First Post - Circuit Design Need Help

[douglee25]

It's not always advisable to cut off the ignition like this and then start it again. The cylinders are still taking in a fuel/air charge and pumping it out the exhaust. It can potentially backfire.

You are correct, this could potentially happen. The engine is carbureted and running off two little primaries at idle. The idle is set around 650 rpm's. The throttle is never advanced during the ignition cut off. All these items combined make the possibility of a backfire very small. Also, the cirucuit that I'm constructed is basically identical to what the factory had installed. The factory unit however is pricey and if I can make the circuit for $10 bucks and learn something in the process, why not?

Doug

 

[douglee25]

Philba,

Concerning your schematic, I'm still pondering where the switch is wired to? What about the other 12V source points (Pin 4 and Pin 7)? Are they all wired into the switch as well or are they constantly receiving 12V and Pin 8 is the only pin that is switched for the 555 timer?

Doug

 

[philba]

all the double arrows with +12V are wired together - there are 4 of them. it's a way to avoid having a gazillion lines all over the place. just like ground (there are 4 ground connections, too). so, the switch turns on power to the entire circuit.

note, pin 7 doesn't connect to +12V, it goes through the resistors/trimmers.

by the when you get it all wired together, set the two trimmers at about the half-way point. that should be pretty close to a reasonable pulse rate and duration.

 

[douglee25]

all the double arrows with +12V are wired together - there are 4 of them. it's a way to avoid having a gazillion lines all over the place. just like ground (there are 4 ground connections, too). so, the switch turns on power to the entire circuit.

note, pin 7 doesn't connect to +12V, it goes through the resistors/trimmers.

by the when you get it all wired together, set the two trimmers at about the half-way point. that should be pretty close to a reasonable pulse rate and duration.

Thanks for all your help. I'm going to give this a go soon. Thanks again.

Doug