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13. IR Remote Control User Guide

13.1. Introduction to Infrared Transmission

Users can request the sample codes of infrared transmission by sending an e-mail to

feedback@espressif.com.

This document introduces how to implement transmitting or receiving remote control codes

using the 32-bit NEC IR transmission protocol as an example.

13.1.1. Transmitting

Users can use the following methods to transmit carrier wave:

•

BCK of I2S

•

38KHz carrier frequency generated by WS pin

•

Carrier wave generated by any GPIO via sigma-delta function. However, the duty ratio

of carrier wave generated by sigma-delta is around 20%, thus MTMS pin (GPIO14) is

suggested, for this pin can generate standard square wave at a carrier frequency of

38KHz and a duty ratio of 50% exactly.

In the sample codes, data transmission queue is generated via the DSR TIMER interface of

system FRC2, while a state machine driving the transmission of infrared data is also

generated.

Considering that the timing precision of transmitting NEC infrared code should reach a level

of µs, when initiating IR TX, system_timer_reinit should be invoked to improve the timing

precision of FRC2. In user_conﬁg.h, enable the deﬁnition of USE_US_TIMER, then interface

function os_timer_arm_us can be invoked to implement precise timing at the level of µs.

13.1.2. Receiving

The receiving of remote control codes is implemented via edge-triggered interrupt. When

one system is substracted from one another, the result is the duration time of the wave.

This can be processed by software state machine ir_intr_handler.

⚠ Notice:

• Receiving of infrared remote control codes is implemented via GPIO interrupt. However, the system

can only register only one IO interrupt handler program at the same time. If other IOs also need

interrupts, please handle these interrupts in the same processing program by determine the source of

interrupt and deal with them accordingly.

•

In non-OS version of SDK, functions with ICACHE_FLASH_ATTR properties, including print function

os_printf deﬁned in IROM section of the Flash, should NOT be invoked in the whole process of

interrupt handling process such as GPIO, UART, FRC, etc.

Espressif

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2017.05

ESP8266 Datasheet(PDF) 103 Page - ESPRESSIF SYSTEMS (SHANGHAI) CO., LTD.