Engine start/stop help

[veltboy618]

Hey guys. I'm new to the site. I haven't been to school for electronics but I have repaired a few things in the past & I'm always wiring stuff up lol. I'm in the process of making a push button start kit for my older car so I don't have to use any keys to start it like the newer cars. I want to car to be a little secure so I'll be using a hidden RFID transponder so without the key fob my car will not start.

I have a NO momentary "engine start" switch,

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& I have a RFID transponder with 2 key fobs
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When the key fob is brought within 3 inches of the antenna on the RFID brain, the unique date encoded in the key fob is transferred to the sensor-receiver, activating the device-relay & the relay will turn on my ACC, & ignition. I will keep the fob my back pocket & the antenna will be fished up into my seat so when I sit down the brain will be able to read the code of the fob.

The engine start button will be wired to receive power once I press the brake pedal. When I press the "engine start" switch & close the circuit it will send power through a relay (getting power directly from the battery) then to the starter to engage it.


Once I press the button to engage the starter the car will start but here is where I confused. When I press the button to start the car I need the starter to stay engaged until I release the button (older cars take a little longer to start sometimes) then I want the same button to shut the engine off when pressed again instead of engaging the starter and making it grind against my flywheel. I was reading in a another thread and someone mentioned a D flip-flop. I looked into it a little & it seem like it can work for what I'm trying to do here. What do you guys think? Could someone help me draw this out so i can be wired up if it's even possible. Any input is appreciated!

Darius

 

[crutschow]

I believe you need more than a flip-flop. You want to be able to start the engine again if it accidentally stalls so I would think you need a circuit to detect if the engine is running, perhaps from a tach signal. You would use that signal to block the starter relay from engaging.

 

[shokjok]

What is the fob range? From my experience, if the fob battery weakens below the threshold voltage, you won't get an unlock or engine start condition. Will the engine stop if the fob is away from the ignition?