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Re: Solving the need for ISA or USB slots and Serial Ports

On Wed, 02 Jul 2003 14:16:51 -0500
"Bruce Bostwick" <lihan161051@earthlink.net> wrote:
> Although, you're right, either the node will need to be smart enough to 
> be able to prevent damage if the start command goes through and the 
> stop command doesn't.  Although, what I was thinking of for rotators 
> was more of a servo loop control, where the computer would send out a 
> specific "setpoint" value, fed to the rotor servo as voltage, current 
> loop, what have you, and the rotor would automatically track that 
> setpoint and not need separate "start" and "stop" commands, just a 
> single write and latch operation into a DAC.
> I know most rotators today don't do it that way, but I've been thinking 
> for years that it's time they did .. simpler control and less chance of 
> runaway operation.  It's simple enough to do nowadays .. three wire 
> interface with DC power, ground, and setpoint voltage .. and you can 
> even limit the input voltage with simple op amp circuits so if a short 
> somewhere drives the input to one rail or the other the rotator will 
> still not end up grunting against the stop.
> Yeah, I know, I'm being an armchair engineer, but it's worth thinking 
> about, since basically it's a gear reduction DC motor, a position 
> sensing pot, and some op amp circuitry with maybe a few MOSFET driver 
> bridges added in.  Definitely feasible in this day and age, and would 
> integrate very nicely with a LAN-based station control system ..

I've noticed that FOD track does something like that.  The problem I see with that is what happens if the rototor stops moving for some reason (trees, cables, ...).

Either one of these single board computers or a pic could do some checking to if the sense voltage hasn't changed in the last few seconds and if so stop the rotator.  And have a longer timeout for the command in case the rotator is moving but not well.

But I agree, having the controller handle this so if something happens on the network or the computer hangs the rotator doesn't try to keep moving.

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