How to make a motion sensor at home

Special electronic devices that respond to movement in the range of their sensing element are becoming more and more popular with ordinary consumers. With their help, it is possible not only to protect important objects from the penetration of unauthorized persons, but also to control the operation of equipment connected to them (illuminators, 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 with the schemes for their inclusion.

Types of sensors

Motion sensors in various ways determine the appearance of an object in the monitored area

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

  • Ultrasonic Sensing Elements (US).
  • Radio frequency (RF) devices.
  • Infrared (IR) devices.
  • Laser sensors.

Each of these devices uses its own type of radiation, recorded by a sensitive element. The first type reacts to an ultrasound signal reflected from a moving object, and the second works according to the same principle, but already in the radio frequency spectrum.

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

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

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

  • security;
  • lighting switches;
  • household appliances switches.

The first type of sensors allows you to turn on a powerful searchlight 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 area of ​​the garbage collection, for example, and turn 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 scheme for a homemade sensitive device, they usually proceed from the simplicity of its implementation.

Homemade motion sensors

Motion sensor circuit for turning on the light

DIY-assembled motion sensor circuits are simple enough so that everyone can make them at home. The most common among users are the following options:

  • 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 triggered. Immediately after this, the luminaire connected to it turns on. In devices of the second type, the principle of changing the capacity of a room when a person appears in it is used. Therefore, its main element is a distributed capacitor, consisting of self-made capacitive structures.

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

Self-production

Self-production of a light sensitive device begins with the preparation of the necessary tool and material. To build it you will need:

  • electric soldering iron;
  • measuring device - multimeter;
  • side cutters and tweezers;
  • transistor photocell;
  • operational amplifier (OA);
  • a 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, which serves as a light source and a set of wires.

The photocell can be made independently, based on any old transistor (P416, for example). To do this, you need to take side cutters, and then use them to "bite out" the transistor cover, leaving the platform with three legs. Under the influence of light, the crystalline base of the opened triode will act as a photocell with a slightly lower sensitivity.

Assembly order

Assembling the motion sensor

An old, but working power supply unit from 4.5 to 12 volts is taken, the power connector is cut off from it. The tap is made 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:

  1. A simple diagram of the receiver of the light beam from the laser illumination is assembled from the prepared parts.
  2. She herself is connected to the power supply, for which you will have to use a soldering iron.
  3. The assembled part with the receiving element is placed in a box of a suitable size; the cap of the photosensitive element is then pulled out.

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

Installation and connection

Various connection schemes

A hand-made light sensor is most conveniently embedded in a doorway. In this case, a person entering the room will necessarily 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 during installation with a homemade visor. Sometimes a piece of light-transmitting material is used for this purpose, covering the receiving opening in the box. Using such techniques can reduce the influence of other light sources reflected from white surfaces, for example.

The height of installation of the pointer and receiver indoors is chosen equal to one meter. This arrangement is optimal for most family members and, at the same time, the device will not work when the animals are moving. This height also excludes 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 RES 55A relay is used, to the winding of which voltage is supplied from the executive part. The procedure for the operation of a homemade device:

  1. Under the action of the light beam in the normal (not switched on) state, a current flows through the photoresistor, leading to its detachment.
  2. A charge accumulates on the capacitor connected to the output, which creates a certain potential on its plates (the system is in equilibrium).
  3. When an obstacle in the form of a person appears, the photoresistor-receiver closes, and the charge accumulated on the plates flows down through a resistance connected in parallel.
  4. This leads to a decrease in the potential at the control point of the op-amp to almost zero, as a result of which the low-voltage voltage is supplied to the relay coil.

The relay contacts close the luminaire power circuit, which is instantly supplied with a mains voltage of 220 volts. After a person has passed, the system will remain unchanged as long as the switch remains with the button turned on.

Manufacturing and setting up a microwave sensor

Schematic diagram of a microwave motion sensor

Manufacturing a microwave sensor will require experience with high frequency generator devices. An amateur circuit of a transistor generator on a field structure is taken as a basis.The receiver is made according to a transformer selective circuit with a key stage on a KT315 transistor, loaded onto a detector diode.

The system works like this:

  1. In the absence of a moving object, the amplitudes of the signals of the generator and receiver are approximately equal and mutually compensated.
  2. For this reason, the voltage at the input of the key and the detector is zero and the relay connected to the output does not work.
  3. When a person appears in the sensitivity zone, the balance of signals is disturbed and, as a result, voltage appears at the output of the circuit.
  4. It is fed to the relay coil, when triggered, 220 volts through its contacts are fed to the lamp.

To configure the system, a variable resistor is provided in the circuit, the value of which determines the position of the operating point of the output transistor. When it changes, the moment of its actuation is corrected - the sensitivity of the circuit.

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