Encoder

1. Introduction

Rotating encoder is a input device that provides information about the direction and amount of rotation of a shaft. It has minimum two outputs, A and B, which are 90 degrees out of phase. The encoder generates a pulse each time it is rotated by a certain amount. The direction of rotation can be determined by the order of the pulses on the A and B channels.

Hall Encoder

Magnetic Encoder
Yumo Encoder

Open Drain Rotary Encoder
Encoder Channel Waveform

Note

Above magnetic encoder does not need pull up resistors as it has built-in pull up resistors. But the open drain encoder needs pull up resistors. For 3V3 VDD, 4K7 pull up resistors are better. For 5V VDD, 10K pull up resistors are better.

2. CubeMX Configuration

  • Open CubeMX and generate basic code with:

    • microcontroller: stm32f407vgt6 or board: STM32F407VG-DISC1

    • project name: microsecond_tick

    • Toolchain/IDE: Makefile

  • Go to Pinout and Congiguration > Timers > TIM1. Select Encoder Mode for Combined Channels.

  • Under Parameter Settings > Encoder, change the Encoder Mode to Encoder Mode T1 and T2. It is better to keep AutoReload Register value to 65535.

  • Generate Code.

    Encoder Configuration

3. Code to Read Encoder Count

  • Navigate to Core > Src and open main.c.

  • Include header file.

    /* USER CODE BEGIN Includes */
#include <stdio.h>
/* USER CODE END Includes */

  • Overwrite definition of _write as:

    /* USER CODE BEGIN 0 */
int _write(int file, char *data, int len)
{
  for (int i = 0; i < len; ++i)
  {
    ITM_SendChar(data[i]);
  }
  return len;
}
/* USER CODE END 0 */

  • Add code to read encoder count.

    /* USER CODE BEGIN 2 */
HAL_TIM_Encoder_Start(&htim1, TIM_CHANNEL_ALL);
uint32_t encoder_count = 0;
/* USER CODE END 2 */

/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
  encoder_count = htim1.Instance->CNT; // CNT value ranges from 0 to ARR value
  // You also can use:
  // encoder_count = __HAL_TIM_GET_COUNTER(&htim1);

   printf("Count: %lu\n", encoder_count);

   HAL_Delay(100);
}
/* USER CODE END WHILE */

4. Observe Output

  • Connect encoder A and B channels to TIM1_CH1 pin and TIM1_CH2 pin respectively.

  • Open STM32CubeProgrammer and see count on SWV by rotating encoder. If you used USB, see on terminal or serial monitor.

Caution

STM32F407VG-DISC1 TIM1 gives problem in high speed encoder reading if cable length is long. It is better to use other timers for high speed encoder reading.

Assignment: Calculate RPM.