Calculating a pulse period ?

[antonius]

Dear Members,

How can I count a pulse from a sensor with timer ?

How can I calculate the period of this pulse ?

samplebuff[i].ired   = buffer_rx[ j ];

       samplebuff[i].ired  <<=  8U;

       samplebuff[i].ired  |=  buffer_rx[ j + 1 ];

between

samplebuff[i].ired   = buffer_rx[ j ];

and another

samplebuff[i].ired   = buffer_rx[ j ];

?

Thanks

[S.Ma]

Get a TIMer example from a STM32 Cube Nucleo board project.

It's called Timer Input Capture for the generic way of doing it.

Connect the pulse source to the timer channel 1 for example.

Setup input capture on falling edge

The timer for example runs at 1MHz, count up to 65536 and overflows back to 0 forever.

If you use interrupt on falling edge of the input capture, save the value and substract it from the previous occuring interrupt.

Capture n=5 : read 0x0500

Capture n=6 : read 0x0680

Capture n=7 : read 0x800

Period is 0x680-0x500 = 0x180

Or 0x800 - 0x680 = 0x180

Works even with overflow... nothing to worry.

0x180 = 384 = 384 usec (1MHz timer) = 2.6 kHz

Lowest HW measureable frequency it the timer period.

Measuring the hgih and low time is possible, just select rise/fall edge for high level.

[Tesla DeLorean]

Configure TIM in External Count mode?

Configure the TIM in free-count mode, and time-stamp events, delta the CCRx samples.

[antonius]

I'm thinking with Hal_GetSystick ?

[antonius]

I got output like this :

Period After RED data= 129435 
                                                
Samples recorded 6
                                                            
LowPassFilterIR max 161.856598 
                                               
Data 6 Output MAX30100,0x09 register (FIFO DATA) IR : 694 
                    
DC filterIR = 660.994995
                                                      
MeanDiff filterIR = 660.000000
                                                
LowPass filterIR = 161.856598
                                                 
 
                                                                               
Period After IRRED data= 129643 
                                              
Data 6 Output MAX30100,0x09 register (FIFO DATA) RED : 694 
                   
DC filterRed = 660.994995
                                                     
MeanDiff filterRed = 660.000000
                                               
LowPass filterRed = 161.856598
                                                
 
                                                                               
Period After RED data= 129643 
                                                
Samples recorded 7
                                                            
LowPassFilterIR max 161.856598 
                                               
Data 7 Output MAX30100,0x09 register (FIFO DATA) IR : 696 
                    
DC filterIR = 662.950317
                                                      
MeanDiff filterIR = 660.000000
                                                
LowPass filterIR = 161.856598
                                                 
 
                                                                               
Period After IRRED data= 129837 
                                              
Data 7 Output MAX30100,0x09 register (FIFO DATA) RED : 696 
                   
DC filterRed = 662.950317
                                                     
MeanDiff filterRed = 660.000000
                                               
LowPass filterRed = 161.856598
                                                
 
                                                                               
Period After RED data= 129837 
                                                
Samples recorded 8
                                                            
LowPassFilterIR max 161.856598 
                                               
Data 8 Output MAX30100,0x09 register (FIFO DATA) IR : 694 
                    
DC filterIR = 660.852417
                                                      
MeanDiff filterIR = 660.000000
                                                
LowPass filterIR = 161.856598
                                                 
 
                                                                               
Period After IRRED data= 130032 
                                              
Data 8 Output MAX30100,0x09 register (FIFO DATA) RED : 694 
                   
DC filterRed = 660.852417
                                                     
MeanDiff filterRed = 660.000000
                                               
LowPass filterRed = 161.856598
                                                
 
                                                                               
Period After RED data= 130032 
                                                
Samples recorded 9
                                                            
LowPassFilterIR max 161.856598 
                                               
Data 9 Output MAX30100,0x09 register (FIFO DATA) IR : 34835 
                  
DC filterIR = 34801.957031
                                                    
MeanDiff filterIR = 660.000000
                                                
LowPass filterIR = 161.856598
                                                 
 
                                                                               
Period After IRRED data= 130239 
                                              
Data 9 Output MAX30100,0x09 register (FIFO DATA) RED : 34835 
                 
DC filterRed = 34801.957031
                                                   
MeanDiff filterRed = 660.000000
                                               
LowPass filterRed = 161.856598
                                                
 
                                                                               
Period After RED data= 130239 
                                                
Samples recorded 10
                                                           
LowPassFilterIR max 161.856598 
       

How can I take the maximum output as my starting period (1) and end period (2) ?

I have LowPassFilterIR max and LowPassFilterRed max values ...

Thanks

[antonius]

I have

        max = 0;
      
      if ( lowPassFilterIR>max)
			{
                                 max =  lowPassFilterIR;
				printf("LowPassFilterIR max %f \r\n",lowPassFilterIR);
			}
		  
		

How can I take timestamp of that value ?

[Tesla DeLorean]

Keep track of when you take each sample, or understand the sample rate.​

[antonius]

probably ascending bubble sort can help me ?

[antonius]

https://en.wikiversity.org/wiki/C_Source_Code/Sorting_array_in_ascending_and_descending_order

[antonius]

How can I connect the timer input ? the output of the sensor is in the code ?