Infrared (IR) communication technologies are probably one of the most influential, yet also one of the least flashiest. The fact that IR communication tends to be highly directional and often limited to low data rate leads many people to scoff at it, deeming it barely worthy of more than making TV remotes work, perhaps along with some unloved industrial gear like the IR interface of electrical meters.

This is a shame, because TV remotes are a good example of why sometimes you want something that is directional, and anyone who has battled with Bluetooth pairing can attest to the value of things simply working by pointing it at the device. IR protocols also have the advantage of inherent privacy protection as walls and other obstacles will block the signal, unlike that of an exploitable Bluetooth device which happily advertises to your neighbors and passersby.

For reasons like the above – as well as their simplicity and hackability – IR protocols are worthy of a detailed look.

Remote Control

Naturally, one of the oldest uses of consumer IR protocols is that of the venerable IR remote control. Initially TVs used wired and ultrasonic remote controls, with the latter using simple ultrasonic tones to transfer a command, but with IR protocols and the advent of cheap MCUs it became possible to create extensive communication protocols. Of these the NEC, Sony IR (SIRC) and Philips protocols are probably the most well-known and most used.

These use an approximately 38 kHz carrier, with the common NEC protocol using pulse distance encoding – a form of amplitude-shift keying – and the Philips RC-5 protocol using Manchester encoding. Within this encoding, these protocols define various bit fields and other values that can be used by a receiver to determine whether it’s being targeted, and if so what command the user wishes to have performed.

When it comes to those cheap-and-cheerful remotes that you get with just about any RGB light strip and others gadgets these days, they tend to use the same NEC protocol, with many MCU-based projects around that can control these gadgets directly with a simple IR LED.

This STM32F0-based project by [eleksaggr] on GitHub that targets the common 24-key RGB remotes. This Infrared Remote Control Implementation application note by Texas Instruments for the MSP430, which contains a good overview of the modulation and encoding schemes, as well as how to implement a remote control.

Many smartphones have – or used to have – an IR blaster feature that can target the same carrier frequency and a range of protocols to control just about anything that is IR remote controlled. In a world of smartphones this would theoretically mean that everyone has a universal remote in their pocket at any time, if it wasn’t for IR blasters becoming pretty rare. If your recently purchased smartphone still has an IR blaster, it’s very likely a Chinese brand, which is a shame as IR remotes are still used for so many things.

IrDA

Of course, IR remotes are quite a specific use case, but you can send a lot more than just a basic set of commands to a device. The most well-known standard here is IrDA, which stands for Infrared Data Association, the association which defined the various standards.

The basic principles behind IrDA remain effectively the same as with the remote control protocols, just designed to be capable of far higher transfer speeds. This is accomplished through various types of encoding, modulation and other techniques also observed with non-IR forms of wireless communication. Using this a range of speeds are possible, defined as:

• SIR (115 kbit/s).
• MIR (1 Mbit/s).
• FIR (4 Mbit/s).
• VFIR (16 Mb/s).
• UFIR (96 Mbit/s).
• Giga-IR (512 Mbit/s – 1 Gbit/s).

In additional a range of derived protocols exist such as IrSimple that allows for easy sharing of images between phones, printers, and displays. All of this uses generally the same IrDA software stack, though the special versions such as IrSimple optimize it to make transfers take less than a second for a 500 kB picture.

All communication generally happens in half-duplex, as the sending side tends to produce too much interference for the receiving side of the transceiver to reliably receive data. Distance between the two sides can be as much as two meters, though the lower power versions shrink that down to 20 cm or thereabouts.

Within this range of speeds you can pick whatever the device needs. Power meters, for instance, are plenty happy with the IrDA-SIR protocol, which is low-power and speed enough to bitbang on even a basic MCU in these meters with just a basic IR transceiver attached to its pins.

Power Meters

The humble power meter that lurks in your utility closet or wherever else it is installed has to be shielded from whatever environment it is installed in, ergo they require some kind of low-power, low-speed wireless interface. Using nothing but an IR-transparent window on the enclosure it is then possible for a read-out device to be pressed up to said window, where it’ll quickly query the device for the necessary information.

This same feature is also found on heat meters and other types of devices where such basic read-out functionality is required. Here security is managed by not only the short-distance, line-of-sight requirement of an IR communication link, but also by having a sign-on involving an encrypted password exchange.

Although IrDA-SIR was commonly used here, these days DLMS/COSEM, also known as IEC 62056 is much more common. While radio-based forms of automatic meter reading (AMR) are also used, short-range protocols like this have a definite privacy advantage, with the line-of-sight feature meaning that the reader has to be literally in front of the meter to work, unlike with RF wireless approaches.

Whether this privacy aspect is important depends on the situation, but it’s hard to argue with the low power requirements compared to stuffing a Bluetooth or Wi-Fi module into the meter and dealing with its implications.

Game Consoles

Although it may seem that handheld game consoles went straight from the Game Boy’s link cable to Wi-Fi transfers on the Nintendo 3DS beyond, it featured an IR communication port. This was intended to support peripherals like the Circle Pad Pro and the Amiibo reader/writer device for the original 3DS as it did not feature the NFC reader of the New Nintendo 3DS.

As it turns out, the 3DS uses irDA-SIR for this expansion feature, with e.g. the Circle Pad Pro using a 96000 baud rate. Since this peripheral merely is there to add a second circle pad to match the built-in left one, it doesn’t need a lot of bandwidth.

In the case of the external NFC reader, this was a similar low bandwidth application where it made a lot of sense to use this same IR port to provide this new feature to older 3DS consoles, instead of making it a New 3DS-exclusive feature. Although one could have used Bluetooth for this even back then, the 3DS console did not include Bluetooth, and when looking at e.g. the Joycons of the Nintendo Switch it’s clear that they are a tad more power hungry and complex circuitry-wise.

When low-power and line-of-sight are benefits rather than a potential source of confusion of which peripheral you’re trying to pair with, it can make a lot of sense.

DIY IR Transceiver

If you’re feeling like making your own IR receiver, receiver or even transceiver solution, there are many options. Perhaps the most exciting aspect is that even if you want to use something like IrDA, this feature is often part of the UART in many MCUs. In the case of Espressif’s ESP32 MCUs, for example, you can look at its list of potential UART modes and note that you can pick IrDA as well as RS485 in addition to plain UART functionality.

There are also dedicated IrDA encoder/decoder ICs, such as the MCP2120. This gets you IrDA-SIR support for any UART interface that does not directly implement this protocol. You can also use something like the Vishay TFDU4101 IrDA transceiver that integrates everything including the IR elements into a single package.

If you’re more about messing with NEC, Sony and Philips remote control protocols, then a common part like the VS1838b provides a similar solution to the Vishay part for 38 kHz applications. This IR receiver handles all the receiving, demodulating, amplification and other tasks, leaving it to the receiving MCU to parse the received data.

This of course just barely scratches the surface of everything IR communication-related, so feel free to chime in with your own info dumps and requests for additional topics to cover.