Home Chassis Presence relay for turning on the lights with your own hands. Motion sensors to turn on the lights. Model with magnetic photocell

Chassis

Presence relay for turning on the lights with your own hands. Motion sensors to turn on the lights. Model with magnetic photocell

Various types of detectors that allow monitoring of communications and security systems in buildings and private homes make it much easier to manage the entire complex as a whole. Due to built-in algorithms, devices operate autonomously, and human intervention becomes minimal. One of the important elements of such circuits are motion sensors. With the help of these devices you can protect the territory from unwanted intrusion and save on electricity. Sensors will automatically turn on and off lighting in the house and on the street, and switch power to other electrical appliances.

Most of these detectors can be made independently; the main thing is to understand the operating principle of these detectors. A DIY motion sensor can be a complex device or, conversely, be assembled from several parts.

Ring switch

The simplest motion sensors include self-return points (ring switches). Such equipment is used when turning on the light in the refrigerator. To operate the circuit, the following is used:

a reed switch or sealed contact is a flask with 2 ferromagnetic contacts sealed inside it;
magnet.

When the magnet approaches the reed switch, the contacts close, and when removed, they open. When the contacts are open, voltage is supplied to the lamp in the refrigerator, and the light comes on. When the contacts are closed, the light bulb is de-energized.

This homemade motion sensor can simply be connected to an existing security alarm or sound detector. Due to this, when the contacts open, that is, the door opens, the system will sound a sound signal. The scheme is used on the doors of protected objects, but is not suitable for open areas.

To control large areas, more complex devices are used that can respond to various changes in the environment. Such elements include:

photo, - and sound relays;
field sensors;
pyro receivers.

Light motion sensor

Quite often, a motion sensor is needed to detect an object as it moves across a certain line, for example, at the entrance to a room. To create such a sensor, two devices are needed: a light source and a photodetector. When a person passes in the area of the beams, the connection between the source and the receiver will be lost, the sensor will operate and produce a sound signal.

The entire circuit of this device is based on a photocell - a transistor. Moreover, such a phototransistor can also be made with your own hands. To do this, you need to take a transistor that looks like a hat with a brim on three legs, for example, P417A. You need to saw off the top of the element so that a hole is formed, or simply open the entire crystal. Now, when exposed to light, the element will begin to work like a phototransistor, although its sensitivity will be slightly less than usual. You don’t have to waste time on this operation, but immediately take a ready-made photocell.

First we assemble the photodetector. The device uses the following elements:

VT1 – phototransistor;
R1 – resistor;
C1 – capacitor;
DA1 – operational amplifier with feedback;
R2 – resistor with feedback to the operational amplifier;
R1 – performs the functions of load and collector. Using this element, the operating point is set. The selection of the required value is done empirically.

When choosing the characteristics of R2, it should be remembered that the higher the gain, the less stable the amplifier. On the other hand, the higher the resistor value, the greater the gain. It is optimal to use a nominal value of 100 kOhm.

Homemade products work as follows:

when light hits the transistor, a small operating voltage appears and the element opens;
the capacitor is charged;
if the light goes away, the capacitor begins to discharge;
at point A the voltage decreases, which reduces the voltage at the output;
An operational amplifier is needed to amplify the signal from point A for further transmission to other devices.

A photodiode can be used as a light source at short distances. The red laser will allow you to significantly gain distance. The laser motion sensor can be used over large areas. But if you need to make the sensor invisible, use an infrared diode.

Attention! When selecting a laser diode, check that its characteristics comply with safety regulations. Some of these elements have a detrimental effect on the eyes.

The photosensor itself must be darkened and covered with dark transmissive material. This will reduce the influence of conventional lighting. We place the light source opposite the sensor. Due to this, an optical connection is formed, that is, until the object covers the light source (crosses the line), the voltage in the phototransistor will be constant. When the optical connection is broken, the output voltage is reduced to zero by the operational amplifier.

To analyze the data coming from the sensor, a relay should be connected to the circuit. We connect the winding to the input, apply 12 V to 1 contact, ground the other end, and connect the third to the radio. If light falls on the photocell, the power circuit is connected to the photodetector, the radio does not work. If the optical link is broken, the voltage drops and the power supply is shorted to the radio. This causes the radio to turn on. Instead of a radio receiver, other detectors can be used.

