Use household 12 V DC adapter with RFID transponder?

Question

Is it possible to use a common household 12 volt DC output adapter with this RFID transponder. I am a newbie but I am willing to learn. Here is a diagram of this RFID transponder system of this.

http://i729.photobucket.com/albums/ww295/stealthmedal/6a2f9ff4.jpg

Wall wart:

The product description is as follows (for those in need of additional information) : The reciever operates on 12 VDC Details: The key fob is completely waterproof, and crunch resistant. Size:l.4" square and is meant to be attached to your keychain and has a recessed circle to allow you to place a custom label (if desired). The sensor is about 2.1" x 1.3" and is attached by 20" cable to the 4 1/8" x 2 1/8" receiver box. The sensor can be mounted in wood, behind glass or plastic and still function perfectly. The sophisticated receiver uses 6 ICs and have 12V OUT PUT WHEN TRRIGER . when the correct key fob is brought within 3 inches of the sensor. THE UNIT PUTS OUT 12V OUT PUT (MUST BE WIRED TO 12V REALAY), and when key removed from sensor relay will open.

Please help me.

Answer 1

If that's the drawing which came with the RFID reader, that's bad. It doesn't give me much hope for the details we really need to know. It should say what power the reader consumes, and what current the 12V output can supply. It suggests it can switch a relay, but that's useless. There are thousands of different relays, Digikey lists 1776 12V power relays. What load do you want to switch?
There's one which already switches at a 1.4mA coil current. I'm pretty sure you could use that, but it's a bit expensive. This one is inexpensive and needs 30mA, probably also within the ouput's possibilities. Depending on the version and type of load it can switch 5A to 10A.

The wall-wart says 12V 300mA, find out how much power the RFID reader needs, so that you know how much remains to power the relay. Then find out how much current the output can deliver. With this information you can select a suitable relay.

"I am trying to find out what these aspects of the drawing mean as well."

The red and the black wire are the 12V DC coming from your wall wart. They supply the power to your RFID reader. The relay is also 12V, and uses the same ground (that green line should also be black). The yellow line is the output of the reader, it switches between 0V (off) and 12V (on). So connecting a relay between that output and ground will switch the relay on when the output is 12V.

Answer 2

I have this same RFID reader (eBay) and can confirm that it will work with that DC adapter. I am a beginner myself, but that's the same input as mine (300 mA) and it works. The thing I'm having trouble with is wondering why you even need the relay in the first place if it's connected via a DC adapter to AC power? I thought relays were mainly used so batteries don't drain? Does this mean you wouldn't necessarily need one with this setup? I've used the RFID transponder to set off a small buzzer, and power a small LED, but once I connect the relay, nothing seems to work. I'm just not seeing the purpose of the relay in this setup (again, I'm a beginner and may be missing something pretty basic...)

Answer 3

Yes, however as kenny said, you need its current requirement. As user1299661 asked and Kellenjb asked above, the wall wart connects to -12 V DC in (positive) and what is labeled (-12V ground). I suspect -12V is "ground" for the +12 V DC in, not -12 V.

But again, check the manual for voltage and current required.