scudderfish
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 posted on 11/3/11 at 07:42 PM |
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Circuit design query
A while back I bought an RFID reader from ebay, and I want to wire it into my ignition circuit. My goal is to place the reader under the drivers seat
so it detects the fob in my pocket. On the dash I then have a toggle switch and a start button and no ignition key. The way I see it is :-
Toggle switch is input A. If this isn't switched, nothing happens. RFID reader is input B. If A and B are live then a relay controlling the
ECU feed is live and I can start the car. If B goes away, then the relay is still energised. I don't want the engine to die if the RFID reader
loses track of the fob. When I switch off A, the engine stops and the car is inert. I did roughly sketch something out with two relays and a diode,
but I was wondering if anyone had any better/cleaner ideas on how to wire it all up.
Regards,
Dave
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HowardB
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| posted on 11/3/11 at 08:29 PM |
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is it possile to rip something out of a scrap car, mercs, nissans, renaults there are lots of models with something like this already.
might save building,....
Howard
Fisher Fury was 2000 Zetec - now a 1600 (it Lives again  and goes zoom)
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Miks15
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| posted on 11/3/11 at 08:36 PM |
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Why not just have the rfid in the starting circuit and not in the ignition circuit, then have the switch in the ignition circuit, the it can only be
started with both, but if the rfid loses connection it won't kill the ignition
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rallyingden
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| posted on 11/3/11 at 08:37 PM |
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Try This
RD
 
ecu relay small
[Edited on 11/3/11 by rallyingden]
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rallyingden
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| posted on 11/3/11 at 08:41 PM |
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By the way Dave Do you have a link to ebay supplier of rfid reader
Cheers
RD
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scudderfish
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| posted on 11/3/11 at 08:54 PM |
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quote:
Originally posted by rallyingden
By the way Dave Do you have a link to ebay supplier of rfid reader
Cheers
RD
It was kicked off by this thread http://www.locostbuilders.co.uk/viewthread.php?tid=131819
Thanks for the suggestions. I slapped my forehead on the obviousness of putting it in the starter circuit
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rallyingden
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| posted on 11/3/11 at 09:01 PM |
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Yes but I would not want anyone to be able to turn ignition on and "play" or even bump start my car
RD
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HowardB
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| posted on 11/3/11 at 09:13 PM |
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put the switch back into the ignition crcuit, and make the relay that it controls into a latch, ie it all stays on till you switch it off. once off it
needs both the switch and the rfid to cause it to latch again.
prob easier to draw than describe, I'll go and look for paper
Howard
Fisher Fury was 2000 Zetec - now a 1600 (it Lives again and goes zoom)
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ChrisW
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| posted on 12/3/11 at 12:05 AM |
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I'd use a thyristor on the ignition relay circuit. It will work like a latch, so when you turn the key it will switch the relay on as soon as
it sees an input from the RFID. Once on it won't disable until you turn the key off.
This kind of circuit is used in electronic kits for the 'steady hand game' you buy from Maplin and the like to make sure the buzzer stays
on even if you only touch for a fraction of a second.
Chris
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Miks15
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| posted on 12/3/11 at 02:26 AM |
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ahh yeh didnt think of the being able to turn everything else on! my bad,
Go with one of the other suggestions
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scudderfish
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 posted on 12/3/11 at 01:36 PM |
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Oooo, I'd not heard of thyristors before. They look to be exactly what I'm after
Regards,
Dave
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trextr7monkey
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| posted on 12/3/11 at 03:20 PM |
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We buy thryistors for afore mentioned latch circuit in steady hand game for kids from Rapid in bulk, if you need any for expeiriments get in touch so
you don' pay over odds for postingatb
Mike
http://www.flickr.com/photos/14016102@N00/ (cut and paste this dodgey link)
Our most recent pics are here:
http://s129.photobucket.com/albums/p211/trextr7monkey/
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MikeRJ
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| posted on 14/3/11 at 10:22 AM |
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You probably don't want to use an SCR (the type of thyristor you are probably looking at) unless you fully understand all aspects of the devices
operation. It will drop considerably more voltage than a relay for starters, and the device can be triggered (and possibly even turned off) by
voltage spikes across the cathode and anode. Not a problem for a "steady hand game", but most certainly something you need to account for
if designing it into an automotive system.
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scudderfish
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| posted on 14/3/11 at 10:45 AM |
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My intent is that it only switches a relay which handles all the 'real' switching, so voltage drop should not be a problem. I guess some
sort of capacitor should be included to smooth spikiness. Nothing like a bit of added complication to make it more fun
Regards,
Dave
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Brooky
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| posted on 14/3/11 at 06:48 PM |
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I used one of these on the last car, and will use it on the next one too.
They are great.
Toad Sterling Excel Thatcham Cat 2 Immobiliser Warranty on eBay (end time 05-Apr-11 18:47:38 BST)
I just kept the keys in my left pocket, sensor on the tunnel. When I got in the drivers seat, the ign and starter circuits came live.
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scudderfish
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| posted on 12/5/11 at 02:17 PM |
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Well, it sort of works
On the bench it switches the relay on and keeps it on when I wave the rfid token near the reader. However, when I plug it all into my car it craps
out, normally within a second or so. I'm guessing that the fuel pump and others are causing electrical noise that is freaking out the
RFID/thyristor circuitry. How should I go about fixing this in as locost a way as possible? Can I get away with just whacking a capacitor between
the +12v and ground? If so, what sort of value would be a starting point? If not, what should I do? My backup plan is to buy a laptop adapter for
an Asus Eee (as they supply 12v 3A) and cutting the plug off as that should contain a full set of smoothing and regulating.
Regards,
Dave
[Edited on 12/5/11 by scudderfish]
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