Motion sensors with capacitive relay

The capacitive relay reacts to the occurrence of objects within a given radius. The main elements of such equipment are an antenna and a microwave generator.

Many of us have noticed that the sound of a radio changes when a person gets very close to it, strange noises appear in operation, or the station’s waveform gets lost. Microwave motion sensors operate on exactly the same principle.

The role of the high-frequency generator of the radio receiver in the circuit is simultaneously performed by transistor VT1. A detector diode is needed to rectify the voltage, which sets the bias at the base of transistor VT2. Transformer T1 has windings tuned to different frequencies. If the antenna is not affected by external objects, there is no voltage on the VD1 detector, since the signal amplitudes cancel each other. If the frequencies change, the amplitudes begin to add up and are detected on the diode. Due to this, VT2 opens. In order to accurately set the value for turning off and turning on, a comparator is used - thyristor VS1. This thyristor is controlled by a 12-volt power relay.

Important! Sensors should not be placed near fans or large household appliances. All this equipment can interfere with the operating mode of any sensor.

Design Platforms

To create more complex and functional devices, you can use ready-made boards for radio design, for example, Arduino. This is the name of a hardware computing platform with its own processor and memory. Arduino performs several important tasks at once:

reads and processes the signal from the infrared sensor;
reacts to movement;
carries out notification.

To create the sensor you will need the platform itself, a PIR sensor, a breadboard and wires. You can connect the sensor directly to the Arduino, but it is more difficult to ensure a tight fit. Therefore, it is more convenient to use a Bradboard.

All infrared sensors have the same structure. The main parameter by which one sensor can be distinguished from another is sensitivity, and, therefore, the optics used. The optimal PIR sensor today is a device with Fresnel lenses. These lenses can concentrate radiation, increasing the threshold of sensitivity.

The main task of the platform is to send data via USB Serial when motion is detected at certain intervals. Hardware debugging is carried out using Python and PySerial software.

Such a motion sensor for turning on the light can be programmed to create a certain level of illumination. This equipment can be used to set up an alarm system in the garage, then the detector will be connected to the sound module.

Video

This article is a continuation of the article about, which caused heated discussion and many questions. Well, since I receive a lot of questions about repairing motion sensors, I decided to include them in a separate continuation article.

The most important thing I want to convey is that the main thing is not to know how to solder and check the integrity of the elements. The main thing is to be able to think logically and critically, research, and analyze. And gain experience.

There are many motion sensor schemes, but the principle is the same. This principle and much more regarding this device is given in the link at the beginning of the article; once again I recommend studying it and the comments to it. The same article contains links to other articles about motion sensors, you can download instructions and datasheets for the details of the sensor's electrical circuit.

Typical motion sensor malfunctions

The motion sensor for turning on the light may have the following faults:

Doesn't turn on.
Doesn't turn off.
It turns on or off at the wrong time.

Below we will analyze these faults in detail.

Subscribe! It will be interesting.

Once again about the schemes

So, I will give the most popular motion sensor circuit again:

This diagram was sent by my regular reader Alexander from Korolev in December 2014, for which I thank him again. I will rely on this diagram throughout the text of the article, since it is the most typical. It should not be confusing that the circuit in our example will be scattered across two boards - low-current and power.

At the end of the article, a refinement of this scheme will be given.

Now I’m publishing photos of motion sensor boards sent by another reader of mine, Renat.

Low current motion sensor board

Motion sensor power board

Here is our correspondence with Renat:

Renat: Hello! According to the diagram and description, I have the same sensor, I don’t know the exact model, they asked me to look at it, “it stopped working.” I settled on the power board. I checked all the elements, after the diode bridge + 24V comes out, the zener diode outputs + 8V, unsoldered the second part of the circuit (the board with the IR receiver, microcircuit, etc.). And now, I can’t understand why the relay activates when I apply voltage?

Renat: Hello Alexander! An integral stabilizer is not worth it. I connected it, everything is still the same (the relay is activated, does not respond to the sensor, adjusting the sensor, time and “day”/”night” mode also does not change anything.

Renat did a lot of work with his own hands, and I will try to help him in this article.

Where to start repairs if the sensor does not work

These arguments and methods of mine apply not only to a specific motion sensor, but also to many electronic devices. For example, k, the circuit of which is much simpler, but the principle is the same.

