kill switch

[darinsquared]

I have a gasoline engine pump with a 12V electric kill switch.  I want to integrate a float with a proximity sensor that will shut off the engine when the tank is full.  Would this attached circuit work?  Would I be better off having the proximity sensor its own battery operated system?  Do I need t add a diode to prevent flyback when the engine shuts off?

Just a  note I put the zener diode in line as a switch so the current does not flow until the sensor reaches peak voltage.

Sort of on topic, what is a good circuit "checking" app for Android?

[darinsquared]

my apologies for some reason Paint will not let me save the image larger.

[Wimberleytech]

my apologies for some reason Paint will not let me save the image larger.

I dont have an answer but I fixed your figure.

[darinsquared]

thanks

[Delta]

Use a relay.  Assuming this is a magneto ignition engine, you get a surprising amount of current when you shunt the kill wire to ground.

A relay by it's very nature will snap fully closed when sufficient current flows through its coil, avoiding the grey area of your transistors linear region.

[darinsquared]

so would this work?  instead of using power from the engine for the proximity sensor I would just use a battery for the whole proximity switch/transistor circuit to control the kill switch circuit via relay.

How do I enlarge my image?

[Wimberleytech]

How do I enlarge my image?

If you are in windows7, while the image is enlarged on your screen, use the snippit tool (or Greenshot) and capture that to a file. 

If you are using Paint, open the file dialog box, go down to Properties,  change the width and height according to the size of the image you have drawn.