What kind of LED is in the TV remote control? How to simply check the performance of infrared diodes

An infrared (IR) emitting diode is a semiconductor device whose operating spectrum is located in the near-infrared region: from 760 to 1400 nm. The term “IR LED” is often used on the Internet, although it does not emit light visible to the human eye. That is, within the framework of physical optics this term is incorrect, but in a broad sense the name is applicable. It is worth noting that during operation of some IR emitting diodes, a weak red glow can be observed, which is explained by the blurring of the spectral characteristics at the border with the visible range.

IR LEDs should not be confused with infrared laser diodes. The operating principle and technical parameters of these devices are very different.

Application area

Let’s take a closer look at what infrared LEDs are and where they are used. Many of us encounter them every day without knowing it. Of course, we are talking about remote controls (RC), one of the most important elements of which is the IR emitting diode. Due to its reliability and low cost, the method of transmitting a control signal using infrared radiation has become widespread in everyday life. These remote controls are mainly used to control the operation of televisions, air conditioners, and media players. When you press a button on the remote control, the IR LED emits a modulated (encrypted) signal, which is received and then recognized by a photodiode built into the body of the household appliance. In the security industry, video cameras with infrared illumination are very popular. Video surveillance, supplemented with IR illumination, allows you to organize round-the-clock monitoring of the protected facility, regardless of weather conditions. In this case, IR LEDs can be built into the video camera or installed in its working area in the form of a separate device - an infrared spotlight. The use of high-power IR LEDs in the floodlights allows for reliable control of the surrounding area.

Their scope of application is not limited to this. The use of IR emitting diodes in night vision devices (NVDs), where they perform the function of illumination, has proven to be very effective. With the help of such a device, a person can distinguish objects at a fairly large distance in the dark. Night vision devices are in demand in the military sphere, as well as for covert night surveillance.

Types of IR Emitting Diodes

The range of LEDs operating in the infrared spectrum includes dozens of items. Each individual specimen has certain characteristics. But in general, all IR semiconductor diodes can be divided according to the following criteria:

• radiation power or maximum forward current;
• purpose;
• form factor.

Low-current IR LEDs are designed to operate at currents of no more than 50 mA and are characterized by a radiation power of up to 100 mW. Imported samples are manufactured in an oval 3 and 5 mm housing, which exactly replicates the dimensions of a conventional two-terminal indicator LED. Lens color ranges from transparent (water clear) to translucent blue or yellow. Russian-made IR emitting diodes are still produced in miniature packages: 3L107A, AL118A. High-power devices are produced both in DIP housing and using SMD technology. For example, SFH4715S from Osram in an smd housing.

Specifications

In electrical diagrams, IR emitting diodes are designated in the same way as LEDs, with which they have much in common. Let's look at their main technical characteristics.

Operating wavelength– the main parameter of any LED, including infrared. The passport for the device indicates its value in nm, at which the highest radiation amplitude is achieved.

Since an IR LED cannot operate at only one wavelength, it is customary to indicate the width of the emission spectrum, which indicates a deviation from the declared wavelength (frequency). The narrower the radiation range, the more power is concentrated at the operating frequency.

Rated forward current– direct current, at which the declared radiation power is guaranteed. It is also the maximum permissible current.

Maximum pulse current– current that can be passed through the device with a fill factor of no more than 10%. Its value can be ten times higher than direct direct current.

Forward voltage– voltage drop across the device in the open state when the rated current flows. For IR diodes, its value does not exceed 2V and depends on the chemical composition of the crystal. For example, UPR AL118A=1.7V, UPR L-53F3BT=1.2V.

Reverse voltage– the maximum voltage of reverse polarity that can be applied to the p-n junction. There are instances with a reverse voltage of no more than 1V.

IR emitting diodes of the same series can be produced with different scattering angles, which is reflected in their markings. The need for similar devices with a narrow (15°) and wide (70°) radiation flux distribution angle is caused by their different scope of application.

In addition to the basic characteristics, there are a number of additional parameters that should be taken into account when designing circuits for operation in pulsed mode, as well as in environmental conditions other than normal. Before carrying out soldering work, you should familiarize yourself with the manufacturer’s recommendations on observing the temperature regime during soldering. You can find out about the permissible time and temperature intervals from the datasheet for the infrared LED.

