[TriEmbed] Transistor as switch

[Carl Nobile]

Van,

My concern with getting this to work for Brian's class is that there may be
a lot of RPi's that blow up if he goes the seemingly "good enough" route.
Even using a relay without some opto isolation may cause smoke. There is no
"good enough" when talking about inductive loads. One needs the minimum
requirements in all cases or you'll be hearing crackling sounds and a
little fog afterwards.

Carl


On Mon, Jun 15, 2015 at 10:59 PM, Van Watts via TriEmbed <
triembed at triembed.org> wrote:

> Guys, interesting discussion to me because I have been recently
> learning about motors and motor drivers for projects at work.
>
> Maybe i'm wrong but im not sure I heard it answered whether Brian's
> proposed transistor is likely to be "good enough" for his class for
> kids--or is it more likely to blow up his RaspberryPi?  As it is, his
> class is coming up very soon.  And I know how "perfection is the enemy
> of good enough" when you're running up on a deadline!
>
> Also, a distinction I just recently learned (and someone can correct
> me if this is wrong):  Back-emf (bemf) is the positive voltage
> generated by a spinning motor (think "generator"), while fly-back
> voltage is the negative voltage spike generated by the motor
> (remembering that a motor is a big inductor) when the power to it is
> suddenly cut and the magnetic field collapses.  Both need to be
> considered but take different forms and take different means for
> handling them.
>
> I learn a lot reading y'all's posts. :)
>
> Thanks!
> Van
>
>
> Sent from my iPhone
>
> > On Jun 15, 2015, at 9:00 PM, Jon Wolfe via TriEmbed <
> triembed at triembed.org> wrote:
> >
> > When I decided to get into electronics, and learn the pragmatic "get it
> done" approach as opposed to the electrical engineering electives I was
> forced to take in college, I found the "robot building" series of books by
> David Cook really well done. I know he covered making your own h bridge
> motor drivers from basic discrete transitors,  and how they work. I know I
> did the exact same thing in labs in colllege, but the presentation was so
> different it was enjoyable to learn.
> >
> > -------- Original message --------
> > From: Grawburg via TriEmbed
> > Date:06/15/2015 8:02 PM (GMT-05:00)
> > To: triembed at triembed.org
> > Subject: Re: [TriEmbed] Transistor as switch
> >
> > The basic electronics book the student get (Make: Electronics (Learning
> by Discovery)) doesn't cover MOSFETs so I can't use them for this segment.
> However, later on this summer I have another class and will introduce them
> then. I do need to think of a good low-cost project that basically is a
> "proof-of-concept" project and not an actually a big project.
> >
> > The opto-isolated relays I used for my conveyor/train humpyard are what
> we'll use this time. Safe and easy to set-up.
> >
> > Don't know what I'd have done with the Raspberry Pi had I not found
> TriEmbed!
> >
> >
> > Brian
> >
> >
> >
> >
> >
> >
> >
> >
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-- 
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Carl J. Nobile (Software Engineer)
carl.nobile at gmail.com
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