suggestions on reading a pulsing vehicle speed sensor?

[Acetronics2]

Hi,

The counting method will mainly depend on the input pulses frequency ...

COUNT need lots of ... counts and if pulses frequency is low ...

Response time is very slow ...

One must try to make a PERIOD measurement, then. and better calculate a mean value over some cycles ...

the thing I like to do is have a big counter and fill it with sum of period samples ... so the sampling time remains quasi constant.

few long samples if engine runs slow, many short ones if engine runs fast ...

I also use a switchable 1:10 divider ( a 4017 ! ) upon the RPM range ...

This way, I had realised a model plane RPM meter ranging from 43 to 32,000 rpm ... with more than .1% accuracy and an acceptable response time ...

The interrupt way is trickier, because of false triggering to avoid ... so, a very well designed input stage has to be used ...

But it's the fastest response ( for shift Lights, i.e. when max. engine accel. is looked for ...)

Alain

[mackrackit]

I figured the COUNT example would be the easiest to get started with.

As for the low or high frequency issue, have two or three sub routines.
If COUNT is X,Y,Z goto a routine with a different COUNT PERIOD.

That's my story...

[Bruce]

Are PULSIN and COUNT the only options for reading a pulsing vehicle speed sensor input?

Do you need to count the number of pulses in a given period, or measure the width of a pulse/pulses?

[Acetronics2]

Hi, Bruce

If it is a for a speedometer, the " basic info " is pulses per km or mile ...

now , knowing how many pulses per km ( generally written on the odo dial ...) , you easily can transform period to kph ...

the question then turns into ...

" what to read ??? " ... km or kph ???

looks kph or mph was the initial request ...

Alain