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From: Tim Wescott on 26 Apr 2010 14:08
Walter Banks wrote:
>
> princekcs wrote:
>
>> why is it necessary to clock on rising and falling edge when reading a
>> quadrature encoder?
>
> You can decode with one edge only. If you use both edges then
> the resolution of the system will double.

You can decode with one edge only if you don't mind if the decoding is
error prone and noise sensitive. There's just not complete information
to take in all the cases unless you pay attention to both the rising and
falling edges of both channels.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: Spehro Pefhany on 26 Apr 2010 14:19
On Mon, 26 Apr 2010 11:08:01 -0700, Tim Wescott <tim(a)seemywebsite.now>
wrote:

>Walter Banks wrote:
>>
>> princekcs wrote:
>>
>>> why is it necessary to clock on rising and falling edge when reading a
>>> quadrature encoder?
>>
>> You can decode with one edge only. If you use both edges then
>> the resolution of the system will double.
>
>You can decode with one edge only if you don't mind if the decoding is
>error prone and noise sensitive. There's just not complete information
>to take in all the cases unless you pay attention to both the rising and
>falling edges of both channels.

If you only care about speed and not direction, one edge on one
channel may be sufficient.

From: Tim Wescott on 26 Apr 2010 14:19
Spehro Pefhany wrote:
> On Mon, 26 Apr 2010 11:08:01 -0700, Tim Wescott <tim(a)seemywebsite.now>
> wrote:
>
>> Walter Banks wrote:
>>> princekcs wrote:
>>>
>>>> why is it necessary to clock on rising and falling edge when reading a
>>>> quadrature encoder?
>>> You can decode with one edge only. If you use both edges then
>>> the resolution of the system will double.
>> You can decode with one edge only if you don't mind if the decoding is
>> error prone and noise sensitive. There's just not complete information
>> to take in all the cases unless you pay attention to both the rising and
>> falling edges of both channels.
>
> If you only care about speed and not direction, one edge on one
> channel may be sufficient.

Yes, but* only if the encoder is known to be turning, and if it's a
technology (i.e. optical or magnetic) that doesn't bounce.

I've always been information starved, and have always used all the edges
available to me -- which doesn't mean that the next project that comes
down the pike won't work fine with a single edge on a single channel.

* I'm really not in a pissy mood today -- pedantic, maybe, but not pissy.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: Stef on 26 Apr 2010 15:58
In comp.arch.embedded,
Tim Wescott <tim(a)seemywebsite.now> wrote:
> princekcs wrote:
>> why is it necessary to clock on rising and falling edge when reading a
>> quadrature encoder?
>
> Homework?
>
> It isn't always necessary, but paying attention to all the edges gives
> you a more robust system.

But paying attention to all edges doesn't necessarely mean you have to
*clock* on the edges. ;-)

--
Stef (remove caps, dashes and .invalid from e-mail address to reply by mail)

Depart in pieces, i.e., split.
From: Tim Wescott on 26 Apr 2010 16:07
Stef wrote:
> In comp.arch.embedded,
> Tim Wescott <tim(a)seemywebsite.now> wrote:
>> princekcs wrote:
>>> why is it necessary to clock on rising and falling edge when reading a
>>> quadrature encoder?
>> Homework?
>>
>> It isn't always necessary, but paying attention to all the edges gives
>> you a more robust system.
>
> But paying attention to all edges doesn't necessarely mean you have to
> *clock* on the edges. ;-)
>
Correct, and it's why I worded what I said the way I did.

It's far easier to make a little state machine (in either hardware or
software) with a pair of binary states that runs at a sample rate
guaranteed to catch every valid edge than it is to make a bit of
hardware that actually derives it's clock edges from the edges of the
incoming signals.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
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