looking for a promity sensor/switch setup?

[paradoxblue]

I am trying to find something, i can either buy or build. That has a proximity sensor in it.

Meaning. I will carry something on my person [x]. and There will be a unit designed to trigger when it senses [x] is within so many feet.

I'm trying to build a push button start system for my car. That will only work if it senses my device is within the car,

so I sit in the car. The button illuminates to tell me it senses me. and then i can press the button and away I go.

On the same sense it would be sweet if when I walked away it would cut the sensor. etc

can anyone think of a system or circuit i can use to do this? i know how to do the push start etc. just wondering about a sensor circuit.

any input or help would be great.

thanks!

 

[Living Weapon]

For $49.95 Rat shack has an RFID reader: http://www.radioshack.com/product/index.jsp?productId=2906723

It comes with passive RFID tags so there's no batteries to run down in the thing you carry on your person. RFID is short range, so you won't have to worry about your car being started and stolen while you are sitting in your living room, or inside the corner store. The bad news: the interface looks like a 2400 baud modem, so you'll need a carputer or embedded controller (e.g. a basic stamp, etc) to tie it into your start switch - you could also automate locking the doors and rolling up the windows when you step out of range, and maybe flash the lights to give you positive confirmation that the car is "locked".

In general, anything that is secure will have a serial interface - most of these units tie into an alarm panel or timeclock system, for building access control or employee timecard systems, respectively. Simple systems that provide a logic signal you could tie directly to a relay are probably not secure enough for a car - I mean, you have security through obscurity because the average thief wouldn't guess what specific system you choose, but if you ever did have your car stolen the insurance company would probably nitpick the security of your system. Hence, cars that have factory options like Keyless Go (tm) use fairly involved encryption so that the same code is never passed twice between the keychain and car. RFID is a good compromise, because it is unlikely the casual thief or vandal can duplicate the ID - an RFID can be scanned and impersonated, but so far hardware capable of doing this isn't cheap.

 

[agent420]

I'm thinking RFID as well. Chip yourself

 

[paradoxblue]

yeah i was looking towards that also. but the fact of having the carputer and everything is something i don't like. plus the carputer would need to be started up at all times to be able to see me.. drain the battery.

need idea for home locks though

 

[Living Weapon]

a USB programmable Basic Stamp micro controller is the way to go - minuscule power draw, less than $40, and you don't really want a full-blown carputer and all the associated software between you and the start button - that's just too much that could go wrong and leave you stranded, or at leasts futzing around when you'd rather just go. A micro controller is simpler, since it is dedicated to just this task - less to go wrong ...though you'd probably be writing the code on it from scratch, but that'd be a great way to learn.

 

[tobiath]

Mitsubishi has this - they call it the FAST key system (you keep your keys in your pocket, bag, whatever), it senses when you're near so it can unlock the doors and unlocks the turn mechanism that replaces the key slot, so you can now turn the mechanism to start the car - its not true push-button, but that is what you are asking about, correct?

I know its packaged together with the GPS unit on the 2008 Lancer GTS (they attempted to sell that for an extra $2200 when I bought myself a new car. I didn't want the GPS and didn't want to spend such a stupid amount of money on that nice little utility), and I'm sure they're packaged similarly with their new cars.

Check around to see if there is any information on the FAST key system though, to see if anyone figured out how to make and rig up their own.

quick edit: the system functions with the ignition mechanism unlocking when key is in the car (left in your pocket) and locks when the key is not inside the car (you step out), and the door locks function similarly - when you get close, again with your keys in your pocket/bag/whatever, push a small button on the driver door handle (placed in a location where you would usually put your thumb when opening the car door) and the doors all unlock.