IR Communication Using Core Independent Peripherals: IR Receiver

Introduction

Many real-time control applications use infrared (commonly referred to as IR) wireless technology as a mode of communication. IR communication has the advantages of low-power consumption and reasonable cost. It is widely used in various control applications that involve the transmission of information and commands to operate different household appliances. Some commonly used home appliances that utilize IR communication include remote controls for televisions, air conditioners, and more. There are several standard IR protocols in use, such as S-link, RECS-80, RC-5, RC-6, and NEC. However, the most commonly used protocol is the NEC IR protocol.

To see the IR Communication transmitter and receiver demo operation video, click the below image.

Related Documentation

• PIC18F47Q10 Product Page
• PIC18F47Q10 Code Examples on GitHub
• IR Communication Using Core Independent peripherals: IR Transmitter— MPLAB® Discover link
• AN2933 — DC Motor Control With Touch Interface and IR Communication

Software Tools

• MPLAB® X IDE v6.25.0 or newer
• XC8 Compiler v3.00.0 or newer
• Microchip PIC18F-Q Series Device Support Pack v1.28.451 or newer
• Microchip Code Configurator v5.6.2 or newer
• CCP Driver v4.1.1
• CLC Driver v4.4.0
• MSSP Driver v7.0.3
• PWM Driver v4.2.12
• TMR1 Driver v5.2.0
• TMR2 Driver v5.1.1
• SPI Host Driver v1.2.1

Note: To run the demo, the installed tool versions should be the same as, or later than, the specified versions. This example has not been tested with earlier versions.

Hardware Used

• PIC18F47Q10 Curiosity Nano
• Curiosity Nano Base for Click boards
• IR click

Setup

IR Receiver

The IR receiver unit is implemented using existing evaluation boards: the Curiosity Nano Base for click boards and the IR Click board. The TSOP38338 IR receiver module on the IR Click board is used to detect received IR commands. Figure 1 shows how to implement the IR receiver.

Figure 1. IR Receiver

The output of the IR Click board^TM, which is the demodulated data, is connected to a microcontroller (MCU) port pin. Whenever the first falling edge is detected on this port pin, the Hardware Limit Timer (HLT) module (Timer2 in this case), configured in Monostable mode, starts automatically. The timer will overflow after a few milliseconds, as determined by the period configuration. Upon a timer overflow interrupt, it is confirmed whether the data line is still low, ensuring that the detected falling edge was not caused by electrical noise.

The Capture/Compare/PWM (CCP) peripheral is used to capture the timings of the incoming data frame. The CCP can be used with either port B or port C of the MCU, but the demodulated data from the IR Click board is connected to port pin RA1. Therefore, the Configurable Logic Cell (CLC) is used as a buffer or interconnecting element to internally connect port pin RA1 to port pin RC0. RC0 is then used as the input to the CCP.

After the first valid falling edge is detected, the CCP with falling edge interrupt is enabled, and Timer 2 is disabled. The CCP is used along with Timer1 to detect the start sequence. After start detection, the captured values for the next 32 bits are stored in a buffer. While receiving data, the transaction is aborted if at any time the captured value goes out of range, and the registers, variables, and peripherals are reinitialized for the next valid IR frame detection.

If all the bits and edges are received correctly, Timer 1 is stopped, the CCP is disabled, and Timer 2 is enabled for the next IR frame detection. The command is then decoded from the CCP capture buffer. The received data is checked for the correct receiver address, the inverse of the address, the 8-bit command, and its inverse. If the address and its inverse, as well as the command and its inverse, match, the command data is reversed, since the Least Significant bit (LSb) of the command byte is transmitted first according to the NEC IR transmission protocol. The corresponding control action is then taken for the received command.

Configuration Settings

• Insert the IR Click board into mikroBUS™ slot 2 of the Curiosity Nano Base for Click boards
• Insert the LCD mini Click board into mikroBUS™ slot 3 of the Curiosity Nano Base for click boards
• The MCU port pins used in the application are described in the table below

Sr.No	MCU Port Pin #	Signal Name	Signal Description	IN/OUT
1	RA1	IR_RX	IR received signal	IN
2	RC0	CCP1	Capture input	IN
3	RA2	LCD_CS2	LCD mini chip select 2	OUT
4	RD7	LCD_CS	LCD mini chip select	OUT
5	RD5	LCD_Reset	LCD mini reset	OUT
6	RD1	LCD_PWM	LCD mini PWM	OUT
7	RC2	PWM	CCP2 PWM	OUT
8	RC6	SCK	SPI SCK for LCD	OUT
9	RC5	SDI	SPI SDI for LCD	IN
10	RC4	SDO	SPI SDO for LCD	OUT
11	RE0	LED	LED on PIC18F47Q10 Curiosity Nano board	OUT

Notes:

1. RC0 is configured as the CCP capture input pin. This is because only PORT B or PORT C can be used as CCP input. The IR Click board can feed received data only to pin RA1, so RC0 is connected to RA1 internally using the CLC as an interconnecting element.
2. The CCP2 peripheral is configured as PWM, and PORT C can be used as the CCP2 output pin. RC2 is configured as the CCP PWM output pin. According to the LCD mini Click schematic, the PWM signal for LCD brightness control should be available on port pin RD1. Therefore, RC2 is connected to RD1 internally using the CLC as an interconnecting element.
3. The output of the PWM3 peripheral is available on the RA3 pin. To control the RE0 LED brightness using PWM3, short the RA3 pin to RE0.
4. After making the above hardware connections, power on the board using a Micro-USB cable. Build the demo firmware and load the generated hex file to the PIC18F47Q10 MCU.

