Scheme of remote control of devices. IR receiver circuit for remote control of electrical appliances Simple IR receiver circuit

IR REMOTE SYSTEM ON CHINESE MICROSCIRCUIT

Now in our country there are a lot of different Chinese electronics, both finished and various parts and components, and so on. Various flying-driving toys on radio control or on IR control are very popular. Most of them are based on the same chipset: SM6135-SM6136, respectively, the encoder and decoder of the control system. These microcircuits can be obtained from faulty toys or simply bought in a store.

Here I want to show how with these microcircuits it is possible to organize a five-command remote control on IR rays, for example, to control a makeshift audio center or maybe a robot.

The figure shows the remote control and the decoder.

Remote control on the left, on SM6136. As you can see, there are very few details and the circuit can be made very compactly. Buttons S1-S5 are used to issue commands. Commands are transmitted in a certain sequence of bursts of pulses. The bursts of pulses are filled with modulating frequency. This modulating frequency, as well as the equivalent frequency of transmitting the command pulse signal, depends on the frequency of the clock generator, which is set by resistor R1. The modulation frequency of the bursts is equal to half the frequency of the clock generator, which can be measured at control pin 13 D1.

The pulsed modulated signal is fed to the key on VT1 and through it to the IR LED HL1. The current through HL1 is limited by resistor R3. HL1 LED - any IR LED from the TV remote control with 3V power supply.
HL2 - command transmission indicator.

The receiving circuit is shown on the right, on the SM6135 chip. Remote control messages are received by the integral photodetector FL1. This is a standard TV remote control photodetector, for a modulating frequency of 38 kHz. On the transistor VT2 - inverter. And the commands appear in the form of logical units on pins 7, 6, 10. 11, 12 D1. The clock frequency is set by resistor R4.

Setting
Start with the remote. By measuring the frequency on pin 13 D1, set it equal to the double frequency required for pairing with the photodetector. That is, if it is SFH506-38, that is, the frequency is 38 kHz, then pin 13 of D1 should be 76 kHz.
Then, while sending and receiving commands, adjust R4 so that commands are received, and with the greatest range.

The same SM6136/6135 kit is also used in radio control systems for models and toys. In this case, the command pulses are taken from the 8th pin of the SM6136, on which they are not filled with modulating pulses, that is, a purely command code, without pulse filling. This code is applied to the transmitter modulator.
The receiving part is also different, since it uses the amplifying stages of the SM6135 chip (pins 1-3, 14-16). At these stages, an amplifier circuit is assembled for the signal coming from the superregenerative detector.

One of the possible radio control schemes for the model is shown in the second figure.

Having assembled the JDM programmer, we begin to search for some simple scheme to repeat. Quite often, these are banal flashing lights on LEDs or clocks on LED indicators, but the first option has almost no practical application, and the second is often not suitable, not because it is undesirable, but because a radio amateur, especially a beginner or living in the outback, does not always have necessary components (for example, a quartz resonator or LED indicators).

I replaced the TSOP1738 photosensor with a TSOP1736, but you can experiment with similar parts taken from faulty equipment.

The microcontrollers indicated in the diagram are flashed with different firmware - both firmware options can be downloaded from the site mentioned above.

The relay can be used for any winding voltage of 12 volts.

A little about the rest of the details, since the denominations of some of them are not very well read on the diagram:
C1 - 220uF 25V;
C2 - 220 uF, at least 10 V;
C3 - 0.1 uF (here a typo crept into the author's circuit - the next capacitor, electrolytic, should have serial number 4);
C4 - 4.7uF 10V;
R1 - 330 Ohm;
R2 - 1K;
R3 - 4.7 K;
T1 - BC547, KT315 or other similar N-P-N structure transistors;
LED - LED of any type and color you like;
D1 - 1N4148, 1N4007 or equivalent;
Button - without fixation.
Stabilizer - any 5 volt.

Remote control of a VCR, TV, stereo or satellite receiver can be used to turn off and on various household electrical appliances, including lighting.

