need help for measuring two freq at same time

Hi,

I am hobbyst, I want to measure two frequencies between 10hz to 500hz at same time on two different pins, ie measure two frequencies within same time base of 1000 mili sec . I tried "Count" but I cold not measure two inputs within same 1000ms. Is there a better way to do it?, any example code would help me lot.

I am using 16f73 @4mhz. Actually I am trying to measures pulses coming from my motor bikes spark plug, I have condtioned and converted pules picked up from spark plug and converted to TTL level. Other frequency input is coming from speed sensor.

These Pulses from spark plug are erratic, Does anybody have any circuit for getting reliable reading using PIC?.

Thanks in advance

regards
mahesh
VU2IIA

you could try using the "change on portb" interrupt. put both of the inputs on port b and then any change will trigger the interrupt. You could set up the interrupt handler to figure out which one has changed and using a timer and a bit of maths, work out both frequencies.

This is like super-crude... but it'll kinda work as a starting point...

Code:

---

        InputA var PortB.0
        InputB var PortB.1
        LED var PortB.4

        Temp var Byte
        ToggleA var Temp.0
        ToggleB var Temp.1

        CounterA var WORD
        InputACount var WORD
        InputBCount var WORD

        TRISB=%00001111       

Start:
        '
        '        Get Ready
        '        ---------
        ToggleA=0
        ToggleB=0
        InputACount=0
        InputBCount=0
        High LED                ' We're Ready...
        '
        '        Start Count
        '        -----------       
        For CounterA=0 to 3999
                If (InputA=0 and ToggleA=0) then ToggleA=1
                If (InputA=1 and ToggleA=1) then
                        InputACount=InputACount+1
                        ToggleA=0
                        endif
                If (InputB=0 and ToggleB=0) then ToggleB=1
                If (InputB=1 and ToggleB=1) then
                        InputBCount=InputBCount+1
                        ToggleB=0
                        endif
                PauseUS 250
                Next CounterA
        '
        '        Stop Count
        '        ----------
        Low LED
        LCDOut $FE,1,"A=",#InputACount,"Hz"
        LCDOut $FE,$C0,"B=",#InputBCount,"Hz"
        Goto Start                ' Loop forever

---

Yes, of course there are limitations... you'll have to trim PauseUS so that the For/Next Loop is exactly 1 second long... so put a scope on the LED pin... another limitation is that your Pulse must be wider than about 270uS so you may need some external circuitry... another is that probably 3.5kHz is a practical maximum count... but go play...

Hi Melanie & kamikaze47,

First of all New year Greetings to you. Thanks for replying and giving me helping hand.

Actually 2 Months back I purchased Cheap 100cc new motorcycle, which doesnt have RPM meter, so I wanted to make RPM meter and Speedometer for my bike. I am getting RPM signals from Spark plug and and Speedometer signal from hall sensor, which is just few hundred hz per seconds, but problem was how to measure both signals at same time.

Melanie, I will try your code, I will try not to bother you and use my small brain to its max.

Thank you once again,

regards
Mahesh-VU2IIA
my hobby page, if you have time to see.
http://www.vu2iia.bravehost.com/