Re: Stupid 4024 freq divider question (shaft encoder resolution)

From: petrus bitbyter (p.kralt_at_reducespamforchello.nl)
Date: 02/26/05 

Date: Sat, 26 Feb 2005 00:22:52 GMT

"Randy MacKenna" <randymackenna@yahoo.com> schreef in bericht
news:1109366781.527537.99080@f14g2000cwb.googlegroups.com...
> 1. Yes. 2. Yes.
>
> Actually, "I" don't want to try to set position and rotation of the
> motor -- I already have motor driver hardware and software that does
> this -- I just want to make the motor advance faster.
>
> Here's an example. The motor is currently at zero degrees. I want to
> move and stop the motor at 360 degrees - one full rotation. Today, I'd
> have to pulse the driver 4000 times to effect that amount of rotation
> (1000 CPR encoder, quadrature = 4000 pulses per revolution). Instead,
> I want to pulse the driver only 1000 times.
>
> Therefore, my thinking is that if I can "throw away" all but every 4th
> returned pulse out of both the A and the B channel, then the driving
> hardware (the stuff with the real 'brains') will only have to be pulsed
> 1000 times to effect one full rotation. I will tell the driver that it
> is connected to a 250 CPR encoder (I set this via software), thus when
> it sees every fourth returned pulse from the A and B channel, it will
> say "Ahh, my motor was just advanced by 1.44 degrees", an it will do
> the math the correct way and "land" the motor at the right spot.
>
> One other way to do this is to replace the optical disk in the encoder
> with a different disk of lower resolution. That, in effect, is a
> 'mechanical' way of dividing the A and B outputs by 4. I can't buy a
> replacement disk for this encoder...thus my desire to solve this
> digitally.
>
> I found this, which I could go out and buy (I'd need 4 of them). I'd
> like to avoid that cost, and at the same time solve this puzzle for my
> own education.
>
> http://www.usdigital.com/products/edivide/index.shtml
>
> I guess that this thing could be complex enough to contain a state
> machine and be doing the analysis of both A and B at the same time, and
> synthesizing new A and B outputs, based on the division factor
> specified by the DIP switches.
>
> If you think that is indeed the case, then I am in way over my head,
> and I just have to spring for the $160 to buy four of these units for
> my four motors...
>
> -Randy
>

Randy,

Assuming you have nice digital input signals, lets call them A en B, and you
want to make new ones, lets call them X and Y, you can try the following
quick and dirty circuit:

A four bits positive edge triggered up/down counter is the heart of the
circuit. Connect A to the clock input and B to the up/down input. The ripple
output of the counter can be used to toggle a flipflop giving you the X
signal.

The Y signal is the problem. You need to decode 0011 of the counter(two
inverters and an AND.) This signal has to clock a D-type flipflop with B XOR
X on its data-input, giving the Y on the output.

petrus bitbyter

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