In article ,
"Michael A. Terrell" wrote:

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.


Diodes across the limit switch, so it can only run the other
direction. This was common on Sat dish steering motors, and trailer
jacks. You hit the limit, and the switch opens, but the diode will allow
it to be backed off.

That would certainly work for a DC motor. Multiwinding AC motors are a
bit different, but it can be done.

I wasn't intending to design it sight unseen, but wanted to ensure that
the issue was addressed. And that software was properly distrusted.

Joe Gwinn



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