MAF output signal

[Stuart Baly]

>From: mjos at tsc.hh.avnet.com (mjos)

>I am working on a frequency limiting circuit that will intercept the 
output
>of my MAF sensor and pass the original freq as long as it falls at or 
>below a set limit.  If it goes above the limit freq, the circuit will pass 
only
>the limit freq. regardless of how high the input freq. goes beyond it.

>Has anyone else made such a circuit?  I am open to various ideas.

        Here's my two cents worth:

        Use a 4046 PLL as a F/V converter, then use a zener or similar to 
limit the voltage output. Then use the VCO from another 4046 to convert 
back to a frequency output.
        If you use well-matched components on both 4046's, the input and 
output frequencies should agree fairly well, until the input frequency 
rises above the point where the zener conducts, then the output will stay 
constant for all input frequencies above that.
        There might be other problems, for example 4046's can't output 0Hz 
without some changes to the surrounding circuitry, but this would have to 
be cheaper than a bought unit.
        I haven't built this, so there's a fair chance I'm talking rubbish.

Stuart

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             Stuart Baly (S.Baly at BoM.gov.au)
'71 Datrat 1600, '89 Kawasaki GPz900R, '81 Yamaha RD350LC
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