Figure 2. Demo Setup IR Receiver

Microcontroller Peripheral Configuration

Peripherals	Configuration	Usage
Clock Control	Clock source: HFINTOSC HF Internal Clock: 32 MHz Clock Divider: 1 Active Clock Tuning Update: Enabled	System clock
CLC1	Enable CLC: Enabled Logic Cell Mode bits: 4-input AND	Provides programmable logic
CLC3	Enable CLC: Enabled Logic Cell Mode bits: 4-input AND Select CCP2_OUT as one of the inputs	Provides programmable logic
CCP1	CCP Mode: Capture Select Timer: Timer1 Input Signal: CCP1 pin Mode: Falling Edge CCP Interrupt Enable: Enabled	Used to time and control different events
CCP2	Enable CCP CCP Mode: PWM Select Timer: Timer4 Duty Cycle: 50%	Used to time and control different events
PWM	PWM Enable: Enabled Select a Timer: TMR4 PWM Polarity: active_lo	Used to generate Pulse-Width Modulation (PWM) signals
SPI	Clock Source: Fosc/4_SSPxADD Requested Speed (kHz): 100 Mode: Mode 0 Data Input Sample At: Middle	Used to transmit/receive data and communicate
TMR1	Clock Source: Fosc/4 Clock Prescaler: 1:2 Timer Count Editor Enable: Enabled Requested Period: 2 ms	Used for configuring time-out
TMR2	Timer Enable: Enabled Control Mode: Roll over pulse Clock Source: LFINTOSC Clock Frequency: 31 kHz Clock Prescaler: 1:1 Requested Period: 2 ms TMR Interrupt Enable: Enabled	Used for configuring time-out
TMR4	Timer Enable: Enabled Control Mode: Roll over pulse Clock Source: Fosc/4 Clock Frequency: 8 MHz Clock Prescaler: 1:64 Requested Period: 2 ms	Used for configuring time-out

Demo Operation

IR Transmitter

• Switch S1 is used to send IR commands to the IR receiver
• Pressing switch S1 will send an IR command equal to the switch press count plus 0x80 (i.e., from 0x81 to 0x88). After the eighth press, the commands from 0x81 to 0x88 are repeated.

IR Receiver

• After reset, the IR receiver will wait for a command to be received, and the message "Waiting for CMD" will be displayed on the LCD
• If any command is received from the IR transmitter board, the corresponding control action is taken, and the received command along with the control action is displayed on the LCD screen
• If there is any error during reception—such as an error in the start of the frame, an error in data bit length, a receiver address mismatch, or an error in the command byte—a corresponding error message will be displayed on the LCD, and the receiver will be ready for the next IR frame reception
• Press Switch S1 to Send Command #81 to the receiver, as shown in Figure 3

Figure 3. Press Switch S1 to Send Command #81

• Receiver after receiving command #81:

Figure 4. Receiver After Receiving Command #81

• Below is the list of all commands and control actions.

1. Command #81: make brightness of LED 25%.
2. Command #82: make brightness of LED 50%.
3. Command #83: make brightness of LED 75%.
4. Command #84: make brightness of LED 100%.
5. Command #85: make brightness of LED 75%.
6. Command #86: make brightness of LED 50%.
7. Command #87: make brightness of LED 25%.
8. Command #88: make brightness of LED 0%.

Conclusion

This demo example demonstrates the use of important features of PIC18-Q10 MCUs for simple real-time control applications. It provides an overview of IR communication using the NEC infrared transmission protocol. The IR transmitter is implemented using Core Independent Peripherals (CIPs) of the PIC18-Q10 microcontroller, such as CLC, PWM and and DSM peripherals, with minimal CPU intervention. The IR receiver is implemented using Timer2, CCP and Timer1 peripherals of the PIC18-Q10 microcontroller. The combination of PWM, CCP, CLCs, DSM, and other core independent peripherals, along with generic peripherals such as timers and HLTs available in PIC18-Q10 MCUs, offers lower system cost, low-power consumption, facilitating reliable, deterministic and safe application development. These microcontrollers can be used for a wide range of general-purpose, low-power, and reliable real-time control applications, such as remote control of various home appliances and remote-controlled toys for children.