Posted on August 16, 2014 at 13:49Hi, I am trying to measure the rpm of a geared DC motor. The manufacturer claims a speed of 500rpm at 12V but my calculations give a speed of around 1600rpm! The gear ratio is 19:1.
I have written the following code to measure the speed:
//Systick setup for 1ms
void Delay(__IO uint32_t nTime)
{
TimingDelay = nTime;
while(TimingDelay != 0);
}
void TimingDelay_Decrement(void)
{
if (TimingDelay != 0x00)
{
TimingDelay--;
}
}
void SysTick_Init(void){
while (SysTick_Config(SystemCoreClock / 1000) != 0) {
}
}
void SysTick_Handler(void){
TimingDelay_Decrement();
}
//Initializing Timers for encoder interface
void InitENTim(void){
RCC_APB1PeriphClockCmd (RCC_APB1Periph_TIM4, ENABLE);
RCC_APB1PeriphClockCmd (RCC_APB1Periph_TIM2, ENABLE);
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_Period = 0xFFFF;
TIM_TimeBaseStructure.TIM_ClockDivision=0;
TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);
TIM_EncoderInterfaceConfig(TIM4, TIM_EncoderMode_TI12,TIM_ICPolarity_Rising, TIM_ICPolarity_Rising);
TIM_EncoderInterfaceConfig(TIM2, TIM_EncoderMode_TI12,TIM_ICPolarity_Rising, TIM_ICPolarity_Rising);
TIM_Cmd(TIM4,ENABLE);
TIM_Cmd(TIM2,ENABLE);
encodersReset(); //function to reset counter values
}
//The function to read the encoder and get Count
void encoderRead(void){
oldrightEncoder = TIM_GetCounter(TIM4);
Delay(10); //This should be a 10ms delay (according to my Systick config as written above)
rightEncoder = TIM_GetCounter(TIM4);
rightCount = rightEncoder - oldrightEncoder; //I am getting the difference in counts after 10ms
totalrightCount += rightCount;
oldleftEncoder = TIM_GetCounter(TIM4); //Encoder;
Delay(10);
leftEncoder = TIM_GetCounter(TIM4);
leftCount = leftEncoder - oldleftEncoder;
totalleftCount += leftCount;
}
//function to calculate speeds
void encoderCalculate(void){
volatile float a,b,x,y,z; //just some variables for ensuring I didnt make a mistake in simple maths
x = rightCount/64; //my encoder gives 64 counts per revolution when detecting both edges of both channels.
y = 1/x;
z = y*0.01; //This 0.01 is for the 10ms delay that I had for getting the difference in Count
a = 60/z;
b = a/19; //accounting for the gear ratio (19:1)
rightspeed = b;
x = leftCount/64;
y = 1/x;
z = y*0.01;
a = 60/z;
b = a/19;
leftspeed = b;
}
Is there any chance there is some sort of conflict in timing of the encoder timer and the systick timer? Obviously, there is some sort of a timing problem. Kindly help as I have been stuck on this problem for a quiet a long while.
#stm32 #tim #encoder
