Remote control systems that use infrared (IR) communication require an IR decoder IC to receive and interpret the modulated IR signals from the remote control. The IR decoder plays a crucial role in the overall functionality of appliance and electronics remote controls. This article provides an overview of IR decoder ICs, their working mechanism and key parameters to consider when selecting these components.
What is an IR Decoder IC?
An IR decoder IC (integrated circuit) is a special purpose chip designed to receive and decode modulated infrared signals transmitted by a remote control. It converts the IR pulses into electrical signals that can be processed by a microcontroller or other control circuitry.
Some key characteristics of IR decoder ICs:
- They contain a photodiode to detect the IR pulses and amplifier circuits to boost the signal.
- They filter and demodulate the received signal to extract the encoded binary data.
- They provide digital outputs corresponding to the received code for further processing.
- Common packaging styles include DIP, SOIC, PDIP, TSOP.
- Low power consumption, high sensitivity and noise immunity are important parameters.
Fig 1. Simplified internal block diagram of an IR decoder IC.
How IR Decoders Work
An IR decoder IC works in the following manner to decode the modulated infrared beams:
- Signal Reception – The IR photodiode receives the pulsating IR beam and converts it into an analog electrical signal. The received signal strength is very low, typically in microvolts.
- Preamplification – The input preamplifier stage amplifies the weak photodiode output to improve the signal to noise ratio. This allows reliable detection of pulses.
- Bandpass Filtering – Bandpass filters remove low and high frequency noise from the amplified signal, leaving just the frequency components of interest.
- Demodulation – A demodulator extracts the encoded binary pattern from the filtered signal based on the modulation scheme used. Common schemes are Pulse Code Modulation (PCM) and Pulse Width Modulation (PWM).
- Wave Shaping – The demodulated signal is further shaped into well-defined digital waveforms using schmitt triggers and pulse shapers.
- Decoder – A decoder logic verifies the received binary pattern against protocol specifications. Valid data is converted into electrical signals like clock, address and command bits.
- Outputs – The extracted control data is available on digital output pins of the IC for interfacing with a microcontroller or other external circuits.
Proper signal reception and conditioning is critical for the IR decoder to reliably recover the transmitted control codes under varying conditions. The key internal blocks are carefully designed to achieve good sensitivity, noise immunity and detection range in IR systems.
Key Parameters of IR Decoder ICs
When selecting an IR decoder IC for a particular application, some important parameters need to be considered:
- Carrier Frequency – Frequency of modulated IR signal it can decode. Most ICs support common frequencies between 30-60kHz.
- Encoding Schemes – Modulation formats like PCM, PWM, etc. the IC is compatible with.
- Code Formats – Number of address and command bits supported that match remote control.
- Supply Voltage – Power supply voltage range of the IC. Common levels are 3-5V, with lower better for battery operation.
- Standby Current – Quiescent current drawn by the IC to minimize power consumption.
- Active Current – Current drawn during signal reception and decoding operations.
- Reception Range – Maximum distance from which remote signals can be detected. Longer the better for usability.
- Output Configuration – Digital output styles like push-pull or open drain compatible with microcontroller.
- Output Logic – Logic voltage levels on digital output pins – CMOS, TTL etc.
- Ambient Light Immunity – Resistance to false triggering under ambient indoor/outdoor lighting.
- EMI/EMC Immunity – Rejection of electromagnetic interference for noise-free operation.
- Operating Temperature – Allowable temperature range based on application environment. Industrial grade ICs operate from -40°C to +85°C.
- Packaging Style – IC packaging e.g. DIP, SOIC, TSOP etc. suited for production and handling processes.
The datasheet of the IR decoder provides these key specifications along with application circuits to guide the design.
Common IR Decoder ICs
Some examples of widely used IR decoder integrated circuits are:
- TSOP1738 – A very common and low cost 38kHz IR receiver series in PDIP/SOIC packages.
- Vishay TSOP312..TSOP344 – High sensitivity IR receiver series with PCM/PWM decoding.
- Vishay TSSP4..TSSP6 – Industrial grade IR decoders with extended temperature range.
- Rohm RU11..RU18 Series – Low power decoders with detection range up to 10m.
- Panasonic PNA4602 – 36kHz capable decoder with CMOS push-pull outputs.
- Sharp GP1U52X – Wide reception angle and automatic ambient light compensation.
- Samsung KSX1001 – Multi-protocol decoder supporting RC5/RC6/NEC codes.
- Everlight ALS-PT19..ALS-PT29 – Miniature SMD package decoders with PWM decoding.
- Vishay IRT-M 0020..IRT-M 0036 – TSOP package decoders tuned for different carrier frequencies.
- Osram SFH 51..SFH 57 – Industrial grade, moisture resistant IR receiver modules.
This covers the most commonly used IR decoder series – both general purpose and application specific. When designing a remote control receiving circuit, refer to the technical specs to pick an appropriate decoder IC tailored to the requirements.
Interfacing IR Decoder to Microcontrollers
The task of the IR decoder IC is to recover the modulated IR remote control signals and extract the encoded data. This data is made available on digital outputs that can be interfaced to a microcontroller for further processing.
Here are some methods for connecting IR decoder outputs to microcontrollers:
- Parallel Interface – Each digital output bit of the decoder like address, command, valid transmission etc. is connected separately to GPIO pins of the microcontroller. This allows direct monitoring of the control data.
- Serial Interface – The output bits are sent serially from the decoder to the microcontroller through a common data line. Fewer connections needed but added software complexity.