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remote control (RC)

90% of remote controls are defects of two types:

1) some buttons do not work (usually those that were frequently pressed). In this case, you need to cut out a piece of foil and glue it to the rubber base on the contact side. To do this, use silicone glue;

2) often the defect occurs as a result of the remote control falling. Quartz fails. Any remote control can be tested on a portable receiver that has KB and CB waves. You need to bring the front of the remote control closer to the receiver and press any button. Noise will be heard from the emitter (see below).

Restoring the conductive surface of buttons

You need to take polyethylene from fonts (and the like), the tougher the better. Cut a rectangle according to the format of the printed circuit board. Mark on it the centers of the holes corresponding to the centers of the buttons. Next, drill or punch holes with a diameter equal to the diameter of the contact pad.

It is necessary to make all the holes that are on the printed circuit board itself. We make a conductive layer. Take baking foil (new, not wrinkled), and stick tape on it. We cut out a rectangle according to the format of the board, make technological holes, as on the board (you need to cut a hole under the LED). We assemble it - we put foil on the buttons (adhesive tape on the buttons), and a board on top. Then close the remote control.

The secret to restoring conductivity

graphite layer on remote controls

For this, a graphite emulsion is prepared: “earplugs” are dissolved in any solvent for nitro paints. After this, graphite is gradually added to the solution - the finer the better. For this you can use a regular pencil.

This solution should be used to cover the torn section of the graphite conductor.

Option to check remote controls

For faulty video units and TVs, there are always IR signal receiver units in stock. They are soldered into the screen and usually have 3 pins.

The LED is connected directly to the terminals of the block: “+” - to the “+” power supply, “-” - to the output. Stabilized power supply - 3…9 V.

The quartz in the remote control can also be assessed by the blinking frequency of the LED (they “glitch” quite often).

How to increase the efficiency of remote control

With the deterioration (over service life) of the electrical characteristics of the batteries (loss of battery capacity and decrease in battery current and voltage), effective operation requires a proportionally closer proximity of the remote control to the IR signal receiver. This is the first sign of the need to replace batteries.

The operating range of a conventional remote control with one IR emitting diode, which usually does not exceed 5-6 m in open areas (unfocused flow), and in conditions of interior obstacles, 10-12 m can be increased 2 times by installing in series with the standard one, a similar IR diode. In this case, the additional IK diode must be turned on in the forward direction and installed next to the first one. To do this, you will need to carefully disassemble the remote control housing, and depending on the design features of the installation of the basic IR diode (behind a protective glass screen or in an open state with a protruding working surface of the diode outside the remote control housing), drill a hole to accommodate another IR diode.

If a similar IR emitting diode is not available or, as often happens, it is impossible to determine exactly the type of standard IR diode used in the remote control (for remote controls with a circuit supply voltage of up to 6 V), it is allowed to switch on AJI156A, AJI147A, AJI164A9, AL164A91 (foreign analogs of L -315EIR, L-514CIR). They have a transparent bulb color, forward current reaches 100 mA, wavelength 920-940 nm, radiation power 8-10 mW.

There is no need to increase the supply voltage of the electronic circuit of the remote control pulse shaper, just as there is no need for other intervention in the standard circuit. Increasing the range of the remote control has been tested with the Setro STV-2080MH models, the remote control of the MAX-930 minisystem manufactured by Samsung, the remote control of the W131W video player and others.

The easiest way to check the remote control

This method can be used to quickly check the remote control anywhere, even in the field, if necessary.

To do this, you will need a simple radio receiver with a medium wave range, for example, “0lympic-402” or “Selga-401-405”, produced by the domestic industry. Today, there are many such radio receivers that receive radio waves in the medium wave range, and their “Chinese” names make one’s eyes dazzle.

When testing the remote control using the proposed method, it is not the presence of IR radiation that is checked, but radio interference created by the electronic components of the remote control is recorded. It is known that each radio element is, to one degree or another, a source of electromagnetic interference “noise” and weak radiation of radio waves. At a short distance from the radiation source, these “noises” are recorded by a “Selga” radio receiver.

Throughout the entire medium wave range, an intermittent audio frequency signal (with a frequency of approximately 400 Hz) will be heard in the radio receiver if any button is pressed on a nearby (at a distance of up to 1 m) button. While the button is pressed, the radio emits an audio frequency signal through the speaker. Using the same method, you can control the effectiveness of pressing all the buttons on the remote control, because it is important that they are all pressed with approximately the same force. This method is especially important when the remote control, for example, for a TV in the kitchen, is bought at the market or “from hand”. Everything is possible here.