Do-it-yourself remote control, the diagram of which is given in this article, will help us with this.

Description of the operation of the IR remote control system

The following mechanism is used for remote control of devices. On the remote control, press and hold an arbitrary button for 1 second. The system does not respond to a short press (for example, while controlling the music center).

In order to exclude the response of the TV to the control of devices, it is necessary to select unused buttons on the remote control or use the remote control from the device turned off at this time.

circuit diagram remote control is shown in Figure 1. A special chip DA1 amplifies and generates the electrical signal of the photodiode BL1 into electric pulses. A comparator was built on radio elements DD1.1 and DD1.2, and a pulse generator was built on radio elements DD1.3, DD1.4.

The state of the control system (on or off load) controls the trigger DD2.1. If the direct output of this trigger is log 1, the generator will operate at a frequency of approximately 1 kHz. Pulses will appear on the emitters of transistors VT1 and VT2, which will go through the capacitance C10 to the control output of the triac VS1. It will fire at the beginning of each mains voltage half cycle.

In the initial position, on pin 7 of the DA1 chip, there is a log 1, the capacitance C5 is charged through the resistances R1, R2 and at the input C of the trigger DD2.1 log 0. If IR radiation signals from the remote control go to the BL1 photodiode, pin 7 of the DA1 chip will be signals, and the capacitance C5 will be discharged through the diode VD1 and the resistance R2.

When the potential at C5 drops to the lower level of the comparator (after 1 second or more), the comparator will switch and a signal will be sent to the trigger input DD2.1. The state of the trigger DD2.1 will change. This is how devices switch from one state to another.

Microcircuits DD1 and DD2 can be used similar from the series K564, K176. VD2 - a zener diode for a voltage of 8-9 volts and a current of more than 35 mA. Diodes VD3 and VD4 - KD102B or similar. Oxide tanks - K50-35; C2, C4, C6, C7 - K10-17; C9, C10 - K73-16 or K73-17.

Setting up the IR remote control system

It consists in selecting the resistance R2 of such a value that the switching takes place after 1 ... 2 s. If an increase in the value of this resistance will lead to the fact that the capacitance C5 will not be discharged to the threshold voltage, it is necessary to double the capacitance C5 and re-adjust.

Capacitance C6 should be set if the duration of the front of the pulse going from the comparator to the trigger is excessively large and it will switch unstably.

If the remote control used does not allow you to control the device without interfering with the TV, it is possible to assemble a home-made remote control, which is a generator of rectangular signals with a repetition rate of 20 ... 40 kHz, operating on an IR emitting diode. Variants of a similar remote control on the timer KR1006VI1 (

Yakorev Sergey

Introduction

V Internet networks lot simple devices based on PIC16F and PIC18F family controllers from Microchip. I bring to your attention a rather complicated device. I think this article will be useful to everyone who writes programs for PIC18F, since you can create your own real-time system by taking the source code of the program. There will be plenty of information, ranging from theory and standards to hardware and software implementation this project. Assembly source code is provided with full comments. Therefore, it will not be difficult to understand the program.

Idea

As always, everything starts with an idea. We have a map of the Stavropol Territory. There are 26 districts of the region on the map. The map size is 2 x 3 m. It is necessary to control the highlighting of selected areas. Control should be carried out remotely via an infrared control channel, hereinafter simply IR or IR remote control. At the same time, control commands must be transmitted to the PC-based control server. When you select an area on the map, the management server displays additional information on the monitor. By commands from the server, you can control the display of information on the map. The task has been set. In the end, we got what you see in the photo. But before all this was realized, it was necessary to go through some stages and solve various technical problems.

View from the mounting side.

Device operation algorithm

From the remote control, the information display control system should be controlled no more difficult than selecting a program on TV or setting a track number on a CD. It was decided to take the remote ready from the Philips VCR. The choice of the number of the district is set by successive pressing of the buttons of the remote control "P +", then two numeric buttons of the number of the district, we finish entering "P-". The first time you select an area, it is highlighted (the LEDs turn on), and the second time you select it, the selection is removed.
Card management protocol from a PC management server.

