Re: Star Trek spinner jumps

"Christopher X. Candreva" wrote:
>
> Other than that, I'm stumped. The schematcs are less than helpfull. The
> cabinet wring diagram calls P21 pins 1/4 Clock and Direction, which I think
> is wrong. They should simply be two 90-degree out of phase wave forms, from
> which you can derive clock and direction, am I correct ?
>
> Then the output of the little interface board are just labeled B0 - B7 ,
> whch isn't very helpful. Is there an actual clk/dir signal I can check ?

They can be called clock and direction, even though that may not seem to
make sense.

Typically one line will connect to the clock pin of a flip-flop and the
other to the "D" input of the same flip-flop.

For a better explanation, connect both lines to a scope and trigger off
one input (in effect, trigger=clock). As you turn the knob in one
direction you will see the other output is always be low at the trigger
(clock) point. Turning it the other direction the other output will
always be high at the trigger point. In effect, then, one line is the
clock and the other gives you direction information.

See, it sorta makes sense, doesn't it?

Ideally the outputs are square waves with no in-between voltages. As
you have seen, though, it isn't always that way. Usually (if the
manufacturer really wants it to work right) the lines will go through
Schmidt trigger gates to square them up. If connected to regular logic
instead of Schmidt trigger logic the "in between" states can cause the
gate to oscillate. This isn't much of a problem for the "direction"
input since it will have stabilized by the time the "clock" comes
along. But if an oscillation is on the "clock" line it will cause
multiple counts when there should only be one.

U4 on the "rotary controller" board is the Schmidt trigger. It MUST be
a 74LS14. If someone has replaced it with a '04 it needs to be changed
back to a '14.

Hope that is at least some help.

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Received on Sat Feb 16 22:49:34 2002