Active RFID ideas needed.

[Imagewerx]

Actually I need to make a PKE (Passive Keyless Entry) alarm for my car.I've had 3 different cheap Chinese ones and none of them have worked for longer than about a month,so thought I'd have a go at making one instead.
The ones I had before had a range of about 2 metres,so as soon as get 2 metres or more away from the car,the alarm arms itself automatically without having to press any buttons.Then as I return to the car,it automatically disarms itself when get about 2 metres away.
The car already has a 2-1 upgrade alarm in it,meaning it needs a positive pulse on one wire to arm it and the same on another wire to disarm it (2-1 doesn't have it's own remote).

So I've been looking around and found this.....
**broken link removed**

This is almost perfect as it gives me a bit more range above 2 metres which I really need,but it has a slight problem that it has a minimum range of 1 metre.This is a problem because it means I could leave my keys in the car and it would lock them in if less than 1 metre from the aerial.

So I need an active RFID system with an arm/disarm range of 0-6 metres or a bit more and can pulse alternate wires +ve on arm and disarm.I know there's dedicated chips I can buy for this sort of thing,but unless there's no other choice I don't want to get that involved with designing something like this from scratch,so I'd much rather have a part ready made system. Arduino would be ok though as I'm starting to get the hang of them now and they're cheap enough.

It doesn't have to be normal RFID,Bluetooth or anything similar that has the range will be ok as long as it's going to be cheap (ish) and reliable.

For those who don't know about PKE. The base unit in the car transmits a very low power signal at 125 kHz which as soon as the remote fob gets within range of it makes it automatically transmit the disarm signal on UHF,then as soon as you walk away and it stops picking up the 125 kHz signal it transmits the arm signal on UHF.

 

[Imagewerx]

Evening bump.

 

[Imagewerx]

Anyone got any ideas about this please?

 

[dougy83]

Hi,

As you've mentioned, the keyfob contains a low power transmitter and the car contains the receiver. For the transmitter and receiver, you can use e.g. 433MHz units or 2.4GHz units:
**broken link removed**
**broken link removed**

The 2.4GHz units will use less power than the 433MHz units, meaning that your battery will last longer. They will be more difficult to use however.

You'll need to connect a microcontroller to each end to allow the devices to communicate. Program them so that the transmitter transmits some code every second or two, and the receiver receives it. If the code is being received, then open the lock; otherwise close the lock. Use some formula to modify the code on each transmission so that it's not too simple for someone to retransmit your code to gain access to your car.

 

[Imagewerx]

Ok thanks for that Dougy. A couple of problems is that a microcontroller and that module and it's battery would be way to be big for something that I can fit snugly into my pocket and forget about it.I will look into it how ever and should nothing else come up,I'll look further into your idea.

 

[dougy83]

You should be able to get it all to fit in a box the size of a commercial keyfob.

If the transmitter is a little bulky, you can have a look at micro-sized ones, e.g. https://au.element14.com/jsp/search/productdetail.jsp?id=1304025&Ntt=1304025 (it's 7.08 x 5.2 x 1.8 mm in size)

 

[Imagewerx]

Ok thanks for that,but I've had another idea.
I've still got all three of the crappy Chinese ones I bought like this......
https://www.aliexpress.com/item/China-post-Free-shipping-Keyless-Entry-Alarm-System-Smart-Key-with-3-antenna-to-detect-driver/372625331.html
I know that the remotes still work on 433.92 Mhz and possibly even the LF transmitters on 134 Khz (I haven't tested the LF yet).If I canibalise the alarm module for the receiver board,can I use this to feed an Arduino to decode the data to a simple arm/disarm signal?