1. Outgoing commands, ie. commands coming from the device to the PC:

1.1. When the power is turned on on the device, the PC receives the command: MAP999
1.2. When including area: MAP(number of area)1
1.3. When disabling region: MAP(number of region)0
1.4. When including the whole map: MAP001
1.5. When turning off the whole map: MAP000

2. Incoming commands:

2.1. Include the whole map: MAP001
2.2. Turn off the whole map: MAP000
2.3. Include district: MAP(number of district)1
2.4. Disable area: MAP(number of area)0
2.5. Get information about included areas: MAP999 In response to this command, data on all included areas is transmitted in the format of clause 1.2 (as if all included areas were re-included).
2.6. Get information about disabled areas: MAP995 In response to this command, data on all disabled areas is transmitted in the format of clause 1.3 (as if all disabled areas are turned off again).

When turning off the last included area, the command "turn off the entire map" should also be received.
When you include the last non-included area, the command "enable the entire map" must also be received.
The district number is ASCII digit characters (0x30-0x39).

From idea to implementation

Anticipating that it might be a rather difficult problem to manufacture our own case for the remote control, it was decided to take a ready-made remote control from a serial device. The system of IR control commands of the RC5 format was chosen as the basis of the IR control system. Currently, remote control (RC) on IR rays is very widely used to control various equipment. Perhaps the first type of household equipment that used IR remote control was televisions. Now remote control is available in most types of household audio and video equipment. Even portable music centers Recently, more and more often they are equipped with a remote control system. But Appliances this is not the only area of ​​application for remote control. Devices with remote control are quite widespread both in production and in scientific laboratories. There are quite a lot of incompatible IR remote control systems in the world. The most widely used system is the RC-5. This system is used in many televisions, including domestic ones. Currently, different factories produce several modifications of the RC-5 remote controls, and some models have quite a decent design. This allows you to get a home-made device with IR remote control at the lowest cost. Omitting the details of why this particular system was chosen, let's consider the theory of building a system based on the RC5 format.

Theory

To understand how the control system works, you need to understand what the signal at the output of the IR remote control is.

The RC-5 infrared remote control system was developed by Philips for the needs of home appliances. When we press a button on the remote control, the transmitter chip is activated and generates a sequence of pulses that have a fill frequency of 36 kHz. LEDs convert these signals into infrared radiation. The emitted signal is received by a photodiode, which again converts the IR radiation into electrical impulses. These pulses are amplified and demodulated by the receiver chip. Then they are fed to the decoder. Decoding is usually done in software by a microcontroller. We will talk about this in detail in the section on decoding. RC5 code supports 2048 commands. These teams make up 32 groups (systems) of 64 teams each. Each system is used to control specific device such as TV, VCR, etc.

At the dawn of the formation of IR control systems, the signal was formed in hardware. For this, specialized ICs were developed, and now more and more remote controls are made on the basis of a microcontroller.

One of the most common transmitter ICs is the SAA3010 IC. Let's briefly consider its characteristics.

• Supply voltage - 2 .. 7 V
• Current consumption in standby mode - no more than 10 μA
• Maximum output current - ±10 mA
• Maximum clock frequency- 450 kHz

Structural scheme The SAA3010 chip is shown in Figure 1.

Figure 1. Block diagram of the SAA3010 IC.

The description of the pins of the SAA3010 chip is given in the table:

The transmitter chip is the heart of the remote control. In practice, the same remote control can be used to control multiple devices. The transmitter chip can address 32 systems in two different modes: combined mode and single system mode. In combined mode, the system is selected first, and then the command. The selected system number (address code) is stored in special register and a command relating to that system is transmitted. Thus, to transmit any command, successive pressing of two buttons is required. This is not entirely convenient and is justified only when working simultaneously with large quantity systems. In practice, the transmitter is more often used in single system mode. In this case, instead of the matrix of system selection buttons, a jumper is mounted, which determines the system number. In this mode, only one button press is required to send any command. Using the switch, you can work with several systems. And in this case, only one button press is required to transmit the command. The transmitted command will refer to the system currently selected with the switch.

