68HC11 and MAF sensor

[Denis Rouleau]

>
>Hello to all, I have a question I have a MAF sensor off an 2.8L firebird it
>puts out a pulse that varies
>from 30hz to 150hz that = 3 to 150 grams/sec air flow according to the GM
>efi training manual I have. I not 
>sure how to handle the conversion in the microcode I am using a HC11 micro
>and was hoping to find 
>someone who knows more about programing than I do . I am very much an
>amateur programer and any help
>would be great.  My second question why do they convert to freq, just using
>the 0 to 5 volts output
>would be easier wouldn't it.  
>
>                                   Jimmy
>
>staton at icon.net
>
>
>
Jimmy,
	first, you could measure the time between rising edges of the
signal and use a lookup table to handle the conversion. Since they are low
frequencies, you HC11 would not be spending too much time on this task.
Just feed the signal to an interrupt if one is available (or poll it at
regular intervals using a timer for your timebase). You could also use a
frequency to voltage converter and an Analog to Digital converter but that
adds cost and complexity and is not really needed at these frequencies. 

Second, the MAF sensor is operating in a VERY NOISY environment full of high
frequency noise. By using low frequencies, they can easily filter out the
high freq energy. They may have other reasons to do it as well. Anyone?

Salut 

Denis Rouleau
ca904 at freenet.carleton.ca

--
Salut.

Denis Rouleau  (ca904 at freenet.carleton.ca)