1. Check that the connection is correct. At this stage, you also need to find out why the motion sensor does not work and under what circumstances. Options (brainstorming):

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leap of light,
turned off the electricity
construction work,
an electrician came to the neighbors,
some kind of smell
the children were spinning
hit
the dog chewed
neighbors flooded
there was wind yesterday
sometimes it didn't work well
etc.

At this stage, it is already possible to identify the direction in which to move further.

You need to check that the connection is correct, make sure that the sensor is receiving the correct power, and if there are indicators, they should be on. Some. Sometimes. Next, simulate a situation in which it should work.

2. Correct adjustments. The regulators may be installed incorrectly, and it is enough to adjust the sensor correctly. To do this, you need to put the controls in positions in which it is most likely to turn on: Set the illumination level to a position at which the sensor will operate both day and night. Set sensitivity to maximum. Set operating time to minimum. In any case, it’s worth turning the controls and analyzing how the sensor behaves and whether it reacts at all.

Opening the sensor

If after the first stage the sensor does not work, you need to get down to real work.

We open the sensor and look at the boards. The first thing you need to pay attention to is the integrity of the elements. In addition, the smell will tell a lot to a knowledgeable person. There should be no suspicious parts - darkened, cracked, swollen, loose.

The PCB tracks must be intact. Sometimes it happens that they crack or break near the ration points (nickels). And of course, if the track is burnt out, you need to restore it with a jumper and analyze the reason.

We carefully check the soldering. In case of the slightest suspicion, we shake the suspicious parts and solder these places. Often the input wires and wires between the boards are sealed off, as well as adjusting elements (variable resistors).

Test run

Connect power to the sensor. I recommend using an incandescent light bulb with a power of 25-60 W as a load to indicate the operation of the sensor. Otherwise, if you focus on the clicking of the relay, you may not hear or understand whether it is on or off. Now we check the relays and connections.

A better option is to connect through a transformer (with an output voltage of 220V) or a difavtomat, this will significantly reduce the risk of electric shock (we will work with open live parts!).

Another option is through a 60-100W incandescent light bulb, this will save you from a short circuit. But it's not convenient.

On the use of circuit breakers.

We check that the required supply voltage is present on the power board.

I won't tell you how to use measuring instruments or how to check parts. If you have questions, write in the comments.

In addition, I urge you to be careful and remember your safety! During repairs it may get fucked up!

Once again we return to where we started the repair (point 1). There is a high probability that after inspection, soldering, and replacement of visually faulty parts, everything will work.

Checking the power

In the motion sensor, the 220V input power is converted into DC voltage required to power the circuit. As a rule, these voltages are 8, 12, 15, 24 V in different combinations, depending on the circuit.

All voltages are measured relative to zero. The point where you can take a zero - for example, the minus of an electrolytic capacitor at the output of a diode bridge.

In this case, you first need to check the +24V voltage (see diagram at the beginning of the article). If it is not there, you need to check the limiting (quenching) elements in front of the diode bridge, and the diodes themselves.

It is possible that the subsequent circuit “extinguishes” or adds power. To verify this, you need to disconnect the subsequent circuit from the power supply circuit.

We also check the low voltage +8V, which is used to power the operational amplifier circuits.

If it is not there, we check the circuits before it (presence of +24V), the stabilization circuits (zener diode), and test disconnect the load.

Power circuits

We don’t delve into the intricacies of operational amplifiers yet; we continue to explore the most obvious and probable.

In this case, this is checking the operation of the power board relay. This relay turns on, that is, a 24V voltage is supplied to its coil, if the key transistor opens. In this case S9013, n-p-n.

It is better to check with the low-current board completely disconnected. We just turned it off when checking the power supply in step 4.

To check the operation of a transistor, its base must be connected to the emitter, preferably through a resistor. It is there (R21, 20 kOhm), or use your own, about 2 kOhm - 33 kOhm. The transistor in this case will be closed (no current flows through it), and the relay should be turned off.

Next, we check the opening of the transistor and, accordingly, the activation of the relay. To do this, through the same resistor (a resistor is required, the jumper will burn the transistor) we connect the base of the transistor to +24V. The relay should turn on.