In order not to buy a “pig in a poke,” it is wise to take with you a portable radio receiver with the ability to receive medium waves and, when checking, insert batteries into the remote control and check the pressing of each button on the remote control. Each press of a working remote control will certainly be accompanied by a sound signal in the radio receiver (over the entire medium wave broadcast range) from a distance of up to 1 m.

The second life of radios like “Selga-404” and similar ones does not end with this recommendation. This type of radio receiver, configured to receive medium waves, can also effectively control the operation (from a short distance of up to 1-2 m) of IR transmitting devices of various security systems, for example, alarms or the operation of remote transmitting devices (bugs) that transmit information via IR LEDs .

In addition to the Selga radio receiver of various modifications, any (including modern) radio receiver that works reliably in the medium wave range is suitable for checking the remote control and performing related tasks.

You will have to check the serviceability of the IR emitting diode in the remote control using another method (for example, the first one recommended in this article), however, for checking the operation of the remote control electronics, this method has no analogues in its simplicity.

I. Ivanov

You can check the operation of the remote control in the absence of a TV using an infrared photodiode (PD). For example, the domestic FD-8K would be suitable. The PD leads are connected to the ground and signal probes of the oscilloscope. The remote control is placed coaxially with the FD close to its window. Press any of the buttons on the remote control. In this case, a PWM signal with an amplitude of 0.2...0.5 V should appear on the oscilloscope screen.

The circuits of most television remote controls are the same and include:
- a command generator microcircuit with a quartz resonator;
- an amplifier consisting of one or two transistors;
- LED (or two);
- keyboard and contact field.

In addition, some remote controls have an indicator LED that registers the command.

Let's consider possible malfunctions of the remote control, methods for detecting and eliminating them.

1. No signal from the remote control

Check the condition of the batteries. If the supply voltage is less than 2.5 V, the batteries must be replaced. For voltages greater than 2.5 V, check the short circuit current Is with a multimeter. For serviceable elements it should be equal to 1...3 A. If Is
Then open the remote control. This operation requires certain skills and accuracy. The main task in this case is not to leave scratches on the remote control body and not to break the latches. To open the remote control, use a regular screwdriver with a thin blade (currently there are special screwdrivers on sale with a blade 10...20 mm wide and 0.5 mm thick with a short handle).

They begin to open the remote control from the side where the batteries are located, and first disconnect one side of the bottom cover to the entrance window, and then the other in the same way, after which the cover is easily removed.

Conduct an external inspection of the condition of the printed circuit board and keyboard contacts.

Traces of dried liquid on the contact field are removed using a cotton swab moistened with alcohol. Conductor breaks are eliminated by soldering jumpers made of thin wire.

Check for contact between the graphite jumpers and the printed conductors.

By closing any pair of contacts on the printed circuit board, use an oscilloscope to check the presence of a PWM signal at the cathode of the LED.

If there is no signal and the DC voltage is zero, check the continuity of the LED. A working LED should have a resistance in the forward direction of several tens of ohms, and in the reverse direction - several hundred kilo-ohms. A faulty LED must be replaced.

A fairly common defect is a break in the LED output as a result of mechanical impact, for example, after the remote control is dropped.

Check the passage of the PWM signal from the output of the microcircuit to the LED.

2. There is no signal at the output of the remote control chip

lack of supply voltage to the microcircuit;
malfunction of the quartz resonator;
the presence of two or more pairs of closed contacts on the printed circuit board;
breakage of conductors between the microcircuit and the contacts of the printed circuit board;
microcircuit malfunction.

First, check the supply voltage of the microcircuit: it must be at least 2.5 V.

The performance of the quartz resonator is checked by closing any of the pairs of contacts on the printed circuit board. If there is no generation, then most likely the microcircuit is faulty.

3. There is no signal from the remote control. There is a signal at the output of the microcircuit

Possible causes of the malfunction:
lack of amplifier supply voltage;
malfunction of amplifier elements;
LED malfunction.

Using an oscilloscope, check the presence of a signal at the cathode of the LED. If there is no signal here, check its passage from the output of the microcircuit to the LED.

The most common defects in this case are failure of the transistor in the output stage of the amplifier, violation of the soldering connections, and the terminals of the amplifier elements.

4. There is no signal from the remote control. The photodiode indicates the presence of a constant voltage level. Batteries drain quickly. The LED is constantly open and a significant current flows through it

Possible reasons:
breakdown of one of the amplifier transistors;
the presence of two or more pairs of closed keyboard contacts;
microcircuit malfunction.

