Motion sensors are now sold in almost all home appliance stores. A motion sensor for lighting is used in everyday life, for example, in entrances. Of course, you paid attention to the lamps that light up when you approach them? This is one example of the use of motion sensors in everyday life, and there are many more such examples. The movement or movement sensor is used in home and industrial alarm systems, they are in robotics and automation circuits, measuring the speed of an electric motor, etc. But in addition to industrial use, the motion sensor can also be used in everyday life. Moreover, if you make a motion sensor with your own hands, then knowing the scheme of its operation, you can use such a device to turn on or off any household appliances.
Let's look at the main parts of the product. The first thing you need to start with to make a motion sensor with your own hands is to provide power to it. The power supply should be primarily safe, have as small dimensions as possible, and be designed for continuous operation under load. Good for this purposea standard power supply for charging batteries or any other with an output voltage of five volts. Making a motion sensor with your own hands is quite simple, it does not require scarce or expensive parts.
Now we select a photocell, any one is suitable for our purposes, its area does not matter, a little later we will find out why. Photocell cathode
connect to the positive output of the power source. Now the current limiting of the photocell, the rated current must flow through it, otherwise it will simply burn out. According to Ohm's law, we calculate the resistance value, and solder it to the anode terminal of the photocell.
Now the tuning resistance, 10 kOhm is enough, one of the conclusions is soldered to the minus supply, the second - to the free end of the current-limiting resistance. Now we assemble the emitter follower circuit using an npn junction transistor. Its base is soldered to the free end of the tuning resistance. The collector is directly soldered to the positive terminal of the power source, and a small power relay with a nominal voltage of five volts is included in the emitter circuit. We solder the other end of the relay coil to the negative terminal of the source. We assemble the relay contacts according to the self-pickup scheme, that is, the first time the motion sensor is triggered, the relay will pull up and provide power to itself with its contacts.
Free relay contacts go to a load, such as lighting or a tape recorder, it all depends on your imagination. As you can see, make the motion sensor your ownhands is easy. The main thing in this case is not to overload the contacts, because the relay used in the circuit is low-power. But in the form of a load, we can use another relay, with more powerful contacts, which will provide you with the load you want.
To reset the device to its original state, it is enough to briefly interrupt its power supply. Insert a small self-resetting switch into the power circuit. As a source of radiation, you can use a laser pointer, providing it with constant power from our source. Now it is clear why the area of the photocell did not play any role, the radiation of the pointer is monochrome and the light beam does not change in area.
