Description
Today in this tutorial I am going to interface IR Remote with STM32 microcontroller. IR Remote Controllers and receivers follow some standard protocols for sending and receiving data. Some of these protocols are NEC , JVC , SIRC etc. Here we will be discussing only the NEC protocol. I will also use LCD16x2 to display the key pressed on the remote. But first let’s see what NEC protocol is.
NEC Protocol
In NEC Protocol, a logic 0 is indicated by 562.5µs pulse burst followed by a 562.5µs space, with a total transmit time of 1.125ms and a logic 1 by 562.5µs pulse burst followed by a 1.6875ms space, with a total transmit time of 2.25ms.
Whenever a key is pressed, the following is transmitted:-
1. A 9 ms leading pulse
2. A 4.5 ms space
3. The 8-bit address
4. The 8-bit logical inverse of the address
5. The 8-bit command
6. The 8-bit logical inverse of the command
7. Finally a 562.5µs pulse burst to show end of message transmission
How to Decode
Decoding any IR protocol is not difficult at all. The IR receiver is a photodiode and pre-amplifier that converts the IR light into an electrical signal. It converts the active HIGH signal to active LOW. Also the signal pulse are continuous as shown in the picture below
Ok so in order to decode first we have to wait for the input pin to go low. Once the pin is LOW, we will wait for the pin to go HIGH. This should take around 9ms.
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while (HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1)); // wait for the pin to go low while (!(HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))); // wait for the pin to go high.. 9ms LOW |
Again wait for the pin to go low, which should take around 4.5 ms. And this will conclude the Start of Frame.
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while (HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1)); // wait for the pin to go low |
Now we are going to read the 32 bits and store them in a variable. To read a bit, we are going to check the length of the SPACE followed by the 562.5µs. If this length is more than 1 ms, that means the bit is ‘1’. If the length is less than 1 ms the bit is ‘0’.
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for (int i=0; i<32; i++) { count=0; while (!(HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))); // wait for pin to go high.. this is 562.5us LOW while ((HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))) // count the space length while the pin is high { count++; DWT_Delay_us(100); } if (count > 12) // if the space is more than 1.2 ms { data |= (1UL << (31-i)); // write 1 } else data &= ~(1UL << (31-i)); // write 0 } |
Next we need to assign the values to the key pressed on the Remote. I will also print these characters on the LCD. Below is the code to do that.
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switch (code) { case (0xFFA25D): lcd_send_cmd (0x86); lcd_send_data ('1'); break; case (0xFF629D): lcd_send_cmd (0x86); lcd_send_data ('2'); break; case (0xFFE21D): lcd_send_cmd (0x86); lcd_send_data ('3'); break; case (0xFF22DD): lcd_send_cmd (0x86); lcd_send_data ('4'); break; case (0xFF02FD): lcd_send_cmd (0x86); lcd_send_data ('5'); break; case (0xFFC23D): lcd_send_cmd (0x86); lcd_send_data ('6'); break; case (0xFFE01F): lcd_send_cmd (0x86); lcd_send_data ('7'); break; case (0xFFA857): lcd_send_cmd (0x86); lcd_send_data ('8'); break; case (0xFF906F): lcd_send_cmd (0x86); lcd_send_data ('9'); break; case (0xFFB04F): lcd_send_cmd (0x86); lcd_send_data ('#'); break; case (0XFF6897): lcd_send_cmd (0x86); lcd_send_data ('*'); break; case (0xFF9867): lcd_send_cmd (0x86); lcd_send_data ('0'); break; case (0xFF38C7): lcd_send_cmd (0x86); lcd_send_data ('K'); break; case (0xFF18E7): lcd_send_cmd (0x86); lcd_send_data ('^'); break; case (0xFF10EF): lcd_send_cmd (0x86); lcd_send_data ('<'); break; case (0xFF5AA5): lcd_send_cmd (0x86); lcd_send_data ('>'); break; case (0xFF4AB5): lcd_send_cmd (0x86); lcd_send_data ('u'); break; default : break; } |
You can download the code below..
CODE
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/* Includes ------------------------------------------------------------------*/ #include "main.h" /* Private includes ----------------------------------------------------------*/ /* USER CODE BEGIN Includes */ #include "dwt_stm32_delay.h" #include "i2c-lcd.h" /* USER CODE END Includes */ uint32_t data; uint8_t count; uint32_t receive_data (void) { uint32_t code=0; /* The START Sequence begin here * there will be a pulse of 9ms LOW and * than 4.5 ms space (HIGH) */ while (!(HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))); // wait for the pin to go high.. 9ms LOW while ((HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))); // wait for the pin to go low.. 4.5ms HIGH /* START of FRAME ends here*/ /* DATA Reception * We are only going to check the SPACE after 562.5us pulse * if the space is 562.5us, the bit indicates '0' * if the space is around 1.6ms, the bit is '1' */ for (int i=0; i<32; i++) { count=0; while (!(HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))); // wait for pin to go high.. this is 562.5us LOW while ((HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1))) // count the space length while the pin is high { count++; DWT_Delay_us(100); } if (count > 12) // if the space is more than 1.2 ms { code |= (1UL << (31-i)); // write 1 } else code &= ~(1UL << (31-i)); // write 0 } return code; } int main(void) { /* USER CODE BEGIN 1 */ /* USER CODE END 1 */ /* MCU Configuration--------------------------------------------------------*/ /* Reset of all peripherals, Initializes the Flash interface and the Systick. */ HAL_Init(); /* USER CODE BEGIN Init */ /* USER CODE END Init */ /* Configure the system clock */ SystemClock_Config(); /* USER CODE BEGIN SysInit */ /* USER CODE END SysInit */ /* Initialize all configured peripherals */ MX_GPIO_Init(); MX_I2C1_Init(); /* USER CODE BEGIN 2 */ DWT_Delay_Init (); lcd_init (); /* USER CODE END 2 */ /* Infinite loop */ /* USER CODE BEGIN WHILE */ while (1) { /* USER CODE END WHILE */ /* USER CODE BEGIN 3 */ while (HAL_GPIO_ReadPin (GPIOA, GPIO_PIN_1)); // wait for the pin to go low data = receive_data (); convert_code (data); HAL_Delay (200); } /* USER CODE END 3 */ } |
Connection
Result
that was so helpful would you please send me(email) the papers you have used for this?