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From: firstname.lastname@example.org (Mike)
Subject: Wanted: comparator circuit design
Date: 28 Oct 2002 13:16:59 -0800
NNTP-Posting-Date: 28 Oct 2002 21:16:59 GMT
I have a linear actuator which incorporates a 1Kohm potentiometer
which indicates the relative position of the arm. Fully retracted it
reads about 900 ohms and fully extended it reads about 200 ohms.
I want to wire up some comparators and logic to automate the shut-off
of the motors which extend and retract the arm.
There is a separate power lead on the motor for each direction (120V
I would like to incorporate the following:
1) An "extend limit" potentiometer; this sets the upper limit at which
the motor stops when extending (example: set for 890 ohms).
2) A "retract limit" potentiometer; this sets the lower limit at which
the motor stops when retracting (example: set for 210 ohms).
3) A momentary "extend" pushbutton, which when pressed, will apply
power to the extend motor, until the actuator potentiometer reaches
the limit set in 1) above.
4) A momentary "retract" pushbutton, which when pressed, will apply
power to the retract motor, until the actuator potentiometer reaches
the limit set in 2) above.
5) A momentary "stop" pushbutton which will disable either the extend
or retract motor, if running, prior to hitting the above limits.
6) Pressing "extend" while already retracting or "retract" while
already extending would cancel the current movement and begin movement
in the chosen direction.
I know this can be accomplished with a few comparators, some logic
gates, and some latches.
The motors draw under 1 amp; it would suffice to switch them via a
relay driven by the logic output, although a solution using a triac or
similar would be all the better.
Any ideas greatly appreciated!
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