The simplest 'coded' key to replace a barrel lock on an old car (points, dissy, carb, etc) would be to have a 'pulse generator' in the 'key' - that would sync. with similar cct in the engine compartment (I see a lock-box containing the coil +electronic lock - to stop easy overriding).

What would be the simplest cct to build this type of lock?
Is there an even more simple way to replace a key electronically?

Thanks!

 

How about RFID tags

 

How about RFID tags

Sounds more expensive (as well as higher tech) than I need. But thanks!

 

What's wrong with just replacing the old barrel lock? Unless you find something that was designed as a drop in replacement you're probably going to need to learn a fair amount of electronics knowledge including microcontrollers and their programming. iButtons are popular key / lock systems.

 

What's wrong with just replacing the old barrel lock? Unless you find something that was designed as a drop in replacement you're probably going to need to learn a fair amount of electronics knowledge including microcontrollers and their programming. iButtons are popular key / lock systems.

Thanks - I've got a fair idea about electronics, but it's mostly academic knowledge - that is, I know enough through college to realise my limits.

However, I think the confusion here is down to explaining just how simple I would like this! I don;t care about an unbeatable system - I just want something more than a bundle of wires under the dash that a perp' can rip out and short the right ones together.

Here's what I've got so far:
So say I have a 'memory-stick-sized' square-wave generator (battery powered, using 555 say). I can drop it in my pocket/attach to house keys - then on getting into the car there is a socket that the dash.
Under the bonnet (hood) there is a device that switches on a live to the coil so long as (roughly) the right square-waveform is seen at the connector on the dash.

NB. It doesn't have to be a sq-wave (a timed spike will do if simpler). The connection would be via a twisted pair to minimise interference to radios, etc.

A barrel lock/key would probably cost about the same, but this would be something a bit different and also being a one-of-a-kind would stump a potential thief much more than a lock.

 

However, I think the confusion here is down to explaining just how simple I would like this! I don;t care about an unbeatable system - I just want something more than a bundle of wires under the dash that a perp' can rip out and short the right ones together.

The old hidden switch is a much better way for an old style ignition system. I know it's not a high-tech electronic gizmo but guys have been using them for years.
http://www.streetrodderweb.com/tech/0602sr_alarm_systems/index.html

 

A barrel lock/key would probably cost about the same, but this would be something a bit different and also being a one-of-a-kind would stump a potential thief much more than a lock.

I didn't realise this would be such a difficult concept to get over!
Sure a barrel lock is simpler (& no more expensive). ... Sure a hidden switch is an easy solution (though easily beatable if the guy can get the bonnet open).

If I can explain (again) - can I just have ideas (or even pointers as to where I should start thinking for myself!) as to a fun simple cct that can act as a basic electronic 'lock'!

Okay - attempting to engage brain-cells (if you only want to respond to say why my idea is unworkable/stupid please do!)...
> A tuned RC oscillator in the 'key' - when plugged in 'latches' an Op-amp with the right feedback ... that runs logic stage (or a Zener?) to get a level - holding a solenoid On.

 

I had a very simple method, using virtually no complex components at all. Take apart a USB stick, and solder two loop lines onto either pin combination you wish, remove the board contacts. Then purchase a female USB and wire it into the control side of two relays. One relay for the ignition system, the other relay for the fuel pump. Make the control side of the ignition relay negative, and control side of fuel pump positive, or vise versa. Then place a 2amp fuse on the 12v supply. When wiring make all wires black, use clear shrink wrap to hold a "tag" with a number on it. Keep a wiring schematic handy so you can work on the car without being confused. Any combination of the 4 pins could be used, and even if a thief tried to just shove a screw driver in the socket, it instantly would short out and pop the 2 amp fuse. Or if they rip out the socket they would have no idea which of the 4 wires to put together. Virtually impossible to activate without your special USB plug in. Think I will make one for my racecar actually I made a crappy diagram to explain- ( yes I realize the symbols for ground are not correct, but you get the idea. lol)

 

If you want to detect a freequency you will need either:-
filters ... lo pas, hi pas, notch etc.
OR
PLL ... Phase Locked Loop circuit.
OR
Counters and a time period.
Honestly There are loads of ways.

Have you considdered an analouge system.
plug in the right rsistance, all you would need then is weatstone bridge ... ballanced and you enable the ignition, anything else your immobilised.
Something simmilar with a current loop would be better.

Just a acutionarry note .... BE VERY SURE you dont build something that might fail whilst driving it could kill you and other folk.

Al

 

If you want to detect a freequency you will need either:-
filters ... lo pas, hi pas, notch etc.
OR
PLL ... Phase Locked Loop circuit.
OR
Counters and a time period.
Honestly There are loads of ways.

Have you considdered an analouge system.
plug in the right rsistance, all you would need then is weatstone bridge ... ballanced and you enable the ignition, anything else your immobilised.
Something simmilar with a current loop would be better.

Just a acutionarry note .... BE VERY SURE you dont build something that might fail whilst driving it could kill you and other folk.

Al

Hi - Thanks for all your suggestions - sorry I hadn;t replied sooner.
I like the simplicity of the wheatstone bridge idea, etc. - I do take on your point about having a system that could 'cancel' the ignition whilst driving, and how dangerous it might be. - The fact that a wheatstone bridge can measure very tight tolerances might mean it is too risky for this use, as tolerances can drift.

How about a RC network (in the key) that can discharge via a Schmitt trigger (an Op-amp cct - locked in a box with the ignition coil)?

 

If your going down that route, or anything simmilar for that matter you could always employ an on and off button operating a latching relay.
Enable or disable the ON function with your 'key' but keep the actual ignition state latched with the relay.
No danger of anything sensative turning the ignition off unexpectedly

Also if you go with a bridge of any sort, use a window comparitor to do the sensing that way you can effectivly set a tollerance.
A couple of opamps a power transistor and a relay would do the job.


Al

 

If your going down that route, or anything simmilar for that matter you could always employ an on and off button operating a latching relay.
Enable or disable the ON function with your 'key' but keep the actual ignition state latched with the relay.
No danger of anything sensative turning the ignition off unexpectedly

Also if you go with a bridge of any sort, use a window comparitor to do the sensing that way you can effectivly set a tollerance.
A couple of opamps a power transistor and a relay would do the job.


Al

Some latching relays can change state as a result of mechanical shock or vibration. It would be unfortunate if the ignition died because of a bump on the road!

 

I totally agree but they also come with mechanical data that would specify their shock resilliance.
(Good call though I stand corrected.)

I meant, and should probably have said, 'latched' relay implying a none latching relay that is being held in by one of its own contacts, which is far less likely to bounce under shock conditions.

That said, nothing is safer than the origional ignition switch and any mod, as I said earlier, would need to be carfully considdered with resprct to relyability and therfore safety.

Properly done this would be no more danderious than a home installed car alarm with an immobiliser circuit.

Al

 

From the link above, This was mentioned, seems to be a professionally packaged version of exactly what you want.