inductive vs optical

[Jeff Hansen]

I have been following the "Re: inductive vs optical" thread and quadrature keeps coming up. 
The _primary_ purpose for quadrature is to determine the direction of rotation. I'm pretty 
sure :-) that this is not important in this application. The _secondary_ purpose is to 
allow for a 4x multiplication of encoder resolution by using both edges of both sensors, 
this could be useful. I use encoders on just about every servo motor in every product that 
I have designed at work. I would not expect the 1000 line and 2500 line encoders that I 
use, to live very long under my hood. A 360 line encoder with an index pulse would be nice, 
but the only real improvement you will probably see would be simpler software. Don't you 
guys like software? 

[snip]
> This brings up an interesting point... Hewlett Packard makes a chip 
> specifically for reading optical encoders, which may work great with this 
> type of system.  Assuming you can get the 50% duty cycle waveforms as 
> mentioned above, (you could have some sort of sensitivity adjustment on
> the sensors so it picks up the tooth halfway up and down each ramp) the
> chip takes care of the *** QUADRATURE *** decoding and has a built in 16 bit counter

[snip]
> All you really need is the 2 *** QUADRATURE *** tracks, plus a single "index" marker
> which generates a pulse once per revolution.  In this manner, you have a sync
> pulse which tells you when you have gone one full turn, and simply reference
> everything to the sync pulse...

[snip]
> If you use two sensors for angle (eg *** QUADRATURE *** encoding), you can test for
> either of these failing as well. Ok, so if the engine rocks backwards when
> you switch it off will confuse this, but you don't care at this point.
> I'd prefer to have the sensor checking than to know how far my engine rocks
> back :-)
Andrew , I know you understand.

[snip]
> Why? As long as your timing resolution is high enough, and you don't rely
> on the micro for doing the *** QUADRATURE *** or handling a zillion interrupts,
> a micro should be able to handle up to 7 or 8000 RPM easily.  8000 RPM is 
> only about 1Khz.

Later -

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jeff Hansen
Anaheim, California, USA
JHansen777 at gnn.com
http://members.gnn.com/JHansen777/car/index.htm
Seven pounds of boost is a 'Good-Thing'
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