the laser security system is highly mobile - its modules can be moved from place to place and located in different places;
- lasers can easily hide in a protected facility - thanks to this, the criminal may not even suspect that the alarm has gone off until the security department arrives;
- elements of the laser security system do not spoil the appearance of the object and easily fit into any interior;
- the alarm system can work with sound sirens, without them, with notification to the central console of the security company;
- do-it-yourself laser alarms can be quite simply created from improvised means.
Flaws
The disadvantages of this type of security system include:
- high price of the kit;
- complexity of installation and configuration.
Necessary components for DIY laser signaling
If you are thinking about how to make a laser alarm at home, then you should purchase several components with the help of which your own security system will be formed. For a simple laser signaling, you will need:
- laser pointer - will play the role of a laser beam generator;
- photocell - a device with replaceable resistance, which changes when exposed to a light flux;
- relay - it will be used to switch external actuators in the form of sound sirens, etc.;
- mounting accessories;
- body parts;
- switching conductors;
- tools and materials for soldering.
All of the listed parts can be purchased at any radio market and store, and some of them can be left at home as components from various household appliances.
A variant of a simple laser signaling scheme
Below is a laser pointer alarm, a circuit that can be built using a laser emitter and a NE555 timer that will control the operation of the alarm.
As a receiver-detector of the laser beam in this circuit, a photoresistor is used, which, when irradiated with a laser, has a small resistance, and when the beam disappears, its electrical resistance increases sharply. With an increase in resistance, the microcircuit provides the inclusion of an external device in the form of a sound siren.
Collection process
When creating a do-it-yourself laser alarm, the circuit can have an ordinary laser pointer or a children's toy laser as an emitter. Such emitters are powered by three small batteries, which are not enough for continuous operation. Therefore, the operating voltage for the laser should be supplied from a power supply of the appropriate rating. If this is not at hand, you can upgrade any low-voltage unit by adding a resistor to its circuit, which allows you to reduce the output voltage to the required value.
A three-pin relay system can be used as a relay, which provides turning off the laser and turning on the external siren. The relay can be purchased ready-made or you can make it yourself by remaking the relay assembly of some unnecessary device.
A wired communication line is connected to the relay contacts, which connects the sound siren with a photocell, which, when its resistance increases, ensures the relay is activated. In addition to the siren, the power line of the laser itself is also switched on through the relay. This is done so that when the alarm is triggered, when the laser beam was interrupted, it does not turn off again when the object blocking it does not leave the overlap zone. In this case, the siren will sound until the alarm is turned off using a special button.
Installation at home
Note!
Installation of a laser alarm at home should be carried out in those places that are most dangerous for penetration. For example, entrance doors or balcony doors - if the house is one-story or the apartment is located on the ground floor.
When installing, you should follow the rules that the laser signaling circuit must have the correct geometry. In this case, the security complex will work correctly and provide the required security.
The emitter of the laser beam and the photodetector must be located opposite each other on the same line so that the beam hits the center of the photocell. The light-sensitive element should be placed in a black tube to prevent it from being exposed to external light.
The button that enables / disables the alarm and the wiring to it should be located and laid hidden so that an attacker cannot turn it off on his own.
If a series of mirrors is placed between the emitter and the photodetector in a certain geometry, then you can get an excellent security device - a laser stretch of this type will allow you to cover a fairly large area. If the laser beam is interrupted anywhere, an alarm will be triggered.
Conclusion
The use of inexpensive elements that can be bought for a symbolic price allows you to create highly effective security systems that are able to respond to any movement in the protected area. Therefore, it is not always necessary to spend a lot of money in order to be able to use modern security technologies, it is better to think a little about how to make a laser alarm yourself and implement this task using improvised means.
Laser radiation has found wide application in professional security systems. But from the amateur radio point of logic, we are most interested in red laser pointers. Since the pointer has a low radiation power, it is safe for people and animals, however, laser radiation should not be directed directly into the eyes, as this can provoke a dangerous eye disease.
The principle of operation of laser signaling is as follows: when an object enters the beam coverage area, the laser stops illuminating the photodetector. The resistance of the latter increases sharply and the relay turns off. The relay contacts also turn off the laser. This is a variant of the simplest scheme.
When a laser beam hits a photoresistor, its resistance tends to zero, and when the laser is turned off, its resistance increases dramatically and greatly. The photoresistor must be placed in a closed case.
As a laser, a ready-made module with a red emitter from a cheap Chinese pointer is used. The laser head is connected to the power supply through a 5 ohm resistor. Active beam zone from 10 to 100 meters.
I propose for consideration a laser signaling circuit, the basis of which is a comparator based on an operational amplifier TL072. The reference voltage is formed by a voltage divider on the resistances R2 and R3 is fed to the third output of the TL072 chip, and the compared voltage is fed to the second output from the divider R1 and VD1.
At the moment of interruption of the laser beam, the voltage at the second output of the comparator decreases sharply, relative to the third output, as a result of which a signal appears at the output of the op-amp, which can control a siren or other actuator.
The resistance R4 is needed to protect against spontaneous operation, if the voltage at both inputs of the op-amp is equal. The capacitance C1 protects the operation of the device from a short interruption of the beam, for example from insects.
