Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!uw-beaver!tektronix!tekcrl!tekgvs!tekirl!johno
From: johno@tekirl.LABS.TEK.COM (John Ollis)
Newsgroups: sci.electronics
Subject: Re: Mechanical actuators
Message-ID: <5448@tekgvs.LABS.TEK.COM>
Date: 26 Jun 89 17:17:05 GMT
References: <1436@xn.LL.MIT.EDU>
Sender: nobody@tekgvs.LABS.TEK.COM
Reply-To: johno@tekirl.LABS.TEK.COM (John Ollis)
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Organization: Tektronix, Inc., Beaverton,  OR.
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In article <1436@xn.LL.MIT.EDU> rsteele@LL-XN.ARPA.UUCP (Rob Steele) writes:
>I need a mechanical actuator to operate under microprocessor 
>control.  Ideally it would be a solenoid that works off of 
>5 VDC and not much current.  The thing will be pulsed at
>around 7 Hz. with a 50% duty cycle and need not exert much 
>mechanical force.  Am I dreaming?  What alternatives should
>I know about?

Several years ago, I worked on a driver for a solenoid actuated Selectric
typewriter running at as much as about 15 Hz, so I'd say the speed you want
is possible.  I don't know what your background is, so I'll warn you about
something that you may already know about.

The coil of a solenoid is an inductor and doesn't like to have the amount
of current flowing through it change.  So when you attempt to turn the coil
off, it produces a whole lot of voltage and probably burns out any circuit
you are trying to drive it with.  A common technique to prevent this is to
place a diode across the coil such that the diode is reverse biased while the
coil is turned on.  Now, when you turn the coil off, the current will flow
through the diode until the energy is dissipated.

Depending on the type of solenoid you select, you may want to look at a driver
chip such as something from the TI SN754XX family of drivers, some of which
already have the diode (they call it a clamp) built in.  See the TI Interface
Circuits Data Book.  You can also build a driver yourself with transistors and
stuff, but it seems easier to buy one that's already together.

I hope this rambling will be some help to you.

John Ollis
johno@tekirl.LABS.TEK.COM