To enable the combined mode, the output of the transmitter SSM (Single System Mode) must be applied low. In this mode, the transmitter chip operates as follows: during rest, the X and Z lines of the transmitter are driven high by internal p-channel pull-up transistors. When a button is pressed in an X-DR or Z-DR matrix, the keyboard debounce cycle is initiated. If the button is closed for 18 cycles, the "generator enable" signal is fixed. At the end of the debounce cycle, the DR outputs are turned off and two scan cycles are started, turning on each DR output in turn. In the first scan cycle, the Z-address is found, in the second - the X-address. When the Z-entry (system matrix) or the X-entry (instruction matrix) is found to be in the zero state, the address is latched. When a button is pressed in the system matrix, the last command (i.e., all command bits are equal to one) is transmitted in the selected system. This command is transmitted until the system select button is released. When a button is pressed in the command matrix, the command is transmitted along with the system address stored in the latch register. If the button is released before transmission starts, a reset occurs. If the transfer has started, then regardless of the state of the button, it will be completed completely. If more than one Z or X button is pressed at the same time, the generator will not start.

To enable single system mode, the SSM pin must be high and the system address must be set with the appropriate jumper or switch. In this mode, the transmitter X-lines are in a high state during rest. At the same time, the Z-lines are turned off to prevent current consumption. In the first of two scans, the system address is determined and stored in a latch. In the second cycle, the command number is determined. This command is sent along with the system address stored in a latch. If there is no Z-DR jumper, then no codes are transmitted.

If the button was released between sending the code, then a reset occurs. If the button is released during the debounce routine or during the sensor scan, but before a button press is detected, then a reset also occurs. Outputs DR0 - DR7 have an open drain, at rest the transistors are open.

The RC-5 code has an additional control bit that is inverted each time the button is released. This bit informs the decoder whether the button is being held or a new press has occurred. The control bit is inverted only after a fully completed send. Scanning cycles are performed before each message, so even if you change the pressed button to another during the transmission of the package, the system number and commands will still be transmitted correctly.

The OSC pin is the input/output of a 1-pin oscillator and is designed to connect a ceramic resonator at a frequency of 432 kHz. In series with the resonator, it is recommended to include a resistor with a resistance of 6.8 Kom.

Test inputs TP1 and TP2 must be connected to ground during normal operation. A high logic level on TP1 increases the scan rate, and when high level on TP2 - the frequency of the shift register.

At rest, the DATA and MDATA outputs are in the Z-state. The pulse train generated by the transmitter at the MDATA output has a duty cycle of 36 kHz (1/12 of the clock frequency) with a duty cycle of 25%. The DATA output generates the same sequence, but without padding. This output is used when the transmitter chip acts as a built-in keyboard controller. The signal at the DATA output is completely identical to the signal at the output of the remote control receiver chip (but, unlike the receiver, it has no inversion). Both of these signals can be processed by the same decoder. Using the SAA3010 as a built-in keyboard controller is in some cases very convenient, since only one interrupt input is consumed by the microcontroller to poll the matrix of up to 64 buttons. Moreover, the transmitter chip allows +5 V power supply.

The transmitter generates a 14-bit data word, the format of which is:

Figure 2. Data word format of the RC-5 code.

The start bits are for setting the AGC in the receiver IC. The control bit is a sign of a new press. The clock duration is 1.778 ms. As long as the button remains pressed, the data word is transmitted at 64 clock intervals, i.e. 113.778 ms (Fig. 2).

The first two pulses are start pulses and both are logical "1s". Note that half of the bit (empty) passes before the receiver determines the real start of the message.
The extended RC5 protocol uses only 1 start bit. The S2 bit is transformed and added to the 6th command bit, making a total of 7 command bits.

