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[on:]

Hi,

We want to build an air cannon for this Halloween.  Basically, air gets stored in a tank and released in a burst by a solenoid.  The idea is to give the Arduino an eye with a PIR motion sensor, and use it to trigger the cannon.  Here is a drawing of what is planned: 


I think this will work, but my specific question is on the relay.  It is this relay:
http://www.opto22.com/site/pr_details.aspx?cid=4&item=ODC5
and I'd like to get an opinion on whether that relay will get the job done.  I think it will but I don't know.

Any other opinions about the project as a whole welcome of course (especially if you have done something like this already!), but I'm really focused on relay at the very moment.

Thanks is advance,

Mike

[Reply #1 on:]

Looks reasonable. I'm not sure the TIP120 is necessary. For a short-duration burst, why not just drive the relay input directly from an Arduino pin? It can handle 12mA.

You could simplify the system by using a single 12V wall-wart, 12V solenoid, powering everything off the same supply, and using your TIP120 to drive the air cannon instead of the relay (it doesn't really *need* to be isolated). A simpler system is a system more likely to work

--
The Aussie Shield: breakout all 28 pins to quick-connect terminals

[Reply #2 on:]

Yes that should work fine, the coil only draws 12ma according to the data sheet, so you really don't even need the transistor on the output of the Arduino. Arduino output pins can withstand 40ma. Don't forget to put a diode on the solenoid as well.

**Wow rugged circuits must have answered as I was answering. Oh well, you get the point.

[Reply #3 on:]

Yes that should work fine,

Cool.  I was hoping I had at least some idea of what I was doing.  LOL.

the coil only draws 12ma according to the data sheet, so you really don't even need the transistor on the output of the Arduino. Arduino output pins can withstand 40ma.

Trying to be safety boy.    All the stuff I read had me switching things like this with a transistor to get the full voltage of the circuit on relay coil.

Don't forget to put a diode on the solenoid as well.

Thanks for that.  Noted.

You could simplify the system by using a single 12V wall-wart, 12V solenoid, powering everything off the same supply, and using your TIP120 to drive the air cannon instead of the relay

Well I had been looking at a solenoid like this one:
http://cgi.ebay.com/1-2-Electric-Solenoid-Valve-24-V-DC-Air-Fuel-B21N-/290538398689?pt=LH_DefaultDomain_0&hash=item43a57023e1
I hadn't see a 12v one, but I will have to look now.  I've never worked with them before and don't really know.  I was trying to match up with what I see in the Air Cannons for Dummies video on YouTube.

The idea was to make that cannon driven by the motion sensor/Arduino.

[Reply #4 on:]

I see a 12v now that I look.  Hmmm.  Interesting idea.

[Reply #5 on:]

Have fun. I built a ground breaker last year with an Arduino. I love Halloween.

[Reply #6 on:]

Any other opinions about the project as a whole welcome of course (especially if you have done something like this already!), but I'm really focused on relay at the very moment.

If the end product involves persons other than you, a review of your insurance coverage might be a good idea.

[Reply #7 on:]

Any other opinions about the project as a whole welcome of course (especially if you have done something like this already!), but I'm really focused on relay at the very moment.

If the end product involves persons other than you, a review of your insurance coverage might be a good idea.

Seriously THIS. I can just imagine some JD coming along, and when your back is turned he stuffs some dirt or sand or rocks in the tube, then the next unfortunate victim comes along and...

/not a pretty sight 

[Reply #8 on:]

Any other opinions about the project as a whole welcome of course (especially if you have done something like this already!), but I'm really focused on relay at the very moment.

If the end product involves persons other than you, a review of your insurance coverage might be a good idea.

Good thought (and thanks for that), but hopefully not an issue.  I don't anticipate it would ever operating in a completely unattended state.  I will be lurking about in the background.  The idea is to hide it in a trash can right by the front walk so that it surprises unsuspecting trick-or-treaters with a nice puff of air up their little costumes.

With any luck we'll use the same air source to drive a trash can trauma and have quite the little startle fest.

[Reply #9 on:]

I'm here to tell you that if you start messing with other peoples unsuspecting children (here in the US) in such a way, you may well end up in jail for simple assult and worse. You might lose your house and more in a civil action if the child becomes injured in response the fright reaction you caused him/her. A scraped knee or dust puffed in to an eye can be big $$$. Ask your insurance agent if this is covered under your homeowners policy.

[Reply #10 on:]

Thanks for your concern.