If the transistor does not work, it must be checked with an ohmmeter by turning off the power (you can check it before manipulating the resistor). How to check a transistor - is it possible, I won’t write?

The relay may also be faulty.

Subtleties

If the repair has reached this stage without bringing results, then the repair can be considered complex and protracted. Just like this article.

Therefore, I will not go into further details, but if necessary, ask questions in the comments, I will definitely answer.

And yes, it will be better if, along with your questions, you describe the progress of the repairs point by point in the article. And it would be great if there was a photo of the sensor, its boards and a circuit diagram.

Bonus. Reader question about the sensor on LP8072C

Let's consider a motion sensor circuit on a specialized chip LP8072C, which was sent by reader Andrey (see comment to the article dated December 15, 2015)

Sensor circuit for LP8072C

I repeat his question again and answer:

I took out the sensor. Two blocks (power supply from the relay and on the other all the sensors), with 3 wires - 0.5V, 11 contact to the base.

Yes, the circuit is divided into two boards, as in the sensor at the beginning of the article. 0V – GND, on pin 5 of the microcircuit, 5V – power supply, VDD, on pin 13, and output for controlling the transistor.

Looked
13 - VDD 5v.
9 - CDS (photo diode circuit) from a variable resistor changes from 0.4 V to 2 V.
11 - there is 5V constantly - the relay is triggered and the lamp is on, does not depend on CDS.

Everything is correct so far. Just for fun, you can short-circuit the base and emitter of the transistor (for example, with a screwdriver, and the output 5V will drop across the 5.6 kOhm resistor, it’s not scary). The relay and load should turn off. This will indicate that the transistor and power circuits are working.

True, I put it on the table, soldered the wires to 0, and in series to 13, 9, 11 for the voltmeter.
When I measured between 0 and 11, the sensor worked. It was possible to change the duration of lamp burning with a variable resistor.

Between pins 5 and 11? This is just a power output, the voltmeter should not affect it. It turns out that the voltmeter has bypassed the output of the microcircuit, as I recommended above by shorting the base-emitter with a screwdriver. This shouldn’t happen, either the microcircuit is faulty (most likely) or the voltmeter.

But I tried the sensor with a regular 60 W lamp. I was delighted, put everything into the spotlight - and again it was constantly on.
The burning time may become very long.

Your circuit contains an amplifier and a comparator.
There are pins of two op amps here. Maybe they can be something to look at.
I noticed a chain near the red wire in your RC circuit.

Yes, this chain to reduce sparking of relay contacts does not play a role in this case.

I recommend changing the microcircuit. But first, study the case when a measurement was taken and the sensor worked. The fact is that the input resistance of a voltmeter during measurement affects the circuit, and it is better if it is larger. Typically, the input resistance is about a hundred kiloohms, but cheap models can have 20...50 kOhms (depending on the measurement limit). Therefore, take a resistor of about 100 kOhm, or a little less, and connect it in parallel with the output of the microcircuit. Or between the base and emitter of the transistor.

Such a resistor must be built inside the microcircuit, or it is placed between the base and emitter of the transistor, to increase operational reliability. As in the light sensor circuit.

And the microcircuit is most likely faulty (partially), or has left the mode due to external wiring.

Write in the comments how the renovation is going.

Photo of the spotlight and motion sensor, Andrey sent:

Another addition

On February 10, my reader Mikhail sent a photo of the sensor (see the comment for this date), in which the resistor on the board burned out when turned on:

If anyone has such a sensor or its circuit, help Mikhail and tell him the resistor value. Thank you in advance!

I’ll add that the resistor just doesn’t burn, this is a consequence! 90% that after replacement it will burn again!

Another bonus. Sensor repair video

Here's what my colleagues think about repairing motion sensors:

By the way, do you know where the picture on the intro for the video came from? And what is missing from it? ;) My logo!

Improved motion sensor circuit with bug corrected

I am posting a revision of the diagram outlined at the beginning of the article. It (revision) was sent by Alexey Filippov from Lvov:

The essence of the modification is this.

Example of use: Spotlight on the porch of a house. How it works - the light in the hallway is on - the light from the street is on constantly, the light in the hallway is OFF - the spotlight on the street is turned on by the motion sensor (normal mode). There is no need for a separate switch (and wiring) and at the same time the light in the hallway does not turn on when the sensor on the street is triggered, that is, the circuits are decoupled.

