Air Assist Control via Gcode

[Stefan Hechenberger]

So adam reminded me that the air assist pins need some extra work (they
are used to switch compressed air and/or nitrogen directly from gcode
M7, M8, M9). The current state is:

- the pin block grn-3.3V-A4-A5 is mislabeled. It should be
A5-A4-3.3V-grd (http://www.flickr.com/photos/stfnix/6831337649)

- the air assist pins A4 and A5 are normally high and low when
activated. We will most likely inverse this with the next firmware
update so that calling M7 and M8 sets the A4 and A5 pin high. M9 then
set both low.

- docs don't include any solenoid valve wiring recommendations


Questions:
----------

- what kind of solenoid valve should we design for. Normally open or
normally closed?

- What's a good connection circuit for solenoids (they produce a lot of
noise and draw significantly more than the arduino's 40mA per pin):
transistor->relay->solenoid? mosfet, diode? solid state relay?


--
Stefan Hechenberger, Nortd Labs
http://labs.nortd.com | http://blog.nortd.com

[jet]

On 6/25/12 19:48, Stefan Hechenberger wrote:

> - the pin block grn-3.3V-A4-A5 is mislabeled. It should be
> A5-A4-3.3V-grd (http://www.flickr.com/photos/stfnix/6831337649)

Ah, so that's why our relay clicked on and stayed on while power was
applied...

> - what kind of solenoid valve should we design for. Normally open or
> normally closed?

I'd say normally closed as that seems to be the "off" state for what I use.

> - What's a good connection circuit for solenoids (they produce a lot of
> noise and draw significantly more than the arduino's 40mA per pin):
> transistor->relay->solenoid? mosfet, diode? solid state relay?

I set this up today for SCI using this relay:
http://www.sparkfun.com/products/100
and an automation direct 24V solenoid

24V gnd
| ^
V |
Arduino pin -> relay -> solenoid
Arduino gnd -> relay gnd


--
J. Eric Townsend, IDSA
design <http://www.allartburns.org>
hacking <http://www.flatline.net>
fabrication <watch this space>

[Stefan Hechenberger]

The relay draws 37.5mA? Nice.

This is probably just simpler than using FETs and diods like this:
http://arduino.cc/playground/Learning/SolenoidTutorial

Stefan Hechenberger, Nortd Labs
http://labs.nortd.com | http://blog.nortd.com

[Trevor]

Thank you for clearing this up for us Stefan. We ended up using a transistor with a flyback diode to switch our valve, also a 24V normally closed valve. I would say that transistors would be the cheapest route, but that relay Eric posted looks like a pretty good buy. I guess the one benefit of using a transistor is that it would take up less space on the shield if we ever wanted to integrate the air assist control circuit into the shield. We will post up some pictures and diagrams of our control circuit tomorrow, as well as specs on the valve and regulator we are using.

Cheers!

- Trevor

[jet]

Shield space is the last thing I'm worried about given the physical size
of the Lasersaur. :-)