Video explains it all. This is *not* an instructional video of how to connect, but instead is a simple first test and demonstration of my idea to use this circuit as an ignition and starter immobilizer for my soon to be plated 2006 KTM 525 dual-sport motorcycle.
This is NOT my own circuit design; I found a simple diagram and modified it to suit my application. I just searched google for ‘latching relay circuit’ and found this little drawing someone came up with:
http://www.instructables.com/id/DIY-Latching-Relay-System/
Here’s my what/when/why I’m doing this, in a bit more detail than I described in the video.
The concept is that I arrive at my machine and flip on the ignition switch, and get nothing– not until I swipe my RFID module (red status LED) and the latching relay circuit will keep the circuit alive (green status LED) until I turn off my existing ignition switch on the handlebar. The whole RFID system will be completely dead, along with the rest of the bike, until the ignition switch is on. This system shouldn’t represent any leeching battery drain.
I think I will use some very strong velcro so I can attach the keyfob into place on the bike somewhere near the RFID transceiver, which will effectively defeat the immobilizer system and make it start just with only the ignition switch. I’d also attach the keyfob to a lanyard or carabiner that is attached to the bike so I don’t accidentally lose my keyfob. At least I have two, and the ability to program more 
In addition to this security measure, I’ll probably get myself a disc-brake lock w/ cable lanyard.
I’ve added a third relay because the +12v output from the RFID system was not capable of driving two relay coils; Only one. So you only need two SPST (or SPDT) for the latching relay mechanism. In my case there are three, but the first one might as well be assumed as part of the immobilizer circuit, and only drives the other two relays.
I might use a SPDT + DPDT relay so i can handle both my ignition and starter kill with one physical relay, and further minimize the number and size of components necessary.
- Post Time: 04-30-16 - By: http://www.rfidang.com