Learning IR Remote with BLE Interface

Leonid Blouvshtein and Yosi Roitman

Introduction

This work demonstrates how to use the cc2650 device for recording and transmitting IR signals of IR remote controllers.

We support two basic actions:

• Recording - storing the next IR message.
• Transmitting - transmitting the last recorded message.

The commands are sent over BLE using a GATT profile. The BLE implementation is based on the project-zero example (supplied by TI).

Infrared Controllers - Background

A good and simple explanation can be found here.

Because there are many IR protocols and we want to support all of them, we do not interpret the IR code. We just save the timestamps of the neg/pos edge events.

Prerequisites

We will use the following components:

• CC2650 LAUNCHXL board

• BLE-Stack

• TI-RTOS 2.18

• IR Receiver connected to the cc2650 board. The IR Receiver output pin should be connected to DIO21(Check).

• The following circuit connected to the cc2650 board.

  Note: The OutPin is connected to the DIO15 pin.

Implementation Details

Recording

During the recording stage an interrupt is registered on both edges of the IR receiver pin. The interrupt saves the timestamp of the event to memory.

The timestamp is 32 bits long so for memory utilization we save only the delta from the previous event using 2 bytes.

Transmitting

We need to modulate the pulses with a 38KHz signal. For that purpose we configured a GPT in the cc2650 to function as a PWM. The GPT is turned on and off according to the pulse recorded widths.

Note that the IR LED ideally needs 50mA of current which the board cannot supply, hence we used a BJT transistor in our circuit.

Code Structure

• message.h - The message data type.
• recorder.h - The recorder that registers interrupt handlers for the receiver and records messages.
• message_printer.h - Used for debugging. Messages can be sent to the printer mailbox. A task that pends on the mailbox then prints the messages to the console.
• message_sender.h - Messages can be sent to the sender mailbox. A task that pends on the mailbox then transmits the recorded message using the IR LED.
• main.h - The main configuration of the project. Contains constants such as the IR modulated frequency, variables such as the PIN table initialization and more.

Example signals

We recorded multiple button presses of a remote control used for controlling an air conditioner.

Here we can see that the remote uses a protocol sends pulses of lengths 1, 2, 3, 4 milliseconds.

In the following two charts we see that the different messages are very similar except for minor variations.