[dorkbotpdx-blabber] where to get and learn about solenoids

[Greg Grunest]

Greg,

An opto isolator looks like a led and a phototransistor in the same sealed
package.  You drive the LED from one of the Arduino ports, just like you do
for the built-in pin 13 LED.  Turn it on, turn it off, etc...  The
phototransistor "sees" the light emitted from the LED and turns itself on
and off in turn, acting like a switch.  You can switch much larger currents
and different supply voltages with the phototransistor this way.  It's
called an optoisolator because at that point, the two sides of the circuit
(the LED side, and the phototransistor side) are "optically isolated".  It's
cool because you can have massive (not really too massive) voltage spikes
and current draws on the phototransistor side of the circuit and the
microprocessor, sitting on the LED side, will never even know it's going on.

Another cool thing I forgot to mention is that it's a super easy way to
allow a microprocessor to control line voltage.  You can switch 120V AC with
this device.  BE WARNED THOUGH!!  Messing with 120V AC can and will hurt
you.  It *WILL* blow up your Arduino.  It *WILL* eventually send you flying
across the room and lighting your underwear on fire.

Don used one on his most recent music board for the Arduino in the cult
induction class.  I didn't look at what it was or where he got it from but
he might be a good person to ask.

- Greg Grunest





-----Original Message-----
From: dorkbotpdx-blabber-bounces at dorkbot.org
[mailto:dorkbotpdx-blabber-bounces at dorkbot.org] On Behalf Of Greg Borenstein
Sent: Tuesday, December 02, 2008 11:49 PM
To: A discussion list for dorkbot-pdx (portland, or)
Subject: Re: [dorkbotpdx-blabber] where to get and learn about solenoids

Greg,

That was really helpful! I'd love to take you up on that offer for the  
rotary solenoids if you've still got them. Any leads on where I can  
look to learn more about "opto isolators"?

-- Greg

On Dec 2, 2008, at 11:38 PM, Greg Grunest wrote:

> Greg,
>
> Solenoids come in all different varieties.  Typically, you find the  
> 12 V,
> linear, push or pull solenoids in everyday consumer electronics (disk
> drives, hard drives, tape players, that old and now useless Zip-100  
> drive
> has a really cool 6v one in it but it's *really* hard to get it out,  
> etc...)
> but every so often you can find surplus rotary solenoids too.  For  
> moving
> the drumsticks, a rotary solenoid might be the thing.  They  
> typically move
> through a 90 degree arc when energized and then return to where they  
> started
> when power is removed.  However I've had some before that sort of  
> ratchet
> through 15-30 degree increments each time power is applied eventually
> spinning all the way around.  They were connected to a little  
> mechanical
> counter and appeared to do nothing more than count how many times  
> this thing
> had fired.
>
> The pros:
> 	They're cool!
> 	They typically work forever - millions of cycles.
> 	You can do things with an $8.00 solenoid that you could otherwise
> spend hundreds of dollars trying to replicate.  (I once built a remote
> controlled golf cart and used Ford starter solenoids ($8.00 from  
> Napa) to
> switch the 600 Amp battery connections to the motor.  I used a $3
> optoisolator to drive the solenoids and an 8051 to drive the  
> optoisolator.
> Controlling 600Amps from a microprocessor for $11 - Woot!)
> 	You can get feedback from them by measuring how much current they
> draw (voltage drop across an in-line resistor) and tell if they are  
> hitting
> anything.  They tend to draw a lot of current (like a stalled electric
> motor) if you hold them against their will.
>
> The cons:
> 	They suck current like mad and therefore are not good for battery
> driven applications.
> 	It's basically a coil so you have to worry about re-induction when
> the magnetic field around the coil collapses so you don't blow up  
> sensitive
> circuitry (like the Arduino or a transistor).
> 	They are typically not driven by any control signal that is easy to
> generate in a microprocessor world, 9-50V, 500ma-2A.
> 	(Because of these two drawbacks, I highly recommend a simple 8 pin
> optoisolator to drive them.  It's cheap and completely protects the
> Arduino.)
> 	You can't control how fast they move like you can with a servo.
> They are either in or out, turned or not.  In fact, if you try to  
> slow them
> down by limiting the voltage they draw a LOT of current.
> 	They are entirely digital - On or off, in or out.
>
> 	And the number one drawback is........ can you say "latch up"?
> (sometimes they stick in the "energized" state.)
>
> Just my 2 cents.
>
> BTW:  If you're interested, I think I have a couple of the 90 degree  
> rotary
> ones left.  Enough for you to play with and try the drums anyway.
>
> - Greg Grunest
> greg at grunest.com
>
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