The third bit is the control bit. This bit is inverted whenever a key is pressed. In this way, the receiver can distinguish between a key that remains pressed or is periodically pressed.
The next 5 bits represent the address of the IR device, which is sent with the first LSB. The address is followed by 6 command bits.
The message contains 14 bits, together with the pause, have a total duration of 25.2 ms. Sometimes the message may be shorter due to the fact that the first half of the start bit S1 is left blank. And if the last bit of the command is a logical "0", then the last part of the message bit is also empty.
If the key remains pressed, the message will be repeated every 114ms. The control bit will remain the same in all messages. This is a signal for the receiver program to interpret this as an auto-repeat function.

To ensure good noise immunity, two-phase coding is used (Fig. 3).

Figure 3. Coding "0" and "1" in the RC-5 code.

When using the RC-5 code, it may be necessary to calculate the average current draw. This is quite easy to do if you use Fig. 4, which shows the detailed structure of the package.

Figure 4. Detailed structure of the RC-5 package.

To ensure that the equipment responds equally to RC-5 commands, the codes are distributed in a very specific way. This standardization allows you to design transmitters that allow you to control various devices. With the same command codes for the same functions in different devices a transmitter with a relatively small number of buttons can simultaneously control, for example, an audio complex, a TV and a VCR.

System numbers for some household appliances are listed below:

0 - TV
2 - Teletext
3 - Video data
4 - Video player (VLP)
5 - Video Cassette Recorder (VCR)
8 - Video tuner (Sat.TV)
9 - Camcorder
16 - Audio preamplifier
17 - Tuner
18 - Tape recorder
20 - Compact player (CD)
21 - Turntable (LP)
29 - Lighting

The remaining system numbers are reserved for future standardization or experimental use. The correspondence of some command codes and functions has also been standardized.
Command codes for some functions are given below:

0-9 - Numerical values ​​0-9
12 - Standby mode
15 - Display
13-mute
16 - volume +
17 - volume -
30 - search ahead
31 - search back
45 - ejection
48 - pause
50 - rewind
51 - fast forward
53 - playback
54 - stop
55 - entry

In order to build a complete IR remote control based on the transmitter chip, you also need an LED driver that is capable of providing a large pulse current. Modern LEDs operate in remote controls at pulsed currents of about 1 A. It is very convenient to build an LED driver on a low-threshold (logic level) MOSFET, for example, KP505A. An example of a circuit diagram of the console is shown in fig. 5.

Figure 5. Schematic diagram of the RC-5 console.

The system number is set by a jumper between pins Zi and DRj. The system number will then be:

The command code that will be transmitted when a button is pressed that closes the Xi line with the DRj line is calculated as follows:

The IR remote control receiver must recover data with bi-phase encoding, it must respond to large, rapid changes in signal level, regardless of interference. The pulse width at the receiver output should differ from the nominal value by no more than 10%. The receiver must be insensitive to constant external illumination. Satisfying all these requirements is not easy. Old implementations of the IR remote control receiver, even with the use of specialized microcircuits, contained dozens of components. These receivers are often used resonant circuits tuned to 36 kHz. All this made the design difficult to manufacture and adjust, and required the use of good shielding. Recently, three-pin integrated IR remote control receivers have become widespread. In one package, they combine a photodiode, a preamplifier and a shaper. At the output, a regular TTL signal is formed without filling 36 kHz, suitable for further processing by the microcontroller. Such receivers are manufactured by many companies, these are SFH-506 from Siemens, TFMS5360 from Temic, ILM5360 from Integral and others. At present, there are also more miniature versions of such microcircuits. Since there are other standards besides RC-5 that differ, in particular, in the duty cycle, there are integrated receivers for different frequencies. To work with the RC-5 code, you should choose models designed for a duty cycle of 36 kHz.

As an IR remote control receiver, you can also use a photodiode with an amplifier-shaper, which can serve as a specialized microcircuit KR1568KhL2. A diagram of such a receiver is shown in Figure 6.

