calculate time between pulses

[hell_pk]

Hi!
I want to know how to calculate exact time between two pulses.Input is a pulse train with variable frequency.just want to calculate time between rising or falling edge of one pulse and the second one then second one and third one continously.
thnx

[BrianT]

If the pulse train is slow, an all-Basic approach could be something like

Loop:
Counter = 0
input sensepin
if sensepin = 0 then Loop
TimeHigh:
counter = counter + 1
pauseus 1000
if sensepin = 1 then TimeHigh
TimeLow:
counter = counter + 1
pauseus 1000
if sensepin = 0 then TimeLow
Done:
Serout Tx232, 2, ["Pulsewidth = ", #counter, ", mSecs"]
GOTO Loop

This will need tweaking (by reducing the pauseus period) to get the timing exact. An oscilloscope needed.

If your target pulse rate is too fast for the above you will need to setup Timer1 or Timer3 then invoke the CCP register which will give you the number of ticks of Timer1/3 between events on the defined CCPx pin. This will give you microsecond speeds and very high accuracy which can be defined by analysis rather than measurement in the Basic approach above.

HTH
Brian

[hell_pk]

Ok here is a code for CCP but for some reason it is not working:
Define LCD_DREG PORTD ' Define LCD connections
Define LCD_DBIT 4
Define LCD_RSREG PORTD
Define LCD_RSBIT 2
Define LCD_EREG PORTD
Define LCD_EBIT 3



Lcdout $fe, $80, " Pulse Reader"

Pause 2000
Lcdout $fe, $1





Period var Word
Capture var PIR1.2
Overflow var PIR1.0 CCP1CON = %00000100
T1CON = %00000001
Loop:
While Capture = 0 : Wend

Period.lowbyte = CCPR1L Period.highbyte = CCPR1H
If Overflow = 0 Then Lcdout $fe, $80, "Input Period: " , #Period , "uS"
Endif
Capture = 0 ' Clear the capture flag
Rst:
While Capture = 0 : Wend
TMR1L = 0 TMR1H = 0
Capture = 0
Overflow = 0
Goto loop

[J. Mark Wolf]

I've used the PULSEIN command as a tachometer for years.

One trick is to employ a flip-flop in the signal chain that acts as a frequency divider. This has the effect of generating a single high pulse between two succesive edges, allowing the PULSEIN command to work, without having to switch context to time the high portion of the period and then the low portion of the period.

[Acetronics2]

Hi, Hell_pk

<< I want to know how to calculate exact time between two pulses. >>

The question 1 ) is : How exact must be your "exact time" ??? : +/- 1 ms ? +/- 1µS ... better accuracy ???

The Question 2) is : Which is the period ( approximate ... ) of your signal.

Could you also tell us what is your "signal" ???


Then we will be able to show you ideas ...

Alain

[hell_pk]

signal is ttl from spindle of an old CNC machine.i want to measure rpm.max rpm are 2400 so max frequency is 50 Hz.the code i wrote above is now working correctly to calculate period.now iwant to calculate rpm.
rmp=60/period
should do the trick i think
but how to perform this division?
accuracy is not a problem now.