On Fri, 22 Jun 2007 19:58:35 +0100, "Cableguy" wrote:
Thanks for all of your inputs...
My project is to motorize a compartiment door activated by a single button
like "open/close".
Since DC motors are alot more inexpensive and I have afew of them around
from slot-cars, Speed is not an issue, of course the more smooth the
moviment the better,
I've tryed to buil a "relay logic" circuit but got stuck in the midle and
eventually dropped that concept...and turned to uP....I was planing to use
PicBasic since I do some Basic related programing in Windows and WIndows
Mobile enviroments....
The movements should be like this:
If on point A go to point B and stop
If on point B go to point A and stop
If in between go to point A
Position would be determine by either micro-switch or integrated IR
barriers....I dont know waht sp+pecs to search in order to choose a uP so I
was counting on Your input and experience...I figure I only need 5 I/O pins,
and the code should be that big either...
Well that would be a perfect relay logic application so that's what I
would use.
What you want is simple (keep it simple). In the old days they called
it "zero seeking."
For instance you turn on a motor and it revolves a platter (opens a
valve, moves a chain, moves something) and it rotates until it reaches
a switch that turns off the motor.
That is "zero seeking." in its basic form. Windshield wiper motors
use it today so they stop at the bottom of the stroke when power is
removed.
You have two positions you want to access and a default position to
goto when it starts up in between stations. (presumably it would be
at A or B most of the time unless something outside intervened).
You are probably familiar with those single pole double throw
switches? (from electronics suppliers or hardware stores to control a
light from two locations?)
Well, in its simplest iteration you would transfer power to one or the
other limit switch and have it move the motor until that switch was
"satisfied" (actuated - normally closed then opened by the motor or
gearing) whereupon it would switch off power.
move switch to A motor goes to A then stops. Ditto B.
NO microprocessors works with AC or DC and no electronics.
Now you also want it to goto A when in between - the in between a
power failure or something physically moved it despite the motors
wanting to return it to the desired location???
The power failure senario can be done with two relays. One comes on
with applied power (assuming that's how it got between stations) and
runs to A until it energizes a second relay that stays energized
dropping the first relay out of the circuit and latching in that
state.
If, for some reason you want it to do all that and you have
over-riding clutches or can physically overpower the drive mechanism
resulting in an in-between state you could use a PICAXE
microcontroller to do that for about $3 plus $10 in cabling to program
it - then you could add delays, and have it make decisions based on
time or other inputs.
So I come back to my earlier statement; you should just tell us what
you want to do and that will determine the best way.
Don't jump into a programmable device as the first solution you try -
they offer a lot of versatility and lots of options for later change -
but if you only want to do one thing - the simplest way is often the
most reliable way and that could be the lowly relay. (no special
power supplies, no power up reset hassles, less/no interfacing
circuitry, better noise immunity, etc.)
A Programmable Controller can always be added later.
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