Pulsin problem?

[dhouston]

How square are the pulses?

[Acetronics2]

Hi,

here, you are supposing your ECU Outputs a perfectly square wave ... is it real ???

At 1000 rpm or 16.667Hz, my LCD screen shows 950-1050 (hightime is around 1500counts)

??? 1500 counts are 3 ms @ 20 Mhz ... 6ms ( square wave ) per rev is ... 10 000 rpm !!! ... not 1000.

you have a calculation error somewhere !!!

let's say 15000 counts ...

60 000 000 / 2 / 2 / 15000 = 1000

60 000 000 is 60 Million µs in a minute
2 is for square wave ( you measure half duration )
2 is for 2 pulses per rev ( matches your DVM result ... hé,hé )
15000 is Pulsin result.

also see DIV32 for 60 E6 ( or 15 E6 ! ) value use ...


You'd better use " interrupts on edge " that would measure the full cycle ( High + Low parts of the signal ) regardless of the duty factor of your pulse ...

see " DT Instant interrupts " for that ... works great ++ aboard my Honda lawn tractor ( lol )

Alain

[Skylar]

Yeah, I have no idea how the pulses look nor do I have equipment to see it.

Acetronics, you are right about the hightime, it is 15000, I forgot I was looking at the number divided by ten on screen.

I'll try using interrupts, it will work that way but it'll take me a while to get my head around it.

Thanks.