Cableguy wrote:
Default, Thank You very much for you input, with it I learned the "Zero
Seeking" term...

What I want to acomplish is a movable faceplate for a car audio system that
would Act when the power was feed to the circuit and then return when
powered off.

Like this.

car key in On position go from A to B and Stop
car key in OFF position go from B to A and stop

I havent yet startred the face plate movement design because I havent yet
decided how far the movement should go, althought taht is not important to
the circuit design...

Once again Thank you for your input...


Paulo Gomes



A single DPDT relay should do it for you.

+12 Accessory ----[Ry1]----------+-- Gnd
|
Ry1-1 / |
+12 ---+---o-o---o o---o o---+
Batt | O_Lim | | C_Lim |
| | |-' |
| | |
| o |
| | |
| [Motor] |
| | |
| o |
| | |
| ,-| | |
| | | |
+---------+ +---------+
Ry1-2

Shown in the closed position with the C_Lim (close limit) switch
open. When the car key is turned on, the accessory line goes to
+12 and the relay is energized. +12 from the battery gets to the
top of the motor through the Ry1-1 open contact and the O-Lim
(open limit) switch. (-) gets to the bottom of the motor through
the Ry1-2 open contact. The motor spins until the O-Lim switch
opens when the limit is reached. The C-Lim switch closes as soon
as the face plate moves away from the closed position.

When the key is turned off, Ry-1 de-energizes. This time, Ry1-1
_closed_ contact brings (-) to the top of the motor through the
closed C_Lim switch, and the Ry1-2 closed contact brings (+) to
the bottom of the motor. The motor spins in the opposite direction
from the previous operation, and continues spinning until the close
limit is reached, which opens the C_Lim switch. The O_Lim switch
closes as soon as the face plate moves away from the open position.

Ed