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An example EtherTen application - PoE RFID access controller

Posted: Thu Dec 20, 2012 4:35 am
by LukeW
In this video, I've used an EtherTen from Freetronics to implement a RFID security controller which operates a solenoid door strike.

(For this video, a solenoid valve is used as stand-in for a door strike solenoid, since I don't have one of those in stock right now, and the valve will have similar electrical characteristics.)

Green LED (and solenoid actuation) means access is granted, whilst the red LED means that the RFID tag presented is not an authorised one. When the green LED changes state you might be able to hear the click of the solenoid actuating - but it's barely audible in the video.

I used a Freetronics Protoshield Short to put together the very simple circuit required (basically just an open-drain FET that drives the solenoid, plus a RGB LED for user feedback and debugging, and some resistors to glue everything together properly. There are also a couple of spare pins on the solenoid header, these are for a "detect when door is open" switch.

However, you don't really need to build the circuit from scratch yourself... you could use a Freetronics RFID Lock Shield, which is basically the same thing all ready to go with minimal assembly.

Power is supplied to the system via Power-over-Ethernet, so you don't need lots of cables running everywhere - just ethernet and a couple of wires to the solenoid.

I don't have an 802.3af switch (and it's hard to use both a Protoshield and a 802.3af regulator board with your EtherTen at the same time without fabricating a custom-designed PCB instead) so I just used simple "hacker-style" non-negotiated PoE injection at 12 volts after an unpowered switch. (You could do the same thing in a much neater, easy way with a Freetronics PoE Midspan Injector board.)

The only small disadvantage here is that at a 12V input voltage the EtherTen's LDO will get a little bit warm, but it works perfectly well and isn't a problem.

The beauty of using an EtherTen here as opposed to a standard Arduino is not just limited to minimalistic simple cabling, though - now the whole system is connected to the LAN, so with the right programming (I haven't gotten to this bit yet) it can all be administered and controlled remotely, via a web browser for example.

For example, you could "buzz in" a visitor who comes to the door but who doesn't have an RFID card, right from your desktop without walking over. You could edit the database of allowed RFID tokens, to add new allowed users or remove them, from any remote computer, making for convenient, easy administration compared to having that list written into the Arduino's program.

(Alternatively, you could just store the database of allowed users in a file on a micro-SD card in the EtherTen's microSD slot, and remove that card and just plug it into a PC if it becomes necessary to update the access list.)

Re: An example EtherTen application - PoE RFID access contro

Posted: Mon Dec 24, 2012 1:37 am
by ngp99
That water valve looks quite interesting and has given me an idea. Where did it come from?

Re: An example EtherTen application - PoE RFID access contro

Posted: Tue Dec 25, 2012 4:22 am
by LukeW

This is the solenoid valve I had laying around as shown in the above video, which is designed for 12VDC operation.

You can also commonly get solenoid valves intended for garden watering automation from shops such as Bunnings (or whatever your local equivalent is if you're outside Australia.). However it's important to note that these solenoid valves are commonly designed for 24VAC operation, so you'll need a relay (or maybe a Triac, if you're like me and you prefer solid-state silicon switches instead of relays where practical) to switch the 24VAC to the valve. A MOSFET or BJT won't work properly because it's AC.