IS501 sensor -- my solution

Tony Duell ard at p850ug1.demon.co.uk
Mon Oct 4 15:42:30 CDT 2010


> Hi Tony
>  Your solution to the waveform is interesting. You added the capacitor
> to fix the problem caused by the 74LS14. The problem is that the
> hysteresis of the LS14 is so large that it eats up the phase
> margines of the roughly sine/cosine from the optical sensors.

I don't think this is the same problem. Without the capacitors, and with 
the 470R resistors, I was getting waveforms with roughtly 1:1 mark-space 
ratio, and while not exactly in quadrature, pretty darn close. The only 
problem was that every so often (perhaps 1 in every 10000 pulses), there 
would be a glitch in one of the waveforms. It's not supply relateded, and 
I couldn't repodcude it by, say, jiggling the encoder disk.

But that glitch was taken by the elctronics as a valid pulse which upset 
things. 

AAdding the capacitors hasn't noticeably changed the mark:space ratio or 
the phasing. But it's got rid of the glitches. 

A lot of optical mice use the '14 and the output signals look pretty good 
to me. 

-tony




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