I've looked at RFID from time to time but lately it has become more appealing to me, so I thought it would be useful and interesting to see what folks are thinking about doing with them. Jeremy did one on a recent bike, and there are undoubtedly a few others out there.
Just to pick up those folks who don't know much about it, RFID stands for Radio Frequency Identification. These "tags" send out a unique code that can be used as an identification key. The smallest and lowest cost devices are generally powered remotely by the tag reader so they don't have internal batteries. (There are other types).
They work by the tag reader sending out a magnetic field which charges up a small energy store in the tag, then the tag can transmit its message. So the reader needs to either send out pulses all the time, or know when a tag might need to be read. The amount of power the reader consumes is related to the range of detection, it takes more power to energize a tag farther away.
Some folks have proposed putting the reading antenna (a coil of wire) under the bicycle seat (Jeremy did that, as I recall). This is a good place for one, though detecting it in the user's pocket may not work out well due to the limited range of most readers being a few cm. but if you can insure the tag gets read that would be a good spot, safe and out of view.
On my Greyborg there are plastic covers on the batteries that would be excellent to read through, the 'antenna' is a coil of wire that could be placed inside the plastic. The tag could be on a keyring or in a glove or a band around the wrist or glove. Implementing an RFID tag is probably easier than a keyswitch in some sense due to the difficulty of mounting a keyswitch in a convenient place on a bicycle.
I don't want to operate the tag detection system all the time as that consumes power. On my bike I have a kill switch that cuts power to the controller, so one simple design is to have the tag reader come on with controller power and set things up so the throttle is shorted or the ebrake is activated until the tag reads successfully. Then the tag lock releases the throttle/ebrake and shuts down the reader to conserve power until the next time power is cycled. When power comes on it powers up and locks the throttle/ebrake waiting for the unlock tag again.
There are many other ways this can be done.
The tags Jeremy used and I have ordered are 125 khz em4100 type. There are a number of different frequencies and types. Make sure the parts you select are compatible. Some RFID systems have a lot more capability that you probably don't need, such as programmable keys, etc.
Tag reader boards cost from $10 on up, many tags are under $1. Tags come in various styles such as credit card type, key fobs, sterile waterproof glass tubes, and more. So you can carry one on your keyring, and a backup in your wallet. You may even have such a card for accessing doors at work that you may be able to read and use as a backup key.
The data stream from tag readers can be USB, serial or a simple pair of pulsed lines for "0" and "1". It is fairly simple to read this into a microprocessor and check the value for an "approved" key code. Since each tag has a different code the reaction to different tags could be different - for example the speed or power level could change. A little Arduino or Picaxe can easily handle the job.
A note to Justin - an RFID reader in the Cycle Analyst would be a nice touch. Could be a killer app for ebike security. Perhaps even an option for a code access to have a low budget solution. The CA has access to clamping the throttle so it is an easy upgrade.
So what are folks doing with RFID, and what other great ideas do folks have?
http://en.wikipedia.org/wiki/Radio-freq ... tification
http://www.seeedstudio.com/depot/electr ... Path=48_52
many readers and tags on eBay