Cheap RFID interface


Staff member
Eventho it is back ordered, I figured I would post it here as it is pretty cheap.

Designed in cooperation with Grand Idea Studio, the Parallax Radio Frequency Identification (RFID) Reader Module is the first low-cost solution to read passive RFID transponder tags from up to 4 inches away. The RFID Reader Module can be used in a wide variety of hobbyist and commercial applications, including access control, automatic identification, robotics, navigation, inventory tracking, payment systems, and car immobilization. Features:
  • Fully-integrated, low-cost method of reading passive RFID transponder tags
  • 1-wire, 2400 baud Serial TTL interface to PC, BASIC Stamp® and other processors
  • Requires single +5VDC supply
  • Bi-color LED for visual indication of activity
  • 0.100. pin spacing for easy prototyping and integration
I've been watching those - waiting for them to be in stock.

Note that they are not 1-wire in the Dallas Semiconductor sense. All they mean by 1-wire is that you only need a single data wire to connect to it. The output is serial, like RS232 but not at RS232 levels. To connect to a computer, you will need additional (inexpensive) hardware.
hmm, I thought I just read somewhere that someone was ordering RFID hardware samples from Dallas Semiconductor, but can't find the site again. Thanks for clearing that up tho! I believe the site sells RFID equipment as well, would be nice to personalize certain experiences.
Looks neat.
Without looking at it close - this detector could be mounted in a wall and with a pass of a RFID device would be detected by the detector, data sent via a serial cable to PC, authenticated by the PC, and then an action like opening a door striker / disarming alarm / whatever could then happen?

Anyone look at the software side of it for how complex?

I assume being serial that the cable could be 100 ft? I was casually interested in the USB one that exists, but being USB the PC would have to be close proximity to the detector (impractical for my possible setup).

Anyone look at RFID device availability / pricing / form factor that would work with this detector? EDIT: I just checked - they offer them too (backordered). $2 per. Cheap! cool.

If the above is validated, I am a player to check it out. Homeseer plugin?
A functional HomeSeer script - no plugin required - would probably take (literally) less than 15 minutes to create. And then months to make "cool."

The Parallax device sends a 12-byte sequence (2400 8N1) when a valid tag is within range. "valid" means that it's a good code - it's not comparing it with a list of know codes. This is exactly what we would want.

The 12-byte sequence is a start byte, 10 id bytes, and a stop byte. The stop byte is 0x0D - very easy to check for in a script.

The script can be a standard HS com port handler. When you open the com port, you tell it to call your handler whenever 0x0D is received. The handler then needs to compare with a list.

By the way, this assumes that you don't have a 0x0D byte in the id list. If you do, you will need to put a little more effort into the script. Or, you can just make sure you never use an RFID tag with that byte in its id.

For entry control, etc., you can do a lot in that little script. Things like allowing a particular RFID to open a door between 9AN and 10AM on Tuesdays.

The output of the Parallax board is TTL-level serial. You need additional hardware to drive RS232. I'd skip RS232 on the reader end and go straight to RS485. Then you convert from RS485 to RS232 at the PC end. This would allow the reader to be (theoretically) up to 4000 feet from the computer.

The whole thing should be really easy to implement. So easy that it's probably not any fun to do. ;)
That's easy for you to say Smee. ;) For us electronic challenged types this could be a good learning project. I just can't figure out how the reader could be neatly mounted.
Rupp said:
I just can't figure out how the reader could be neatly mounted.
It's roughly 2.5x3.25 inches. It will fit behind a single-gang wall plate (but not in a standard single-gang box). No problem fitting behind a double-gang plate.

I wonder if there are smaller tags that are compatible. The round ones are about 2 inches in diameter.
It would be nice to have a key tag size RFID tag... Don't think I could get the wife to hang a 2" tag on her keyring...much less get one into my pocket.

Also, are the RFID tags they sell here compatible with the other RFID reader/HomeSeer Plugin that is being discussed here.. Much cheaper than the ones they are selling.
The other RFID tags (discussed on HS boards and here) are active and have a much larger range. The tags themselves are broadcasting their ids (they have their own power source, batteries).

The tags in the Parallax system do not broadcast their id. They are read by the receiver when they are in range (within 4 inches).
Would one be able to use the speedpass as the RFID tag, or would the encryption be an issue?
I wonder if you pass the "Speedpass" or other passive RFID device next to this reader, if you just trap the incoming data then you could put it on the "GOOD" list. encryption or whatever. As long as the second time you pass it by, you should get the same response, and it would validate as it's now on the GOOD list.
Does that theory pan out?

My house has cedar tongue and groove siding (vertical). I am thinking of taking one panel out (rip the tongue), cut on the backside a notch using a Dado blade, so that the detector can nestle behind the exteriour facade. Then, drill a hole for Cat5 wire, wire to the detector, place the detector where the siding notch would be, and put the siding back up. That would make it invisible to anyone who didn't know it was there. With just a pass of the RFID passive device near the wall, it would authenticate. Might put the device into a heavy plastic bag for additional weathertite (open to the bottom for ventilation / drainage).
electron said:
Would one be able to use the speedpass as the RFID tag, or would the encryption be an issue?
I have no idea what the encryption is on a SpeedPass, but I would assume it's a 'rolling-code' algorithm. If it's not, then it's not really secure.

The problem with a rolling-code algorithm is that the tag never sends out the same code twice.
How would a passive device implement a rolling code? Doesn't it need some kind of basis like date / time? Then again, how do garage door openers do it...

Smee - no excuse... I don't have a "need" for it either ;)