The serviceability of the transistors and the presence of closed contacts are checked by dialing. The serviceability of the microcircuit is checked by replacement.

5. Some command is constantly sent from the remote control when the keyboard buttons are not pressed. Batteries drain quickly

Possible causes of the malfunction:
reducing the insulation resistance between the terminals of the microcircuit or the contacts of the printed circuit board;
reducing the insulation resistance between the graphite jumper and the printed conductor passing under it;
microcircuit malfunction.

Thoroughly wash the microcircuit terminals with alcohol, removing traces of rosin, dust, and dirt. On the printed circuit board, wipe the contacts with a cotton swab moistened with alcohol. Solder the corresponding pins of the microcircuit from the board. If after this commands from the remote control continue to arrive, the chip is changed. If the signal disappears, look for a current leak from the graphite jumper to the printed conductor. The conductor is cut off on both sides and a jumper made of insulated wire is installed (unsoldered) instead.

6. One or more remote control buttons do not work

Possible causes of the malfunction:
increasing the resistance of the keyboard's closing contacts;
crack on the board.

Use a multimeter to measure the resistance of the contacts. For working buttons it is 2...5 kOhm. If the resistance is more than 10 kOhm, the button is faulty. In this case, either change the entire rubber band or repair the contact. Special repair kits for remote controls are available for sale. They consist of contacts made of conductive rubber, which are glued to the faulty keyboard contacts with silicone glue included in the repair kit.

The presence of cracks is determined visually. Damaged printed conductors are restored using thin wire jumpers.

Most modern remote controls provide the ability to convert them into a service remote control. The essence of the modification is to install a new or rearrange an existing jumper on the printed circuit board, and the installation location on the board is indicated.

As an example, the figure shows the RM-836 remote control for SONY TVs with the top cover removed. After installing the jumper in pos. 1

The functionality of the image format change button changes.

Now, after pressing this button twice, the TV is switched from operating mode to service mode.

Repair of remote controls.

M.Kireev

After several years of operation, the functioning of remote controls for televisions and other equipment often malfunctions. This is possible for several reasons: violation of the integrity of the soldering of electronic components, oxidation of the spring contacts in the battery compartment, complete or partial abrasion of the conductive layer applied to the ends of the buttons (Fig. 1),

Which are the most commonly used.

To eliminate the last defect, a simple method is proposed that has been tested for several years and does not require large expenses. On the end of the button, cleaned and degreased, for example with alcohol, the functionality of which needs to be restored, apply one layer of quick-drying glue, for example, “Secunda”, and then stick on a piece of aluminum foil slightly larger than the area of ​​the end of the button. After the glue has hardened, the protruding foil is carefully crimped with tweezers (Fig. 2).

Practice has shown high reliability and trouble-free operation of remote controls repaired in this way.

If you have to repair remote controls frequently, you can make a device for monitoring their performance, assembled from available parts (Fig. 3).

The DA1 chip serves to amplify the signal coming from the infrared photodiode VD1 and generate a sequence of output pulses that goes to the divider DD1.1. When you press any button on a working remote control, the VD2 LED will blink at a frequency of several hertz. The device is conveniently mounted in a housing measuring 100 x 40 x 30 mm (Fig. 4).

The DA1 chip can be replaced with domestic analogs KR1054UI1, KR1054ХА3, KR1056UP1, KR1084UI1, taking into account the difference in pinouts.

Repair & Service

[email protected]

Today in radio electronics there are a wide variety of products used to create high-quality and effective lighting. One such product is an infrared diode type.

To use it to create backlighting, you need to know not only where they are used, but also their features. This article will help you understand this issue.

Features of diodes operating in the infrared range

Infrared LEDs (abbreviated as IR diodes) are semiconductor elements of electronic circuits, which, when current passes through them, emit light in the infrared range.

Note! Infrared radiation is invisible to the human eye. This radiation can only be detected by using stationary video cameras or mobile phone video cameras. This is one way to check whether a diode operates in the infrared spectrum.

High-power LEDs (for example, laser type) in the infrared spectral range are produced on the basis of quantum-sized heterostructures. An FP type laser is used here. As a result, the LED power starts at 10 mV, and the limiting threshold is 1000 mV. Housings for this type of product are suitable for both 3-pin and HHL types. As a result, the radiation appears in the spectrum from 1300 to 1550 nm.

