How can I measure Duty cycle ?

[skimask]

Hello friends ,

I`m trying measure my cars injectors duty cycle .
Have any body experince about this ?

For example ,
injectors running pwm cycle ,
if injectors full open ,I must see %100 duty cycle on the display.

Im trying measure injectors cycle (ms) than calculate duty ,
but this is not correct way I think .

This kit ,
http://www.jaycar.com.au/productView...=&SUBCATID=347

working great ,They are use a 16F84 pic only .

thanks

PBP...
Use the Pulsin twice; once to measure the pulse width when low, then right after that, measure the pulse width when high. Add the two results together. Multiply the total result by 100 and divide that total by the pulse-high result and you'll get a percentage relating to a duty cycle. This will get you close, but not absolutely perfect. The total pulse width could change a lot between successive readings (i.e. during fast acceleration or deceleration) and completely ruin the end result. Maybe a little bit of software filtering or averaging over a couple of cycles added to the software.
JDG

[sayzer]

What about "Capture" ?


----------------------------------

[mister_e]

Yup that's the much accurate way if the PIC have the CCP module. Case not, Pulsin may work... but accuracy is pretty poor.

So you can still detect the rising edge, start a timer, wait 'till falling edge. You have now the High Pulse measure. From there you reset the Timer and wait the next rising edge. There you have the Low pulse measure.

Few maths later, you have the duty cycle.
http://www.picbasic.co.uk/forum/show...36&postcount=4

also look at this one
http://www.picbasic.co.uk/forum/show...se+measurement

HTH

[MaxiBoost]

Yup that's the much accurate way if the PIC have the CCP module. Case not, Pulsin may work... but accuracy is pretty poor.

So you can still detect the rising edge, start a timer, wait 'till falling edge. You have now the High Pulse measure. From there you reset the Timer and wait the next rising edge. There you have the Low pulse measure.

Few maths later, you have the duty cycle.
http://www.picbasic.co.uk/forum/show...36&postcount=4

also look at this one
http://www.picbasic.co.uk/forum/show...se+measurement

HTH

Hi again and thank your answers ,

Dear mister_e ,

I give to a circuit example in my first message (jaycar kit) use a 16F84A ,
This kit is working good and without any problem .
What is your comment ? or have you another idea ?
I think ,they must use very simple programme !
16F84 not have ccp module .

If you can help me ,thank you
if you can not ,thank you again

regards

[skimask]

Hi again and thank your answers ,
16F84 not have ccp module .

which is why I said to use the pulsin commands in the earlier post.

[MaxiBoost]

which is why I said to use the pulsin commands in the earlier post.

I can try but fail ,
Maybe Im not expert ,I dont .

[skimask]

I can try but fail ,
Maybe Im not expert ,I dont .

Ok, just to prove that the pulsin idea does work.........(within certain parameters anyways, I know it takes a finite amount of time for an injector to open and close and this amount would have to be accounted for in final calculations, and I also know that fuel rail pressure, system voltage, and injector/fuel temperature also have an effect on open/close times. I never said this method would be 100% accurate, but I'm sure the results can be tweaked thru software to get something fairly accurate.)

Do you have working hardware? In other words, do you have an input wire that could be or is connected directly to a PIC input pin? And if you connected an o'scope to that pin/wire, would the resultant signal on the 'scope follow/match the signal on the wire to the injector?

Without working hardware, further discussion would be fruitless...
So if you're just talking in theory, an idea you have...say so now so I (others?) don't use up too much time on this.

[ardhuru]

which is why I said to use the pulsin commands in the earlier post.

I'm afraid this does not work; after the first pulsin has taken its reading, since the transition has *already* happenned, the next pulsin of the opposite polarity (level?) will take place only at the next-to-next pulse. Of course, if the duty cycle for a sequence is going to stay somewhat the same then this should make no difference. I was trying to decode an IR signal by using these consecutive pulsins, and got completelty wrong results.

[sougata]

Hi,

I am not sure about the fuel injection stuff. Possibly a variable duty and variable frequency. One option may be to use the portb on change interrupt feature. So for every falling or rising edge you get an interrupt. One problem is that depending on the timer prescaler you may run out of time if the frequency is too low causing a timer overflow. Again that can be accounted with ISR checking for timer overflow and incrementing a pseudo timer high byte counter making the timer a 16bit one.