adc => LPF lp => LPF lp2 => ZeroX z => FullRect f => OnePole p => blackhole; // basic patch
0.0 => float myZeroes;          // This holds the last zero crossing count
400.0 => lp.freq => lp2.freq; // this helps us to ignore harmonics
2.0 => lp.Q => lp2.Q;         // and noise, and higher fundamentals
    
spork ~ ZC(0.500);  
        
while (1)       {
    100.0 :: second => now;  // do other stuff here 
}
     
fun void ZC(float howoften)     {
    howoften*44100 - 1 => float wait;
    while (1)   {
        wait :: samp => now;
        p.last() => myZeroes;
    <<< "Zero Crossings = ", myZeroes >>>;
        0.0 => p.a1;
        0.0 => p.b0;
        1 :: samp => now;
        -1.0 => p.a1;   // this is dangerous, but we
        1.0 => p.b0;    // know what we're doing
    }
}