[TriEmbed] Question concerning a mechanical release

[Scott Hall]

Actually the typical circuit, from a Pi or any other controller, consists of a
NPN transistor, driving a MOSFET, which drives the solenoid.  Hard lesson
learned from years of model trains and diorama animations.  I have seen people
drive the solenoid directly through a single transistor, but like you said, you
gotta watch for the back EMF current.

Basic Relay or Solenoid Driver

See this article:
http://www.delabs-circuits.com/cirdir/electric/discrete/del50010.html

Here is an article of a simpler circuit:
http://electronics.stackexchange.com/questions/62415/solenoid-driving-circuit
schematic

Here is an Instructable:
http://www.instructables.com/id/Controlling-solenoids-with-arduino/

And this EE claims that others do it wrong, and he uses proper EE analysis to
prove it: http://www.evdl.org/docs////solenoid_drivers.pdf

On 09/24/2013 11:31 AM, Rodney Radford wrote:
> If only controlling the release of ball bearings on a track, the simplest
> approach may be a single R/C servo with an attached wand that can be
> controlled to lift up, let the ball roll through, and then drop to catch the
> next ball (I assume there is more than one).
>
> And yes, it is possible to control *one* R/C servo on the Raspberry Pi without
> additional hardware using the PWM channel (lots of references online via google).
>
> The idea of the solenoid will also work, but the spikes from a solenoid can be
> rather nasty, so there will need to be some isolation between the RPi and the
> solenoid.  I would not recommend using the 3.3v or 5v supplies through the
> RPi, and you should put a diode across the solenoid to help ease the spikes
> when the solenoid returns back.
>


-- 
Scott G. Hall
Raleigh, NC, USA
ScottGHall1 at GMail.Com

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