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Author Topic: Suggestions wanted for model guard/gate house  (Read 892 times)
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One of my hobbies is radio-controlled semi-trucks and as a project I want to build an automated guard house with an entry and exit gate that moves up and down by servo.  Since this is my first electronics project I'm looking for suggestions.

I know this could probably be accomplished without using a microprocessor, but I'd like to add more features later on if I get the gates working nicely.  I figure I could use a 'pressure' switch that makes the gate go up when the truck drives on it, but it's when to bring the gate down that is more tricky.  In the RC group I belong to guys have all sorts of trucks of various lengths, so I'm not sure about using a timer.  Also, how does a garage door detect that there is something in the way when closing?
I'm open to suggestions...  Thanks for your time.

Brian
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Also, how does a garage door detect that there is something in the way when closing?
Two different ways. One measures the current needed by the motor that moves the door. When that current is too high, it means that the door has hit something.

The other way uses an IR LED and sensor. The IR LED goes on one side. The sensor goes on the other side. When the beam is interrupted, something is in the way of the door, so it stops or won't start.

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One of my hobbies is radio-controlled semi-trucks
I've never seen an RC semi-truck. Got any links?
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I imagine they're scale models
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Yes I guess I should have mentioned they are 1:14 scale.  Here's a link:
http://www.tamiyausa.com/product/category.php?sub-id=35000
There are tons of videos on Youtube of RC semi and construction equipment.  Expensive but really fun to build and play with.
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Yes I guess I should have mentioned they are 1:14 scale.  Here's a link:
I assumed that they weren't full size.

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Expensive but really fun to build and play with.
I'll have to take your word on the fun part. The expensive bit was immediately obvious.
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I figure I could use a 'pressure' switch that makes the gate go up when the truck drives on it

You could use IR to accomplish this - send a command from the truck to an IR Receiver mounted on your garage door to open and the opposite to close it.
Just my 2 pence worth!
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Easiest way would probably be 3 IR beams of some variety, 1 before, 1 in the middle and one at the other side. If any beam is interrupted gate opens and stays open until all beams are clear. Full size automated gates work in pretty much the same way but use proximity loops rather than IR beams in some cases.
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@BrianS

You could use the pressure switch, detect the weight of the truck, the gate lift and stay there, at the same time , checking the pressure switch ( the weight of the trailer ), check again for weight , if no weight,  the gate still  stay open after, let say 10 second, and then the gate going down just like when you drive into a condo/apartment complex parking lot equipted with an automatic gate system.

My idea.

I check the link, Those trucks are so .... Nice & Cool... ( I wish I have one ). Expensive, Yes Specialy with 2 servo and a motor with 3 speed transmition gear box... Now THAT Cool ...Fun ... yes, specially backing up a trailer...That take skills...  I did drive a 18 wheeler truck in 2000 -2002 with 10 speeds - Learn to have my AZ licence ( Ontario ) in 2000.         
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@inboxjason:  Thanks for your reply and suggestion.  I'm sure your solution would work well if it was only my trucks I was concerned about, but I plan on using this guard house at club meetings and 'get togethers'.  So installing IR on everyone's truck wouldn't be practical.  I even considers using magnets on the truck and a reed switch to raise the gate but again everyone would have to install a magnet for it to work so I counted this idea out too.

@Lurch: Thanks for your suggestion.  With the IR beams you suggest would I need a sender and receiver?  Like an IR LED and a photodetector or reflector of some sort?  I think the 3 sensors you outlined might be the way to go.

@Techone:  Thanks for your suggestion.  Your suggestion is very similar to the way I thought about doing it, but just using an this-seems-long-enough value for the gate to stay open worries me.  In my club guys have all sorts of trucks with various lengths.  Some pull multiple trailers even.  So I'm afraid that 10 seconds or some number I pick might be too short if the driver goes too slow or is distracted.  I wouldn't want to damage their truck or my gate.  That's why I asked about how a garage door detects if something is under it.

Here is my latest thinking:  The guard house will have some sort of base (like plywood or MDF).  What if I drilled a hole in this in the middle of the roadway the right size for a photoresistor facing up.  Would a truck driving over it change the photoresistor's value enough to be detected?   I could use 3 of them as Lurch suggested (1 before, 1 at or close to the gate, 1 after)  Any thoughts?
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Here is my latest thinking:  The guard house will have some sort of base (like plywood or MDF).  What if I drilled a hole in this in the middle of the roadway the right size for a photoresistor facing up.  Would a truck driving over it change the photoresistor's value enough to be detected?   I could use 3 of them as Lurch suggested (1 before, 1 at or close to the gate, 1 after)  Any thoughts?

That could work, I'd be inclined to experiment first. You have to think about what the likely failures are of the design, could a decent set of truck lights fool it into thinking there is nothing there? IMO the most reliable way is the IR beams, transmitter and receiver. Could also double them high and low at each point so there is more likelihood of different trucks being sensed depending on wheelbase\trailer type etc...
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Ah if you have multiple trucks it could get very impractical. I think Lurchs' way would probably be the way to go. You could have three sets of IR beams, one outside the garage door, one under the garage door, and one safely inside the garage door, as a truck breaks the first beam, you'd open the door, the second beam would mean the truck was moving under the door, and the last beam breaking would mean the front of the truck was in the garage, then simply close the door when the second or last beam is back to it's unbroken state.
There is a good post about this on Ken Shirriffs blog.
http://www.arcfn.com/2010/03/detecting-ir-beam-break-with-arduino-ir.html
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