Figure 6. Receiver on the KR1568HL2 chip.

For the information display control system, I chose an integrated IR remote control receiver. A highly sensitive PIN photodiode is installed as an optical radiation receiver in the TSOP1736 microcircuit, the signal from which is fed to the input amplifier, which converts the output current of the photodiode into voltage. The converted signal is fed to an amplifier with AGC and then to a bandpass filter, which separates signals with an operating frequency of 36 kHz from noise and interference. The selected signal is fed to the demodulator, which consists of a detector and an integrator. In the pauses between pulses, the AGC system is calibrated. This is controlled by the control scheme. Thanks to this construction, the microcircuit does not respond to continuous interference even at the operating frequency. The active level of the output signal is low. The microcircuit does not require the installation of any external elements. All its components, including the photodetector, are protected from external interference by an internal electric screen and are filled with special plastic. This plastic is a filter that cuts off optical interference in the visible light range. Thanks to all these measures, the microcircuit is characterized by a very high sensitivity and a low probability of false signals. However, integrated receivers are very sensitive to power noise, so it is always recommended to use filters such as RC. Appearance integrated photodetector and the location of the conclusions are shown in fig. 7.

Figure 7. Integrated receiver RC-5.

RC-5 decoding

Since the basis of our device is the PIC18F252 microcontroller, we will decode the RC-5 code in software. The RC5 code reception algorithms offered on the network are mostly not suitable for real-time devices, such as our device. Most of the proposed algorithms use software cycles to generate time delays and measurement intervals. This is not suitable for our case. It was decided to use interrupts on the fall of the signal at the INT input of the PIC18F252 microcontroller, measure the time parameters using TMR0 of the PIC18F252 microcontroller, the same timer generates an interrupt when the next pulse timeout has expired, i.e. when there is a pause between two messages. The demodulated signal from the output of the DA1 microcircuit is fed to the INT0 input of the microcontroller, in which it is decoded and the decoded command is issued to shift registers for key management. The decryption algorithm is based on measuring the time intervals between interrupts of the PIC18F252 microcontroller. If you look closely at Figure 8, you can see some features. So if the interval between interrupts of the PIC18F252 microcontroller was equal to 2T, where T is the duration of a single RC5 pulse, then the received bit can be 0 or 1. It all depends on which bit was before. In the program below with detailed comments, this is very clearly visible. The entire project is available for download and use for personal purposes. When reprinting a link is required.

Integrated receivers of infrared radiation are widely used in household radio-electronic equipment. In another way, they are also called IR modules.

They can be found in any electronic device which can be controlled by the remote control.

Here, for example, is the IR receiver on the printed circuit board of the TV.

Despite the apparent simplicity of this electronic component, it is a specialized integrated circuit designed to receive an infrared signal from remote controls (RC). As a rule, an IR receiver has at least 3 pins. One pin is common and connects to minus «-» food ( GND), the other serves as a positive «+» output ( Vs), and the third output of the received signal ( Out).

Unlike a conventional infrared photodiode, an IR receiver can receive and process an infrared signal, which is an IR pulse of a fixed frequency and a certain duration - a burst of pulses. This technological solution eliminates random triggers that can be caused by background radiation and interference from other devices emitting in the infrared range.

For example, fluorescent lighting lamps with electronic ballast can create strong interference to the IR receiver. It is clear that using an IR receiver instead of a conventional IR photodiode will not work, because the IR module is a specialized microcircuit, sharpened for certain needs.

In order to understand the principle of operation of the IR module, let's take a closer look at its device using a block diagram.

The IR receiver chip includes:

PIN photodiode

Adjustable Amplifier

Band pass filter

Amplitude detector

Integrating filter

threshold device

PIN photodiode- This is a kind of photodiode, in which between areas n and p there is a region of intrinsic semiconductor ( i-area ). The intrinsic semiconductor region is essentially a layer of pure semiconductor without impurities introduced into it. It is this layer that gives the PIN diode its special properties. By the way, PIN diodes (not photodiodes) are actively used in microwave electronics. Take a look at your mobile phone, it also uses a PIN diode.

