I can't remember if I've asked this before, but what the hell...

This is one for the electronics techies on the forum.

I want to make a security system for my car that works in a similar way to those in big posh Mercedes - if you have the transponder in your pocket the car will start, if not... no chance.

What I'm looking for is a clue to help me find the best technology; I can work out how to use it (that's part of the fun!). I don't want a commercial system as (a) they're usually expensive, and (b) they usually come with their own setup for wiring into the loom, and that's already in place. Also, I don't want a system that requires the driver to plug something in, wave the key fob around, and so on - to the outside world it should look as though the driver has just got in and started the car in the normal way.

The sort of thing I'm thinking about is a loop of wire round the passenger compartment (or just next to the driver) that either stimulates or responds to a passive transponder. For instance, the transponder could be a tuned circuit that affects the inductance of the sensor loop. Alternatively the loop could send out 'interrogation' signals, to which the transponder responds (but that implies a battery).

Once the ignition is on and the system's made its connection with the transponder then it will shut down until the ignition is turned off - the relays already installed will lock themselves until the ignition is turned off.

The output I require is a closed pair of relay contacts, from which I'll activate the relays that operate the 'security features' on my car. I'll happily build a bit of circuitry and program it, if that's required.

Any pointers, clues, or past experience greatly appreciated. If I get anything to work I'll make details available here.

cheers,
David

Sounds cool I'd be interested in this too!

Cheers

Mark

RFID would sound like an obvious contender, I'll have a bit of a look-see and get back to you with anything I find.

Nick

There's 2 types of RFID as far as I know. Short range and long range. Sort range is like you may use for building access at work, teardrop keys, card entry etc. You can get a hobby kit fairly cheap eg: -

http://cgi.ebay.co.uk/Electronic-door-lock-RFID-tag-reader-2-Tags-EM4102_W0QQitemZ7544055738QQcategoryZ4660QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

However this only works up to about 10cm away. However perhaps if the receiver was under the seat near the pocket you keep the fob in?

Otherwise there's long-range RFID kit. Costs more, and dno't have any links off hand. On the plus side they can work up to tens of metres away, on the down side they require a battery for the extra power and are therefore bigger.


But here's an idea. You can get rfid tags that are really tiny, so for example if you had the RFID receiver near a start push-button, then when you press the button it would start only if you have the tag near your hand - for example stuck to the back of your wristwatch.

Or do what this freak did and have one surgically implanted into your hand: -

http://www.flickr.com/photos/28129213@N00/sets/181299



[Edited on 7/9/05 by gingerprince]

sounds good...I'm all ears too...

That's a good-looking system, but it would be nicer if the range was around 1 metre or so. It certainly has a useable output for my needs.

Looks like RFID is the way to go - anyone got some more links?

cheers,
David

You can get mid range systems, such as this one (700mm - £190)

http://www.rfidshop.com/index.asp?function=DISPLAYPRODUCT&productid=39

or this one (450mm - £60)

http://www.rfidshop.com/index.asp?function=DISPLAYPRODUCT&productid=803

but as you can see the price jumps up relative to the range it works at.

If anyone can find a decent online supplier of RFID tags and readers, can you post the site on here for me?

Cheers,
Nick

[Edited on 7/9/05 by nicksertis]

One of the first smart cards (by GEC) broadcast an FM signal to the card. The card rectified that to provide micropower to the electronics. The card responded with an AM signal which it generated by shorting it's radio coil with a transistor. The transmitter would "feel" an AM pull on the power to its transmitter and could read the signal from that. This way you can have a batteryless transponder.

You don't want too big a radio range, if a thief is trying to seel your car, you don't want to re-mobilise it as you run towards it to stop the thief.

mmmmmmmmmmmmm a very interesting thread indeed I'm interested too.

Anyone with a Maplin catalogue handy? I did a quick search on their site to see if they have any RF kits, might be able to knock an RFID system up if I can get all the components. Would be interesting to see how cheap an entry level system could be setup for.

Ideally we'd end up with a set of plans to make one from scrach, in the true spirit of the locost.

Nick

I was thinking of using the HCS473 series from Microchip. They enable passive keyless entry and are code hopping so that the code constantly changes. I have a couple of the chips at home, i just havent got arround to playing with them yet, you know how it is, to many projects on the go!

Press Release

Microchip Site


Regards,
Scott.

[Edited on 7/9/05 by MonkeyHunter]

Well, that'll be some light reading for the train tonight!

I can see just one problem with that device - clicking on "buy/samples" it says that they're not available yet!

David

I use the Clifford virtual key on mine, transponder in my left trouser pocket and the pickup in the seat cushion. Jump in flip the aircraft style switch on and press the starter button. Amazes most people that i have no Key in a car with no roof.

quote:

---

Originally posted by MonkeyHunter
I was thinking of using the HCS473 series from Microchip. They enable passive keyless entry and are code hopping so that the code constantly changes. I have a couple of the chips at home, i just havent got arround to playing with them yet, you know how it is, to many projects on the go!




Regards,
Scott.

[Edited on 7/9/05 by MonkeyHunter]

---

quote:

---

I can see just one problem with that device - clicking on "buy/samples" it says that they're not available yet!

David

---

Maplin do a transponder key fob thingy:-

Link

But the range is only about 2 inches.

A mate of a mate has a Caterxxxx R500 which has a key fob style alarm, he fitted the reciever in the tunnel near the seat, so that when he sat down, with the transponder in his pocket it would start. Anyone else who sat in the seat and it wouldn't start.




At £3.99 its locost if nowt else.

Mike

errrm, try 3 - 6mm not 2 inch!!!!!

if it was 2inch i'd be impressed and get one for that price, for 3-6mm........ hmmmm

the german company who manufacture the item also do a version with slighly longer range, the B231, up to 15mm

http://www.kemo-electronic.com/en/bausaetze/b231/index.htm
now if we could get them to do one that had a range of 15 to 20cm's ...........