Electronics > Projects, Designs, and Technical Stuff
Sensing an RFID car key?
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Psi:

--- Quote from: iXod on August 31, 2019, 05:47:06 am ---The rfid antenna is a ring around the key hole in the ignition switch. All that’s there is the antenna. The car’s ECU generates the RF signal and transmits & receives key IDs.

Your solution would require the antenna and an ECU. Looking at the car’s wiring diagram, there’s no “valid key” output. With a valid key the fuel pump runs and the ignition coils work.

--- End quote ---

I doubt the ECU is generating RF and sending it to keyswitch module. Since that would need shielded RF cable running ECU to Keyswitch module.
It must be a digital link to ECU So keyswitch module will have some smarts to talk RF to key.
Keyswitch module will talk over RF to the key and the ECU will talk digitally to the Keyswitch module.

So it's possible that even without an ECU connected the keyswitch module may poll for a key, even if it doesn't know what to do with it.
But yeah, im just guessing.
Yansi:
All the electronics of the RFID reader is near the keyway. No coaxial cables.

Not sure what would you need all those bulky measurement instruments for. Build a damn GDO! It is just a couple of trannies and a analog needle meter.

https://www.google.com/search?q=grid+dip+oscillator&client=firefox-b-d&channel=trow&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjR_uS8yazkAhVHLFAKHfdMCTQQ_AUIESgB&biw=1442&bih=775
Psi:

--- Quote from: Yansi on August 31, 2019, 07:22:35 am ---Build a damn GDO!

--- End quote ---

It's a car, not a Stargate.

 :-DD

Yeah, i know what you mean.


mikeselectricstuff:

--- Quote from: iXod on August 31, 2019, 04:01:15 am ---This needs to be portable and the smallest scope I have is a Tek 2465 series. Can an analog meter be used to watch for dip?

Something like: a sweeping (100k-150k ?) signal source driving a coil antenna, with an analog meter movement across the antenna (with rectifier and suitable multiplier resister in series with the movement)?

I have an Agilent 33120A arb gen that has a HV output. Specs say 10v p-p into 50 ohms; 20v p-p open-circuit.

Please help me by recommending a better circuit.

Thanks.

--- End quote ---
You could probably do it using audio - the ear is very good at hearing patterns and changes - I'd suggest something like sweeping the carrier with maybe a 1khz sinewave, and feeding the detector to an audio amp and headphones. Use the key you have to optimise the sweep range and audio sensitivity. It may also be possible to just switch between 2 frequencies instead of sweeping.
mikeselectricstuff:

--- Quote from: Psi on August 31, 2019, 05:51:19 am ---
I doubt the ECU is generating RF and sending it to keyswitch module. Since that would need shielded RF cable running ECU to Keyswitch module.


--- End quote ---
It's only 125KHz, barely RF. I've definitely seen schematics showing only the coil in the key/button assembly, don't know if they used shielded cable or not. Bear in mind these are only polled at startup, so it won't have noise from engine or other systems to contend with.
 
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