Joseph Gwinn wrote:
In article ,
cavelamb wrote:

[snip]
I would like to see limit switches at each end just for safety sake.
That would take up two bits of input per vent.
But if the device has comfortable "over-run" areas, it might not be needed.

I agree that limit switches are needed, but they should physically
interrupt power to the motor, and in no way depend on software.

The problem is that once these limits are hit, the computer can no
longer recover control, and a manual reset is needed.

The usual solution is to have two sets of limit switches, inner and
outer.

The inner limit switches are sensed by the computer, telling it to stop
moving in that direction.

The outer set physically interrupts power to the motor, to prevent
damage should the computer fail to do the right thing.

Joe Gwinn


There is an old saying that,
"If engineers built bridges the way programmers write software,
the first wood pecker than comes along could destroy civilization".

And there is some truth in that.

But no, I'd not design an autonomous system that need manual oversight.

IIRC, Karl said his vent was about 6 feet long.

My first fantasy was a fabric tape/shade (wide enough to cover the vent slot)
that rolls up on rollers at each end. Maybe it has some shaped supports
to keep it snug against the enclosure(?). But there is nothing to jam into
at the end of the run.

So all I'd be doing is rolling the shade up or down.

The computer can monitor the drum and tell, within reason, where the opening
is at any time. If we are rolling up on a fairly small shaft, just count
turns. If it's a big drum, maybe glue some magnets around the drum and count
them with a Hall effect sensor.

You don't see that kind of proactive defense in other mechanical devices.
Printers, Plotters, Flight simulator motion platforms, CARS.

But you do have to be careful about writing any wood peckers into your code.


Richard