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https://github.com/peterhinch/micropython_ir

Nonblocking device drivers to receive from IR remotes and for IR "blaster" apps.
https://github.com/peterhinch/micropython_ir

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Nonblocking device drivers to receive from IR remotes and for IR "blaster" apps.

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README 

        
# Device drivers for IR (infra red) remote controls



This repo provides a driver to receive from IR (infra red) remote controls and

a driver for IR "blaster" apps. The device drivers are nonblocking. They do not

require `uasyncio` but are compatible with it, and are designed for standard

firmware builds.



The receiver is cross platform and has been tested on Pyboard, ESP8266, ESP32

and Raspberry Pi Pico.



In a typical use case the receiver is employed at the REPL to sniff the address

and data values associated with buttons on a remote control. The transmitter is

then used in an application to send those codes, emulating the remote control.



Other use cases involve running the receiver in an application. This enables an

IR remote to control a device such as a robot. This may be problematic on some

platforms. Please see [section 4](./README.md#4-receiver-limitations).



## Raspberry Pi Pico note



Early firmware has [this issue](https://github.com/micropython/micropython/issues/6866)

affecting USB communication with some PC's. This is now fixed. Please ensure

you are using up to date firmware.



#### [Receiver docs](./RECEIVER.md)



The transmitter driver is compatible with Pyboard (1.x and D series) and ESP32.

ESP8266 is unsupported; it seems incapable of generating the required signals.



#### [Transmitter docs](./TRANSMITTER.md)



# 1. IR communication



IR communication uses a carrier frequency to pulse the IR source. Modulation

takes the form of OOK (on-off keying). There are multiple protocols and at

least three options for carrier frequency: 36, 38 and 40KHz.



In the case of the transmitter the carrier frequency is a runtime parameter:

any value may be specified. The receiver uses a hardware demodulator which

should be purchased for the correct frequency. The receiver device driver sees

the demodulated signal and is hence carrier frequency agnostic.



Remotes transmit an address and a data byte, plus in some cases an extra value.

The address denotes the physical device being controlled. The data defines the

button on the remote. Provision usually exists for differentiating between a

button repeatedly pressed and one which is held down; the mechanism is protocol

dependent.



# 2. Supported protocols



The drivers support NEC and Sony protocols plus two Philips protocols, namely

RC-5 and RC-6 mode 0. There is also support for the OrtekMCE protocol used on

VRC-1100 remotes. These originally supported Microsoft Media Center but can be

used to control Kodi and (with a suitable receiver) to emulate a PC keyboard.

The Samsung protocol (NEC variant) is also supported.



Examining waveforms from various remote controls it is evident that numerous

protocols exist. Some are doubtless proprietary and undocumented. The supported

protocols are those for which I managed to locate documentation. My preference

is for the NEC version. It has conservative timing and good provision for error

detection. RC-5 has limited error detection, and RC-6 mode 0 has rather fast

timing.



A remote using the NEC protocol is [this one](https://www.adafruit.com/products/389).



# 3. Hardware Requirements



These are discussed in detail in the relevant docs; the following provides an

overview.



The receiver is cross-platform. It requires an IR receiver chip to demodulate

the carrier. The chip must be selected for the frequency in use by the remote.

For 38KHz devices a receiver chip such as the Vishay TSOP4838 or the

[adafruit one](https://www.adafruit.com/products/157) is required. This

demodulates the 38KHz IR pulses and passes the demodulated pulse train to the

microcontroller.



In my testing a 38KHz demodulator worked with 36KHz and 40KHz remotes, but this

is obviously neither guaranteed nor optimal.



The transmitter requires a Pyboard 1.x (not Lite), a Pyboard D, an ESP32 or

Raspberry Pico (RP2). Output is via an IR LED which will need a transistor to

provide sufficient current.



## 3.1 Carrier frequencies



These are as follows. The Panasonic remote appears to use a proprietary

protocol and is not supported by these drivers.



| Protocol  | F KHz | How found     | Support |

|:---------:|:-----:|:-------------:|:-------:|

| NEC       | 38    | Measured      | Y       |

| RC-5 RC-6 | 36    | Spec/measured | Y       |

| Sony      | 40    | Spec/measured | Y       |

| MCE       | 38    | Measured      | Y       | 

| Samsung   | 38    | Measured      | Y       |

| Panasonic | 36.3  | Measured      | N       |



# 4. Receiver limitations



The receiver uses a pin interrupt and depends on a quick response to a state

change on the pin. This is guaranteed on platforms which support hard IRQ's

such as the Pyboard and the RP4 Pico. The ESP32 and ESP8266 only support soft

IRQ's. This means that, if code such as WiFi communication is running

concurrently, reliable reception may be problematic.



# 5. References



Sources of information about IR protocols. The `sbprojects.net` site is an

excellent resource.  

[General information about IR](https://www.sbprojects.net/knowledge/ir/)



Also [IRMP](https://www.mikrocontroller.net/articles/IRMP_-_english)



The NEC protocol:  

[altium](http://techdocs.altium.com/display/FPGA/NEC+Infrared+Transmission+Protocol)  

[circuitvalley](http://www.circuitvalley.com/2013/09/nec-protocol-ir-infrared-remote-control.html)  

[sbprojects.net](https://www.sbprojects.net/knowledge/ir/nec.php)



The Samsung protocol:  

[Rustic Engineering](https://rusticengineering.wordpress.com/2011/02/09/infrared-room-control-with-samsung-ir-protocol/)  

[TechDesign Electronics](https://www.techdesign.be/projects/011/011_waves.htm) Waveforms of various protocols.  



Philips protocols:  

[RC5 Wikipedia](https://en.wikipedia.org/wiki/RC-5)  

[RC5 sbprojects.net](https://www.sbprojects.net/knowledge/ir/rc5.php)  

[RC6 sbprojects.net](https://www.sbprojects.net/knowledge/ir/rc6.php)



Sony protocol:  

[SIRC sbprojects.net](https://www.sbprojects.net/knowledge/ir/sirc.php)



MCE protocol:  

[OrtekMCE](http://www.hifi-remote.com/johnsfine/DecodeIR.html#OrtekMCE)



IR decoders (C sourcecode):  

[in the Linux kernel](https://github.com/torvalds/linux/tree/master/drivers/media/rc)



Interesting summary of IR protools (with thanks to Martin Bless):  

[IRMP](https://www.mikrocontroller.net/articles/IRMP_-_english#IR_Protocols)