IR Diode Structure

As a result of this structure, a high-power laser diode serves as an excellent source of radiation, due to which it is often used in fiber-optic information transmission systems, as well as in many other areas, which will be discussed below.
The infrared laser diode type is a source of powerful and concentrated laser radiation. In its work, the laser principle of operation is used.
Power diodes (laser type) have the following technical characteristics:

Note! Due to the fact that the product emits light in the infrared range, such familiar characteristics as illumination, power of emitted light flux, etc. don't fit here.

Graphic display of solid angle in 1 sr

• such LEDs are capable of generating waves in the range of 0.74-2000 microns. This range serves as the limit when radiation and light have a conventional division;
• power of generated radiation. This parameter reflects the amount of energy per unit time. This power is additionally tied to the dimensions of the emitter. This parameter is measured in W per unit of available area;
• intensity of the emitted flux within the frame of the volumetric angle segment. This is a rather conditional characteristic. It is due to the fact that, with the help of optical systems, the radiation emitted by the diode is collected and then directed in the required direction. This parameter is measured in watts per steradian (W/sr).

In some situations, when there is no need for a constant flow of energy, but pulsed signals are sufficient, the above-described structure and characteristics make it possible to increase the power of energy emitted by a radio circuit element several times.

Note! Sometimes in the characteristics of infrared diodes, indicators for continuous and pulsed operating modes are distinguished.

How to check functionality

Checking the IR diode

When working with this element of the electrical circuit, you need to know how to check its operation. So, as already mentioned, you can visually check the presence of this radiation using video cameras. Here you can evaluate performance using conventional mobile phone video cameras.
Note! Using video cameras is the easiest way to check.

This IR element in the remote control is easy to check; you just need to point it at the TV and press the button. If the system is working properly, the diode will flash and the TV will turn on.
But you can empirically check the performance of such an LED using special equipment. A tester is suitable for these purposes. To test an LED, the tester should be connected to its terminals and set to the mOm measurement limit. After that, we look at it through a camera, for example through a mobile phone. If a beam of light is visible on the screen, then everything is in order. That's the whole test.

Scope of application of IR diodes

At this point in time, infrared LEDs are used in the following areas:

• in medicine. Such elements of radio circuits serve as a high-quality and effective source for creating directional illumination for a variety of medical equipment;
• in security systems;
• in an information transmission system using fiber optic cables. Due to their special structure, these products are capable of working with multimode and single-mode optical fiber;
• research and scientific spheres. Such products are in demand in the processes of pumping solid-state lasers during scientific research, as well as illumination;
• military industry. Here they have the same wide application as illumination as in the medical field.

In addition, such diodes are found in various equipment:

• devices for remote control of equipment;

IR diode in the remote control

• various control and measuring optical instruments;
• wireless communication lines;
• switching optocoupler devices.

As you can see, the scope of application of this product is impressive. Therefore, you can purchase such diode components for your home laboratory without any problems; they are sold in abundance on the market and in specialized stores.

Conclusion

Today there is no doubt about the effectiveness of high-power infrared LEDs. This is confirmed by the fact that such elements of electrical systems have a wide range of applications. Due to their structure, IR LEDs are distinguished by impeccable performance characteristics and high-quality work.

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LEDs in remote controls rarely fail. Fortunately, anyone who knows how to hold a soldering iron can replace this element. You have absolutely correctly diagnosed the problem, but the lack of light may also indicate a breakdown of the quartz resonator, which happens much more often, since the resonator can fail when the remote control is dropped on a hard surface.

If you are sure that it is the LED that is faulty, then you can use a diode from another remote control or purchase a new one. The main parameters of IR LEDs are overall dimensions, angle and radiation power, and wavelength. In modern devices, only the dimensions of the element are decisive. The remaining parameters are not so significant. The maximum range of reliable operation or the need to accurately point the remote control at the device may change.

To replace the diode, you need a low-power soldering iron with a power of 25–40 W, no more, since when working with a powerful tool there is a high risk of peeling off the printed tracks. Also for work you need a small piece of low-melting solder (POS-60 or POS-90) and flux (for example, ordinary rosin). Under no circumstances should you use soldering acid used for soldering ferrous metals! The remote control will stop working in a couple of days, and the printed conductors will simply disappear in the solder joints.

When replacing an LED, the main thing is not to confuse the switching polarity. Typically, diodes have different terminal shapes. It makes sense to call them using the device if the switching polarity is indicated on the board. The diode conducts current when the positive probe is connected to the anode. Please note that not all instruments can be used to test LEDs.