Subject:
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RE: Ball-less mice (was :Re: FW: Another DIY sensor)
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 30 Nov 2000 19:08:42 GMT
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Original-From:
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John Barnes <barnes@*antispam*sensors.com>
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Viewed:
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832 times
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Chris wrote:
>The Lego rotation sensor supplies four different voltage values as it
>rotates so that you can tell in which direction it is rotating. I thought
>the ball-mice use disks with an optical sensor that senses lines on
>the disk. Using the optical disk how do you determine which direction
>the disk is rotating?
That is really quite straight forward. The A and B channel outputs from the
mouse rotation sensor are simply passed through the two comparators in
the LM393. The outputs from the two comparators are pulled up to +5 with
10k resistors and summed via a 15k and 6.8k resistor for input to the RCX.
These combinations of values create the four voltages which are within a few
milli-volts of the Lego sensors outputs, so I suspect it is how they do it
too,
although I haven't taken mine apart to check.
______ _____
___/ \______/ A channel
_ ______ ___
\_____/ \______/ B channel
^ ^ ^ ^
The A and B channel outputs summed together give the four different voltages
for each of the four possible phases as shown in the rather crude diagram.
This makes the output from the mouse sensor indistinguishable from the
genuine Lego one from the RCX's end of things, and so it happily counts
out the position.
JB
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