![\"\"](\"https:\/\/blog.embeddedexpert.io\/wp-content\/uploads\/2022\/05\/What-Does-RPM-Mean-in-Carss-1024x483.jpg\")
<\/figure><\/div>\n\n\n\n<\/p>\n\n\n\n
In the previous guide (here<\/a>), we saw how to configure timer to work in encoder mode. In this guide, we shall take it step further and measure the rotational speed in RPM (Revolutions per Minutes).<\/p>\n\n\n\n <\/p>\n\n\n\n In this guide, we shall cover the following:<\/p>\n\n\n\n <\/p>\n\n\n\n <\/p>\n\n\n\n <\/p>\n\n\n\n Since the encoder is used to measure the RPM, the timer will overflow at each full rotation. Hence we can use interrupt to measure the timer between each full rotation in milliseconds.<\/p>\n\n\n\n Since the timer will count up to the number of PPR provided by the encoder, an interrupt is generated. When the interrupt is generated, the time difference in milliseconds between each interrupt is measured and the the rptational speed in RPM is determined as following:<\/p>\n\n\n\n <\/p>\n\n\n\n First, measure the time difference in seconds as following:<\/p>\n\n\n\n Then determine the frequency in Hz as following:<\/p>\n\n\n\n Then determine the RPM by multiplying the frequency by 60:<\/p>\n\n\n\n In order to test the code, a crude is conducted which includes the following components:<\/p>\n\n\n\n <\/p>\n\n\n\n <\/p>\n\n\n\n <\/p>\n\n\n\n Since the timer in encoder is already discussed, we shall implement it here differently, we shall use timer3 and pins PB4 and PB5 as inputs for the timer<\/p>\n\n\n\n Hence the initializing the encoder mode as following:<\/p>\n\n\n\n The interrupt handler as following:<\/p>\n\n\n\n For measuring RPM function:<\/p>\n\n\n\n If the time difference is zero, we shall return 0 indicating that the RPM is zero or beyond the capability of the current implantation.<\/p>\n\n\n\n <\/p>\n\n\n\n Global variable:<\/p>\n\n\n\n The header file:<\/p>\n\n\n\n <\/p>\n\n\n\n Since the code requires millis function, systick timer is used to generate interrupt each 1 milliseconds and delay as well as the following:<\/p>\n\n\n\n The header:<\/p>\n\n\n\n For the lcd screen, i2c based one is used and you can get the code from here<\/a>.<\/p>\n\n\n\n For the stepper motor, please refer to the following<\/a> topic.<\/p>\n\n\n\n You may download the code from here:<\/p>\n\n\n\n1. How to Measure RPM:<\/h2>\n\n\n\n
![\"\"](\"https:\/\/blog.embeddedexpert.io\/wp-content\/uploads\/2022\/05\/Screen-Shot-2022-05-31-at-9.51.14-AM-1024x626.png\")
<\/figure><\/div>\n\n\n\n![\"\"](\"https:\/\/blog.embeddedexpert.io\/wp-content\/uploads\/2022\/05\/Screen-Shot-2022-05-31-at-10.18.08-AM.png\")
<\/figure><\/div>\n\n\n\n![\"\"](\"https:\/\/blog.embeddedexpert.io\/wp-content\/uploads\/2022\/05\/Screen-Shot-2022-05-31-at-10.19.53-AM.png\")
<\/figure><\/div>\n\n\n\n![\"\"](\"https:\/\/blog.embeddedexpert.io\/wp-content\/uploads\/2022\/05\/Screen-Shot-2022-05-31-at-10.20.54-AM.png\")