But, back to the PIN photodiode. V normal state no current flows through the PIN photodiode, since it is included in the circuit in the opposite direction (in the so-called reverse bias). Since under the action of external infrared radiation in i-regions electron-hole pairs appear, then as a result, a current begins to flow through the diode. This current is then converted into voltage and fed to adjustable amplifier.

Further signal from variable amplifier goes to bandpass filter. It serves as protection against interference. The bandpass filter is tuned to a certain frequency. So in IR receivers, band-pass filters are mainly used, tuned to a frequency of 30; 33; 36; 36.7; 38; 40; 56 and 455 kilohertz. In order for the signal emitted by the remote control to be received by the IR receiver, it must be modulated with the same frequency as the band pass filter of the IR receiver. This is how, for example, a modulated signal from an emitting infrared diode looks like (see figure).

And this is how the signal at the output of the IR receiver looks like.

It should be noted that the selectivity of the bandpass filter is low. Therefore, an IR module with a 30 kHz filter may well receive a signal with a frequency of 36.7 kHz or more. True, at the same time, the distance of confident reception is noticeably reduced.

After the signal has passed through the band-pass filter, it is sent to amplitude detector and integrating filter. An integrating filter is needed to suppress short single signal bursts that can be caused by interference. The signal is then sent to threshold device and then on output transistor.

For stable operation of the receiver, the gain of the adjustable amplifier is controlled by the automatic gain control system ( AGC). Since the useful signal is a burst of pulses of a certain duration, due to the inertia of the AGC, the signal has time to pass through the amplification path and other nodes of the circuit.

In the case when the duration of the burst of pulses is excessive, the AGC system is triggered, and the receiver stops receiving the signal. This situation can occur when the IR receiver is exposed fluorescent lamp with electronic ballast, which operates at frequencies of 30 - 50 kilohertz. In this case, the modulated infrared radiation from the mercury vapor of the lamp can pass through the protective band-pass filter of the photodetector and trigger the AGC. Naturally, in this case, the sensitivity of the IR receiver drops.

Therefore, do not be surprised when the TV's photodetector does not receive commands from the remote control. Perhaps he is simply hindered by the illumination of fluorescent lamps.

Automatic threshold adjustment ( ARP) performs a similar function as the AGC, controlling the threshold of the threshold device. The ARP sets the threshold level in such a way as to reduce the number of false pulses at the output of the module. In the absence of a useful signal, the number of false pulses can reach 15 per minute.

The shape of the IR module body contributes to focusing the received radiation on the sensitive surface of the photodiode. The body material transmits radiation with a wavelength of 830 to 1100 nm. Thus, the device implements an optical filter. An electrostatic screen is installed in the module to protect the receiver elements from the effects of external electric fields. The photo shows the IR modules of the brand HS0038A2 and TSOP2236. For comparison, conventional IR photodiodes are shown next to each other. KDF-111V and FD-265.

IR receivers

How to check the health of the IR receiver?

Since the IR signal receiver is a specialized microcircuit, in order to reliably check its serviceability, it is necessary to apply a supply voltage to the microcircuit. For example, the nominal supply voltage for the "high voltage" IR modules of the TSOP22 series is 5 volts. The current consumption is units of milliamps (0.4 - 1.5 mA). When connecting power to the module, it is worth considering the pinout.

In the state when no signal is applied to the receiver, as well as in the pauses between bursts of pulses, the voltage at its output (without load) is almost equal to the supply voltage. Output voltage between ground (GND) and the signal output pin can be measured with a digital multimeter. You can also measure the current consumed by the module. If the current consumption exceeds the typical, then most likely the module is faulty.

Read how to check the health of the IR receiver using the power supply, multimeter and remote control.

As you can see, the IR signal receivers used in infrared remote control systems have a rather sophisticated device. These photodetectors are often used in their homemade devices microcontroller enthusiasts.