I had this modification done at work, assembled in two copies, one at the service center, the other at the warehouse.

When entering the service, it gets dark early in winter, the light in the room is on and the entrance is illuminated from the street for clients until working hours; during the rest of the dark time, the spotlight with the sensor works as it should - in normal mode.

Thanks Alexey!

Another motion sensor circuit

Photo of motion sensor board for repair

Instead of a 100 Ohm 1W SMD resistor (designation 101). I installed a Soviet 2-watt one on the remote wires.

Replacing a resistor when repairing a motion sensor

Thank you all for your attention, if you have questions or comments - welcome to the comments!

All kinds of sensors allow you to automate many processes in everyday life.

Some of them you can make yourself.

Today we will learn how to do it ourselves.

Based on their operating principle, factory-made motion sensors are divided into three types:

ultrasonic;
radio frequency;
infrared.

Ultrasonic (US)

The sensor working area consists of two parts:

ultrasound emitter;
reflected signal analyzer (receiver).

When a moving object appears in the sensor's field of view, changes will appear in the reflected signal. The analyzer will register them and send a signal to a semiconductor switch or relay, causing the circuit to close.

Advantages of the ultrasonic sensor:

is cheap;
atmospheric factors do not affect operation;
“sees” objects made of any material.

Flaws:

range is limited;
does not respond to smooth movement;
causes discomfort in animals (they are sensitive to ultrasound).

Radio frequency (RF)

The principle is the same, only instead of ultrasound, radio waves are emitted.

Advantages:

compactness;
significant range;
the ability to capture moving objects located behind glass or a thin opaque partition;
high accuracy.

Flaws:

are expensive;
are hypersensitive, which is why false positives sometimes occur;
with significant power, they have a negative effect on people and animals who are in the field of view of the sensor for a long time.

Infrared (IR)

They do not emit anything, but only capture infrared radiation, thus determining the temperature of objects. When an object with a given temperature (usually set to 36.6 degrees) appears in the field of view, they are triggered, closing the lamp circuit.

Advantages:

do not have harmful effects on people and animals;
easy to customize;
have an affordable price.

Flaws:

operating temperature range is limited;
do not “see” through materials that do not transmit IR radiation;
react to heating devices.

Ultrasound and RF sensors are called active, IR - passive. The latter are also called pyromodules - from English. PIR, which stands for Passive Infra-Red.

Classification by purpose

Based on their purpose, motion sensors are divided into:

internal (room);
outdoor (street).

The latter are distinguished by their resistance to extreme temperatures and a significant range of action - 500 m or more.

Types of homemade sensors

Homemade motion sensors work on different principles:

reed switch. Reed switch is an abbreviated phrase for “sealed contact”. This is a capsule with two contacts made of ferromagnetic steel, sensitive to the magnetic field. When a magnet is brought close to the reed switch, the contacts in it close, and when removed, they open. Such motion sensors are installed on doors and windows: a reed switch is attached to the jamb, a magnet is attached to the sash. When the sash opens, the magnet is removed from the reed switch, the contacts in it open and power is supplied to the lamp or some kind of signaling device. Of course, this device is not a motion sensor in the full sense of the word. It is rather a door opening sensor;
light. The sensor consists of two parts: a light source and a photocell. When a moving object crosses the line between them, light stops flowing to the photocell-transistor, which leads to the circuit closing;
microwave. When a person approaches a working radio, it reacts - interference appears in the playback. The action of this sensor is based on this phenomenon. It consists of two main parts, an antenna and a microwave generator.

Required tools and materials

To make it you will need only two tools:

The elements and materials needed are:

phototransistor (designated VT1 in the diagram);
(C1);
operational amplifier with feedback (DA1);
feedback resistor to the operational amplifier (R2);
normal (R1);
relay RES 55A;
laser pointer (if the distance between the light source and the photodetector is small, a photodiode can be used instead of a laser);
plumbing gasket;
screw.

You can make a phototransistor yourself from a P417A transistor or any other one that looks like a hat with a brim on 3 legs. The housing cover is dismantled, revealing the semiconductor filling, or a hole is formed in it by cutting off the upper part. When illuminating an open crystal, the device will act like a phototransistor, only with less sensitivity.

