AVR-Chat

actually, im trying to drive a bolt thru the servo. the bolt will serve as a door lock. 
 
my problem is that if ever a brown out occurs, a simple switch on the back-up power will just power up the MCU and automatically turns the servo and drives the bolt to open. and then i would turn off the whole system to conserve power. but what if the door is already open when the brown out occurs? i know it would only require a single pulse value (2ms or 1ms) to turn the servo either way. and if it is already in a 180 degree angle, sending a pulse of 2mS doesn't really matter since the servo would likely to stay on the same position. 
 
and what if i power up the back-up power again so that the bolt will close? 
the problem now is that i should send a 1mS pulse for the servo to turn the other way.
that is why i should know the current position of the servo on power up for me to know the PWM value. and if possible, no more additional hardware for lesser power requirements.
thanks...
-jay
 
thanks for the help.

David VanHorn <dvanhorn@cedar.net> wrote:
At 08:05 PM 6/28/2004 +0000, Phil wrote:

>Some one did do just that.  check out this page - 
><http://www.portlandrobotics.org/robots/servo_encoder/index.html>
>
>but wouldn't an optical encoder simply tell you relative motion (not 
>absolute)?  

Depends on the encoder. Gray code or binary units give absolute, quadrature gives relative.

>How important is it to know the initial position?  You can command a 
>servo to a known position and go from there.  

Good point.


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