<\/figure><\/div>\n\n\n\n2. Proposed Experiment:<\/h2>\n\n\n\n
![\"\"](\"https:\/\/blog.embeddedexpert.io\/wp-content\/uploads\/2022\/05\/Screen-Shot-2022-05-31-at-11.47.42-AM.png\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/blog.embeddedexpert.io\/wp-content\/uploads\/2022\/05\/IMG_8488-1024x768.jpg\")
<\/figure><\/div>\n\n\n\n3. Firmware development:<\/h2>\n\n\n\n
void Encoder_init(uint16_t max_count)\n\t{\n\tRCC->APB1ENR|=RCC_APB1ENR_TIM3EN;\n\tRCC->AHB1ENR|=RCC_AHB1ENR_GPIOBEN;\n\n\t\/*GPIO B configuration for timer mode *\/\n\tGPIOB->MODER|=GPIO_MODER_MODE4_1|GPIO_MODER_MODE5_1;\n\tGPIOB->MODER&=~(GPIO_MODER_MODE4_0|GPIO_MODER_MODE5_0);\n\tGPIOB->AFR[0]|=(AF02<<16)|(AF02<<20);\n\n\t\/*Timer configuration for encoder mode *\/\n\tTIM3->ARR = max_count; \/\/set the max count\n\t\/*Timer in encoder mode*\/\n\tTIM3->CCMR1 |= (TIM_CCMR1_CC1S_0 | TIM_CCMR1_CC2S_0 );\n\tTIM3->CCER &= ~(TIM_CCER_CC1P | TIM_CCER_CC2P);\n\tTIM3->SMCR |= TIM_SMCR_SMS_0 | TIM_SMCR_SMS_1;\n\t\/*Enable interrupt*\/\n\tTIM3->DIER|=TIM_DIER_UIE;\n\tNVIC_EnableIRQ(TIM3_IRQn);\n\t\/*Start the timer *\/\n\tTIM3->CR1|=TIM_CR1_CEN;\n\n\t}\n<\/pre><\/div>\n\n\n\nvoid TIM3_IRQHandler(void)\n\t{\n\n\tif(TIM_SR_UIF&&TIM3->SR)\n\t\t{\n\t\tif(dir==1)\n\t\t\t{\n\t\t\ttime=millis()-first;\n\t\t\tdir=0;\n\t\t\t}\n\t\telse {\n\t\t\tfirst =millis();\n\t\t\tdir=1;\n\t\t\t}\n\n\t\tTIM3->SR&=~TIM_SR_UIF;\n\t\t}\n\t}\n<\/pre><\/div>\n\n\n\nfloat get_rpm()\n\t{\n\ttime=(time\/1000); \/*from microseconds to seconds*\/\n\tif(0==time)return 0;\n\tfrequency=1\/time;\n\treturn frequency*60;\n\t}<\/pre><\/div>\n\n\n\n#include "stm32f4xx.h"\n#include "stdint.h"\n#include "RPM_Encoder.h"\n#include "delay.h"\nconst int AF02=0x02;\nvolatile uint64_t first, second, dir;\nfloat frequency;\nfloat time;<\/pre><\/div>\n\n\n\n
\n#ifndef RPM_ENCODER_H_\n#define RPM_ENCODER_H_\n\nvoid Encoder_init(uint16_t max_count);\nfloat get_rpm();\n<\/pre><\/div>\n\n\n\n
#include "delay.h"\n#include "stm32f4xx.h" \/\/ Device header\n\n\nvolatile uint64_t ms,rms;\nvoid systick_init_ms(uint32_t freq)\n\t{\n\t__disable_irq();\n\tSysTick->LOAD=(freq\/1000)-1;\n\tSysTick->VAL=0;\n\tSysTick->CTRL=7; \/\/0b00000111;\n\tNVIC_SetPriority(SysTick_IRQn,7);\n\t__enable_irq();\t\n}\n\nuint64_t millis(void)\n\t{\n\t__disable_irq();\n\trms=ms; \/\/store current ms in rms\n\t__enable_irq();\n\treturn rms;\n\t}\n\nvoid SysTick_Handler(void){\nms++;\n}\n\nvoid delay(uint32_t delay)\n\t{\n\t\n\t\tuint64_t start=millis();\n\tdo\n\t\t{}while(millis()-start!=delay);\n\t}\n<\/pre><\/div>\n\n\n\n#ifndef __delay__H__\n#define __delay__H__\n\n\n#include <stdint.h>\nuint64_t millis(void);\nvoid systick_init_ms(uint32_t freq);\nvoid delay(uint32_t delay);\n#endif\n<\/pre><\/div>\n\n\n\n
4. Code:<\/h2>\n\n\n\n