The R2 rating is chosen taking into account the fact that as it increases, the gain increases, and this leads to a decrease in the stability of the amplifier. The optimal resistance is 100 kOhm.

Stages of device assembly

The motion sensor is assembled in several steps:

The connector is cut off from the power supply. Next, a multimeter is used to determine the core with a positive charge;
A photodetector is made from the components listed above, connecting them into a circuit.

Photodetector circuit

Then connect the laser pointer to the power supply:

solder two additional wires to the block;
pierce the water gasket with a screw and place this structure in the laser pointer with the head first, so that it rests against the spring contact.

One of the additional wires is connected to the screw, the second is placed in the gap between the gasket and the pointer body.

How to connect a motion sensor: diagram

It is advisable to install a homemade light motion sensor in a doorway - then a person entering the room is guaranteed to cross the line between the light source and the photodetector.

The product will look more elegant if the photodetector circuit is placed in a plastic box with a hole opposite the phototransistor.

Approximate installation of a motion sensor on the street

To exclude the influence of other light sources, the photosensor is darkened and covered with dark light-transmitting material.

Installation height - 1 m from the floor. With this placement, the sensor does not notice pets and the laser completely prevents the laser from entering a person’s eyes (it has a negative effect on the retina). To supply power to the lamp, a RES 55A relay is connected to the sensor.

The connection diagram is as follows:

the winding is connected to the input;
is supplied to one contact;
the second contact is connected to ;
the third is connected to the lamp.

The device works as follows:

under the influence of light, an operating voltage is formed in the photoresistor, causing it to open;
power is supplied to capacitor C1, as a result of which it is charged;
when a light-proof barrier appears between the light source and the photodetector (a person has entered the room), the phototransistor closes and capacitor C1 is discharged;
this leads to a decrease in voltage at point A and, accordingly, at the output to zero. This is facilitated by the operational amplifier DA1;
when the voltage drops, the power source is closed to the lamp via a relay.

The sensor can be made invisible by using an infrared diode instead of a visible light source.

Making a Microwave Sensor

This sensor is assembled according to the diagram below. Here, transistor VT1 simultaneously plays the role of a high-frequency generator of a radio receiver. The voltage set by the bias at the base of transistor VT2 is rectified by the detector diode.

The T1 windings are tuned to different frequencies. In the normal state (there are no moving objects), the amplitudes of the signals cancel each other out and no voltage is applied to the detector VD1.

Schematic diagram of a microwave motion sensor

When moving objects appear that obscure the antenna and distort the radio waves going to it, the amplitudes of the signals are summed up and detected on a diode. This causes VT2 to open.

Settings

In the proposed circuit 1, resistor R1 performs the functions of collector and load. The operating point can be adjusted using it. The optimal resistance is determined by the selection method.

A comparator is required to fine-tune the microwave sensor on and off values (diagram 2). Its role is played by thyristor VS1. It is controlled by a 12 V power relay.

Video on the topic

How to make a lamp with a motion sensor with your own hands:

The process of making a homemade motion sensor for lighting control is not complicated. Even a beginner can cope with this; you just need to carefully study the diagrams and recommendations presented in the article.

Special electronic devices that respond to movement within the range of their sensitive element are becoming increasingly popular among the average consumer. With their help, it is possible not only to protect important objects from penetration by unauthorized persons, but also to control the operation of equipment connected to them (lighters, in particular). Before making a motion sensor with your own hands, you will need to familiarize yourself with the existing varieties of these devices, as well as their connection diagrams.

Types of sensors

Motion sensors detect the appearance of an object in a controlled area in various ways

In accordance with the principle used for generating the control signal, all motion sensors are divided into the following types:

Ultrasonic sensitive elements (US).
Radio frequency (RF) devices.
Infrared devices (IR).
Laser sensors.

Each of these devices uses its own type of radiation, which is detected by a sensitive element. The first type reacts to an ultrasonic signal reflected from a moving object, and the second one works on the same principle, but in the radio frequency spectrum.

Infrared sensors, unlike others, do not use a reflected signal, but detect a moving person or animal by the thermal radiation of their body.

Laser sensors respond to a reflected signal in the wavelength range corresponding to the pump frequency.

According to their purpose, all these products are divided into the following types:

security;
light switches;
switches for household appliances.