The body of the laser head must be opaque. It can be glued from black polystyrene. To avoid side illumination, it is recommended to glue a hood to the "window" of the photodiode. It can be made in the form of a "well" of square section from the same polystyrene. The photocell can be covered with a red light filter; it will slightly attenuate the laser radiation. To protect against strong electrical interference, the head is placed in a metal screen.
This scheme was described in detail in the radio magazine No. 7 for 2002, you can download and read the article by clicking on the green arrow.
This circuit works as a security system, and is a sensor for crossing a laser beam by an intruder. The circuit consists of two main parts: a photo relay (VT1, VT2) and a time relay (VT3, VT4).
If the laser beam hits the photoresistor, then the KV1 relay is turned off, and when the beam is interrupted, the relay will work, turn on the time relay with its contact KV1.1 and return to its initial state again. The time relay works according to the following algorithm. At the initial moment, when the KV1.1 contact is open, the voltage across the capacitor C1 tends to zero, and the transistors VT3 and VT4 are closed, the current does not pass through the KV2 relay winding and its contacts are open. When relay KV1 is triggered, capacitor C1 is charged and immediately starts to discharge through the emitter junction of the third transistor and resistance R8, while transistors VT3 and VT4 open, relay KV2 turns on and connects the actuator with its contacts. At the end of the capacitor discharge process, the circuit returns to its initial state. The resistance R6 can be used to adjust the time delay.
This light alarm circuit is activated when the light level of the sensor drops sharply, triggering an audible alarm. The device does not work with a smooth change in brightness. In order to increase the battery life, the audible alarm sounds from one to ten seconds, the sounding time can be adjusted using the R5 resistance.
It is desirable to use laser radiation as a light source, but in extreme cases, ordinary lighting is also suitable, but the circuit will work much worse. The sensitivity of the circuit can be changed by the resistance R1. The light sensor is a conventional photoresistor, the resistance of which is minimal when illuminated, and maximal when dimmed. Since the 555 timer chip has low power consumption, the standby signaling circuit consumes about 0.5mA.
This practically simplest option consists of two circuits: the radiation circuit and the beam reception circuit. The receiver circuit includes an electromagnetic relay for connecting an external alarm.
The laser emitter circuit consists of a red Laser LED with a wavelength of 650 nm and a power of 5 mW. LD1 is powered from a 5 V source. Two auxiliary elements are connected in series with it: a semiconductor diode D1 (1N4007) and a resistance R1 with a nominal value of 62 Ohms. LD1 can be borrowed from the Laser pointer.
The receiver circuit consists of a photoresistor that controls the relay using thyristor T1 (BT169). D2 (1N4007) protects the circuit from the back EMF pulse of the relay coil when thyristor T1 turns off.
An example of installing a laser stretch alarm is shown in the left corner of the figure above.
The scheme is also based on the idea with a red laser head from a laser pointer as a light source.
To eliminate the possibility of false operation, the circuit has a time delay. If it is necessary to increase it, it is necessary to add capacitance C1 or increase the value of variable resistances R2 and R3. Instead of the NE555 timer, you can take its domestic counterpart KR1006VI1. To prevent direct sunlight from entering the phototransistor, it is advisable to place it in a tube of a suitable diameter depending on the photocell body and at least 25 cm long. We cover the end with transparent glass to protect against various living creatures. The inner surface of the tube can be painted in a dark color.
Salute to all! If there have been robberies in your area more than once or there is such a danger, and you want to sleep peacefully at night, then you probably thought about the question: should I put an alarm on me ?.
But complex security systems are not always affordable, and you have to spend and spend money on installation and maintenance. True, there are cheap alarms, but intruders have long learned to turn them off, therefore, today I will show you how to make a simple and inexpensive laser burglar alarm yourself.
Laser signaling scheme
Since there are a lot of circuits today, I showed you what I think is the most current, using the very popular NE555 chip.
For assembly, we need the following components: piezo buzzer(which will beep), two resistors(750 Ohm, 130 kOhm), micro switch, photoresistor well, an integrated timer chip NE555.
A little about the NE555 timer
It was developed in 1972 by Signetics. It has a wide range of supply voltages: from 4.5 to 18 V, the output current reaches 200 mA, and the microcircuit itself does not consume much. The accuracy of the microcircuit does not depend on the supply voltage. There are a lot of elements inside the timer: about 20 transistors and many other details.
The microcircuit has eight legs:
- Earth
- launch
- Exit
- Reset
- Control
- Discharge
- Nutrition
It is important to remember that no more than 1/3 of the supply voltage must be applied to the second leg (start), and 2/3 of the supply voltage to the sixth leg (stop)!
Let's go back to our laser. The laser beam is directed to the photoresistor. When it is not irradiated, this leads to an increase in the voltage on the sixth leg of the microcircuit, as a result of which the buzzer turns on. You can turn off the speaker by pressing the microswitch. Watch a short video:
The choice of resistor R1 and R2 depends on the supply voltage. For example, I have a supply voltage of 4.5 V, so I chose resistors R1 - 130 kOhm, R2 - 750 Ohm. Since the laser batteries run out quickly, the laser can be connected to a more powerful power supply, usually 4.5 V.
With the help of several mirrors, you can cover the entire room with rays, the main thing is that the last mirror directs beam straight into the center of the resistor.
A laser alarm will always warn you when you are nearby, but you can also connect a more serious scheme: for example, with an SMS alert. If interested, let me know. That's all, sleep well, good dreams!
Sincerely, Edgar.