Re: need HELP with a high school prom project PLEASE!!!!!

["Robert L. Bass" <robertlbass@xxxxxxxxxxx>]

> ... I need a way to make it stop at the
> bottom, wait 2 -3 minutes and then
> reverse the DC current...

Piece of cake, Rudy.  This can be done using relays, timers and sensors or
more elegantly and for a little bit more money using a programmable
controller like the ELK-MM440 (aka "Magic Module").  Note: I sell these so
I'm not exactly unbiased, but choose for yourself how you want to accomplish
the task.

The Magic Module has inputs which you would connect to inexpensive magnetic
sensors (contacts) of the same variety commonly used to protect doors or
windows in an alarm.  Mount sensors at the top and bottom of the pole.
Place magnets where they will trigger the sensors as the ball approaches.
Use one relay to interrupt power any time either input is tripped, wait 2
minutes and restore power.  Throw a secondary DPDT relay with another of the
MM's outputs to invert the DC power whenever the top input is tripped.
Release these relays when the bottom input is tripped.

This will cause the motor to raise the ball upon power-up, wait two minutes
at the top and start the descent.  Upon reaching the bottom the ball will
stop, wait two minutes and begin another ascent.  If this sounds too
complicated it's only due to my poor communication skills.  It's actually a
very simple circuit to build.

If you don't want to spring for the ELK Magic Module, you can do pretty much
the same thing using dumb timers and relays, either from ELK or Altronix.
The difference will be around $1C.

--

Regards,
Robert L Bass

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