The first type of sensors allows you to turn on a powerful spotlight that illuminates the protected areas in front of the house or garage when an unauthorized person enters them. Models of the second type control the lighting of indoor work areas. They turn on the light when a person approaches the waste collection area, for example, and turn it off when he leaves. Sensors that control the operation of household appliances are triggered when a person approaches and connect an electric kettle in the kitchen or a TV in the living room to the network.

When choosing a circuit for a homemade sensitive device, one usually proceeds from the simplicity of its implementation.

Homemade motion sensors

Motion sensor circuit for turning on the light

Do-it-yourself motion sensor circuits are simple enough for anyone to make them at home. The most common options among users are the following:

light sensor;
capacitive sensor;
thermal device assembled on the basis of the Arduino kit

The first in this list is a device consisting of a built-in light source and a transistor photocell placed at a certain distance. When a moving person crosses the communication line, the light beam is interrupted, after which the actuator is activated. Immediately after this, the lamp connected to it turns on. Devices of the second type use the principle of changing the capacity of a room when a person appears in it. Therefore, its main element is a distributed capacitor, consisting of homemade capacitive structures.

The sensor, assembled on the basis of the Arduino constructor, is triggered when the pattern of thermal radiation changes.

Self-production

Independent production of a light-sensitive device begins with the preparation of the necessary tools and material. To assemble it you will need:

electric soldering iron;
measuring device – multimeter;
side cutters and tweezers;
transistor photocell;
operational amplifier (op-amp);
set of parts: capacitor, resistors and relay RES55;
a ready-made power supply that supplies voltage to the circuit.

You also need to stock up on an old laser pointer that serves as a light signal source and a set of wires.

You can make a photocell yourself, using any old transistor (P416, for example) as a basis. To do this, you need to take side cutters, and then use them to “bite out” the transistor cover, leaving a platform with three legs. Under the influence of light, the crystal base of the opened triode will work as a photocell with slightly lower sensitivity.

Assembly order

Motion sensor assembly

An old but working power supply from 4.5 to 12 Volts is taken and the power connector is cut off from it. The tap is designed in the form of two conductors (plus and minus), which are conveniently soldered into the circuit. You can determine the polarity of the power supply using a multimeter.

All subsequent operations look like this:

From the prepared parts, a simple circuit for receiving a light beam from laser illumination is assembled.
It itself is connected to the power supply, for which you will have to use a soldering iron.
The assembled part with the receiving element is placed in a box of suitable size; in this case, the cap of the photosensitive element is brought out.

Upon completion of the assembly operations, you should proceed to installing a homemade sensor and its subsequent connection.

Installation and connection

Various connection schemes

A do-it-yourself light sensor is most conveniently built into the doorway. In this case, a person entering the room will definitely cross the line formed by the pointer beam and the light radiation receiver (photocell).

If the system is located outdoors, the receiver placed in a plastic box is slightly shaded by a homemade canopy during installation. Sometimes for these purposes a piece of light-transmitting material is used to cover the receiving hole in the box. Using such techniques allows you to reduce the influence of other light sources reflected from white surfaces, for example.

The installation height of the pointer and receiver indoors is chosen to be one meter. This arrangement is optimal for most family members and at the same time the device will not operate when moving animals. This height also eliminates the possibility of the laser getting into the eyes of an adult.

Reed relay RES-55A (5 volts)

To turn on and operate the circuit, a relay of the RES 55A type is used, to the winding of which voltage is supplied from the executive part. How the homemade device works:

Under the influence of a light beam in a normal (not turned on) state, a current flows through the photoresistor, leading to its tearing off.
A charge is accumulated on a capacitor connected to the output, creating a certain potential on its plates (the system is in equilibrium).
When an obstacle in the form of a person appears, the photoresistor receiver closes, and the charge accumulated on the plates flows through a resistor connected in parallel.
This leads to a decrease in the potential at the control point of the op-amp to almost zero, as a result of which a low-voltage voltage is supplied to the relay winding.

The relay contacts close the power supply circuit of the lamp, which is instantly supplied with a mains voltage of 220 Volts. After a person passes, the system will remain unchanged as long as the switch remains with the button on.

