Homebrew PCBs

On Fri, 22 Sep 2006 22:18:22 +0200, bigjamma <bigjamma@...> wrote:

>
> For example, I have a need to route the output of my drives on the
> basis of a three-position switch: e.g. "Off | Mill | Lathe".
> When "Mill" is selected, one group of output terminals become "live",
> when "Lathe" is selected, a different group becomes live.
> I could almost handle this if all outputs were 5V TTL signals.
> Unfortunately, only 7 of the 9 are. The other two drive the motor at
> up to 80VDC @ 20A. This is clearly beyond simple signal switching,
> and I don't have the experience in power circuit design to figure out
> how to proceed.

maybe contactors (relays) will be best, you won't need to switch rapidly  
and very often?
Watch inductive kickback from the motor with any sort of switch, but  
contactors are most tolerant to abuse.
Also make sure you don't kill the drivers, some stepper drivers like to  
die if you disconnect the motor.

> Another, perhaps simpler puzzler for me is how to take a 17VDC, 4A
> unregulated signal and produce both a 5VDC & 12VDC regulated signal
> from it. Presumably, it's a matter of finding suitable voltage
> regulator ICs, but even approaching a simple circuit like this
> completely solo has me a little nervous.

Yes, regulators, either linear or switching, depends on how much current  
you need etc..

> I realize this forum might not be the right place to post such
> questions, so what is the appropriate place?

This is xactly the right place.


ST