Relay question for Raspberry pi

[pvr]

Planning a bit of a project over Christmas to use a Raspberry pi with an ANPR camera to switch my gates when my plates are recognised.

Would this work to switch the two cables that are used for the intercom system now?

The wires are described as: "they require a pulse of a normally open, volt free contact to open the gates"

For the cost of the Pi and the connection to my LAN, it opens a lot of features of remotely opening the gates from my PC or iPhone, just some Christmas fun for the price of a single remote 

[X5Sport]

If I'm reading this correctly, your gates use a 0v signal to open and a constant voltage on to remain closed yes?

Probably worth checking this with a meter to ensure you know how long the 0v 'pulse' lasts.

If all it needs is a momentary 'drop' then it should work.  If it needs a longer pulse then the Pi can no doubt be programmed to extend the 0v pulse length before returning the system to volts on again.

Richard

[pvr]

Not sure yet Richard, when I emailed the company that is what they emailed back.

There are two wires that used to be connected to the intercom system that failed after a couple of years. The replacement was quoted at about £2k so passed on that rather quickly.

Holding the two wires together is supposed to open the gate. Keep holding them together that is the time they will remain open.

So I am planning to have a pulse check first of say half a second to just open the gates after which they close after the normal time has passed. Then I want to test to open the gates for say 10 minutes (some people take forever to leave and I keep having to press the remote to keep the gates open as they try to close after 30 seconds or so normally).

[Steamyrotter]

Volt free meaning that the relay does not supply the voltage..

ie acts just like a normal switch between the 2 wires the gate control supplies....

[pvr]

Ok, so I only need to have sufficient power to make the relay switch and once the contact has been made, the connection will be done and the gates will function without putting stress on the Pi.

Never worked with one before, but it is unbelievable what can be done with these things and for really no money what so ever.

[Steamyrotter]

Basically yes.
The PI will switch the relay coil (Via whatever circuitry to protect the pi GPIO circuits) which changes the state of the relay contacts.

These then provide the connection to the gate (ie simulates you holding the two wires together.)

My concern is that it may close on you when you dont want it...
Has your system got vehicle detection?  ie break beam sensor at the gates, or proximity detectors??
If not then i would propose you add them into the PI program.

PI s are great.
Been playing with one for a while, but nothing too indepth at the mo.

[pvr]

The gates have all the security in place with 3 sets of beams that keep them open when you break them, so nothing changes.

It just adds to the existing normal remote controls, and as I had a stupid quote for the intercom replacement (£2k), I thought I would go for an alternative approach and have an excuse for some play time over Christmas which does not resemble my normal day job.

If I get it all up and running, the gate automation company is interested in looking at it so might be able to flog some of them.

[X5Sport]

[quote="Steamyrotter"]
PI s are great.
Been playing with one for a while, but nothing too indepth at the mo.
[/quote]

Let me guess, you're building your own DME/DDE and gearbox controller...... O:-)

Richard

[kjb1]

bit of a security issue with anpr in that anyone who is aware of the system could easily knock a set of plates up etc?


Sent from my iPhone

[pvr]

That sounds like a lot of work whilst they can just rip out the gates with a 4x4 if they so desired anyway ….

[X5Sport]

And you'll need extra locks if the system recognises 535dboy.......

[X5Sport]

[quote="pvr"]
That sounds like a lot of work whilst they can just rip out the gates with a 4x4 if they so desired anyway ….
[/quote]

Simple with a laser/inkjet printer.  Any word processor could get the text right.

A 'smart' tag would be better.

[535dboy]

[quote="X5Sport"]
And you'll need extra locks if the system recognises 535dboy.......
[/quote]

I have a fob to get in anyway for those times he is away so i can service Mrs PVR.

[X5Sport]

[quote="535dboy"]
[quote="X5Sport"]
And you'll need extra locks if the system recognises 535dboy.......
[/quote]

I have a fob to get in anyway for those times he is away so i can service Mrs PVR.
[/quote]

Now you just need to hold up a print of his number plates...... )

[pvr]

Nah, he will be out of there again before the gates have even closed yet.  )