Manufacturing and setting up a microwave sensor

Schematic diagram of a microwave motion sensor

To manufacture a microwave sensor, experience with high-frequency generator devices will be required. The basis is an amateur circuit of a transistor generator based on a field structure. The receiver is made according to a transformer selective circuit with a key stage on a KT315 transistor loaded onto a detector diode.

Today, presence sensors have become very fashionable to detect movement when a person moves around the room.

When you connect such a device to lighting fixtures, you will receive an automatic system for turning on the lights. Almost anyone can assemble a presence sensor to detect a person on their own. And here the assembly diagram will be the main one. You will learn everything about the assembly process from this article.

Principle of operation

The first thing you need to know when assembling such a device yourself is the principle of its operation.
Note! Many people confuse such devices with motion sensors. But these are different models.
The operating principle of the device is based on the sensor’s response to the location of a person or large animal. The operation of the device is based on the Doppler effect - a change in wavelength and frequency. These changes are recorded by the sensor and transmitted to the device to further turn on the lighting or sound signal. Moreover, the signal arrives at the sensor regardless of whether the object moves or remains motionless. The device is equipped with an antenna and a generator. Without the presence of a reflective antenna signal, the device is in sleep mode. The operating diagram is shown below.

When the device is connected to a light source, in the event of the appearance of any object in the work area, the light is activated. At the same time, to turn on the lighting as such, there is no need for movement (even a slight one).

Where is it used?

Presence sensors are actively used today in the following areas:

“smart home” system for turning on the lights automatically (the connection diagram is shown below). In this situation, it allows you to save electricity consumption significantly;

Connection diagram

security systems;
robotics;
various production lines;
video surveillance systems;
to control electricity consumption, etc.

In addition, interactive toys equipped with similar devices are increasingly appearing. But in most cases, when the device reacts, there is no need to turn on the light. Such products can respond to temperature, ultrasound, object weight and many other parameters. The lighting does not turn on here. The device reacts, for example, by turning on the sound or transmitting a signal to a portable mobile device (for modern models).
Such developments are especially indispensable in the security system. But not every person can afford to purchase such a device. They are quite expensive and may not be affordable. Therefore, some people make such devices with their own hands.

Let's start assembling

In order to assemble the sensor, you will need the diagram below.

In addition to this you will need:

microwave generator;
transistor KT371 (KT368), which must be pre-amplified by KT3102;
comparator;
microcircuit K554CA3.

All the necessary components for assembly can be found on the radio market or in specialized electronics stores.
According to this diagram, it is necessary to assemble and solder the above elements.
According to the given diagram, the sensor will work like this:

the generator produces a microwave signal;
then it is transmitted to the whip antenna;
then the signal is reflected from an object moving in the controlled area;
the result is a frequency shift;
then it is returned to the antenna and microwave generator.

At this stage it will operate as a direct conversion receiver. This is due to the fact that the received signal is converted into infrasonic (low frequency).
After signal conversion, the following happens:

now the low-frequency vibrations already received, reaching the pre-amplifier, are amplified;
they are then transmitted to the comparator and converted into pulses (rectangular).

If the signal is not reflected, then a high level voltage is obtained at the output of the comparator.
A trimmer capacitor is needed to set the frequency. It must be equal to the resonant frequency of the antenna.

Note! This parameter should be selected according to the maximum sensitivity of the sensor.

From a constructive point of view, the device must be made on a printed circuit made of fiberglass. The board must be placed on a plastic case.

Printed circuit (example)

You can use a piece of rigid wire as an antenna. For its manufacture, it is better to choose copper wire. We solder it to the contact pad of the resulting board. The antenna output is carried out through the output on the housing. Experts recommend placing the antenna vertically.
Remember that any shielding objects should not be placed in the immediate vicinity of a self-assembled sensor. In addition, you should know that for the normal functioning of a soldered product, its common wire must have a capacitive connection to the ground.

Final stage

After you have installed the compact device, it should be hung on the inside of the door, as close as possible to the door handle and door lock. The product can also be placed in other places. The main thing is that the controlled area is sufficient.
During installation, it is necessary to ensure that the length of the conductors and leads of the elements is minimal. This will avoid interference, which could result in the device not working properly.
Following the instructions and diagram provided, it is relatively easy to assemble a presence sensor with your own hands. The main thing is to mount all the components in the right order.

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