Infrared Barrier

As you know, in addition to the visible light spectrum, there is also infrared radiation, which is not perceived by the human eye. It is often used in remote controls to transmit various commands. An interesting fact is that in order to “see” infrared light, it is enough to direct the lens of a digital camera to the infrared emitter of the console and press keys on it. At the same time, a luminous dot will be visible on the screen of the camera - this is an infrared LED. Infrared rays in electronics allow you to create such an interesting device, which is called the infrared barrier. It consists of two parts - the transmitter and the receiver. The transmitter is a conventional IR LED that receives bursts of pulses. The receiver of these bursts of pulses continuously catches and detects. When there is a clear visible connection between the receiver and transmitter, i.e. the light freely “flies” to the receiver; a logical zero is set at the output.But as soon as a foreign object appears in the zone of action, the connection is instantly broken and the receiver signals this. It is possible to use such a barrier, first of all, in security alarms, because infrared radiation cannot be seen with the naked eye. The advantage of this particular scheme is that the infrared LED in it does not glow continuously, but is pulsed. Firstly, it prolongs the life of the LED itself and reduces current consumption, and secondly, it is a good means of protection against false alarms, so the circuit can be safely used even on the street when direct sunlight strikes the receiver.

Transmitter diagram

Infrared Barrier
The transmitter circuit is based on the NE556 dual integrated timer, which generates pulses for the emitting LED1 LED, and the R2 resistor sets the radiation power. All other circuit elements must strictly comply with the specified nominal value in order to comply with the desired frequency of the generator. D1 - any low-power diode, for example, 1N4148, 1N4007, KD521.

Receiver circuit

Infrared barrier
The key element of the circuit is a special receiver of the IR signal,denoted as TSOP (Temic Semiconductors Opto Electronics Photo Modules). You can find it in any TV that has a remote control. This is suitable for any receiver designed for a frequency of 36 kHz, for example, TSOP1736. This receiver controls the gate of the field-effect transistor VT1. Since the signal from the output of the receiver is about 5 volts, then the transistor must be applied with logic control, for example, IRL520 or any other of the IRL series. In extreme cases, you can put a regular field, for example, IRF540, IRF740, IRF630, but it will not open completely. LED1 indicates the output status of the circuit. When the visible connection between the receiver and the transmitter is not broken, the output voltage is zero, LED1 is off. As soon as a foreign object appears in the zone of action, LED1 lights up and the voltage at the OUT output becomes equal to the supply voltage. D1 on the circuit - a 5 volt zener diode, you can apply, for example, 1N4733.
Infrared barrier

Assembling the infrared barrier

Each scheme is assembled on its own printed circuit board, the TSOP receiver and the IR LED are displayed on the wiring. The boards are made using the LUT method, below are a couple of process photos:
Infrared barrier
Infrared barrier
As with the creation of any electronic device, first small parts are soldered to the board - resistors, diodes. Then the capacitors, and after them everything else. It is advisable to install the microcircuit in the socket, and for convenience, connect the power wires through the terminal blocks. After soldering, flush the remaining flux from the board, ring the tracks to the closure.
Infrared barrier
Infrared barrier
Infrared barrier

Setup and testing

After assembly, you can apply power to the boards. The supply voltage of both circuits is 9-12 volts. After switching on, it is necessary to make sure that the voltage on the cathode of the Zener diode in the receiver circuit is approximately 5 volts. If it is higher, you need to check the performance of the Zener diode and the resistor R2, otherwise the TSOP receiver may burn. After starting the transmitter, you can look at the LED through the lens of the camera, it should glow a little.It is advisable to place the LED into a tube with a length of 3-4 centimeters so that the light is not scattered around, but was directed strictly in one direction.
Infrared Barrier
Now you can direct the handset with a LED to the receiver and see what happens. When there is a visible connection between them, the blue LED is turned off, this can be seen from the photo.
Infrared barrier
Now we will place a piece of plywood in the path of the IR radiation flow, the connection between the receiver and the transmitter will be lost and the blue LED will immediately light up.
Infrared barrier
You can experiment with different materials. Paper and transparent plastic transmit infrared radiation, so the IR barrier does not react to them. But metal, wood, human hand or other dense materials are an obstacle to the rays, as seen in the video.


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