Originally Posted by ericgibbs

hi,
Forget the 2nd circuit option, its not going to work as you expect.

The 1st circuit option looks Ok, but it needs some small changes/additions.

As you are inputting nominal +12v [15Vpk] square wave signals you cannot directly use standard TTL logic to select the signal destination.

Can you confirm that the incoming signal frequency is less 500HZ?

As the Hall effect device is designed for 15V operation and is capable of sinking upto 40mA why are you considering a opto-isolator?

What are driving with the ignition coil EHT output?

ok thanks yep the in put is less than 500hz.

am thinking of using farchild AND gates a well as inwerters
https://secure.vividcluster.crox.net...ded/ZC4081.pdf

was not thinking wen sagested opto curlers