- I²C Interface – The IR decoder is configured as an I²C slave device while the microcontroller acts as master. Only two bus lines SCL and SDA needed for communication.
- SPI Interface – The SPI bus is used where microcontroller is master and the decoder is the slave. Data is exchanged using MOSI, MISO, SCK and SS lines.
- USB Interface – For direct connection to host PCs, the IR decoder output data is transmitted over USB. Requires USB controller hardware.
- Interrupt Interface – The decoder INT or MATCH output can be tied to a microcontroller interrupt pin to trigger code execution on new data reception.
So in summary, the IR decoder IC provides electrical outputs that correspond to the received IR remote codes. These outputs can be interfaced using parallel, serial or bus connections for further decoding in firmware.
Typical Application Circuit
Here is a typical application circuit using an IR decoder IC:
Fig 2. Example schematic with IR decoder connected to a microcontroller.
It shows how just a few components are needed around the decoder IC to receive and process remote control signals:
- IR photodiode and preamplifier convert received IR light into electrical signal.
- Capacitors provide power supply filtering.
- Current limiting resistor for the IR LED.
- Digital outputs connect to a microcontroller for further decoding and control.
- Minimal external components make IR decoders cost-effective and simple to implement.
With this basic circuit, IR signals from common remote controls can be captured and processed. The microcontroller code can be customized to perform required control actions based on the received commands.
Remote Control Receiver Design Considerations
Some important aspects to factor in when incorporating an IR decoder IC into a remote control receiver design are:
- Select a decoder IC that matches the modulation frequency, encoding scheme and code formats used by the remote control.
- Determine the required reception range based on usage environment. Longer range decoders or photodiode lenses may be needed.
- Ensure the decoder IC has suitable immunity against ambient interference – sunlight, fluorescent lights etc. Use ICs with automatic filtered IR carrier detection if needed.
- Place the IR receiver diode properly oriented towards the area where remote is aimed from. Avoid obstructions in line-of-sight.
- Add plastic pouches or tubes around photodiode to limit interference from indirect multi-path IR reflections.
- Where multiple devices need individual control, use decoder ICs capable of decoding unique address codes.
- For outdoor usage, ensure the IR receivers and circuits have adequate waterproofing and surge protection.
- Properly decode the serial or parallel data outputs from the IR receiver through microcontroller code or external logic.
By carefully selecting IR decoder ICs matched to the remote control codes and appropriately integrating them into product designs, robust IR wireless control systems can be developed.
Advantages of IR Decoder ICs
Some key benefits of using dedicated IR decoder integrated circuits are:
- Simplified Design – Complete decoders in compact, easy to use IC package. Avoid complex discrete component circuits.
- Low Cost – Economical compared to individual photodiodes, amplifiers, filters and demodulators.
- Low Power – Optimized for low current consumption in battery powered remotes.
- High Sensitivity – Inbuilt amplification and conditioning provides excellent reception range and noise immunity.
- Standard Compliant – Support widespread modulation standards like RC5, NEC IR, RC6 etc.
- Reliable Decoding – Recover encoded data accurately with low bit error rates.
- Immunity to Noise – Effectively suppress interference from ambient light and EM sources.
- Compact Footprint – Small TSOP, SOIC packages fit easily on densely packed PCBs.
- Minimal Components – Require few external passive components and connections.
Overall, IR decoder ICs enable building high performance and cost-effective wireless remote control receiving circuits. Combined with a microcontroller, they offer a complete solution for reliable IR communication in consumer electronics systems.
Frequently Asked Questions
Here are some common FAQs about IR decoder ICs:
Q: What is the difference between IR transmitter and receiver ICs?
A: IR transmitters take digital control data and modulate it into encoded IR light pulses. IR receivers like decoders detect these pulses and extract the original digital data. Transmitters and receivers work in pair for two-way IR remote communications.
Q: Can IR signals pass through solid objects?
A: No, IR signals require direct line-of-sight for transmission and reception. They cannot penetrate through walls or solid enclosures. However, IR can reflect off surfaces to allow non-line-of-sight operation to some extent.
Q: How is distance and tight radiation pattern achieved in IR remotes?
A: IR LEDs with integral lens caps and higher power levels help achieve longer range transmission concentrated in a tight beam. IR photodiode lenses help focus received signals for better reception.
Q: What interfaces are commonly used to connect IR decoder ICs?
A: Parallel, serial (UART), I2C and SPI are some standard interfaces used to send decoder data to external MCUs and processors.
Q: Can IR remotes control multiple devices separately?
A: Yes, by using unique address codes assigned to each device. The IR decoder distinguishes which device to control based on the address.
Q: What happens if multiple remotes are used together?
A: IR systems are inherently designed to prevent interference between signals of multiple remotes. Unique encoding patterns and transmission protocols avoid cross-activation.
Q: Can IR remote systems be susceptible to hacking?
A: Basic IR remotes have minimal security risks due to the need for line-of-sight access. However, more advanced bidirectional IR systems do incorporate encryption to prevent such risks.
Q: What is the typical range of IR remotes?
A: Short range remotes typically work upto 10 feet while long range versions can reach up to 30 feet. Range depends on transmitter power, reception angle and ambient conditions.
IR decoder ICs are indispensable components that enable reliable and low-cost remote control functionality in modern appliances and devices. Their ability to accurately receive IR signals under varying conditions, extract control data and interface with external MCUs has made them the standard building block for IR receivers. With a good understanding of the working, specifications and interfaces of decoder ICs, engineers can easily implement robust wireless control in their products using proven infrared technology.