Read a capacitive signal and output a square wave

[drivefast]

I am working on an engine that needs a cam sensor. I’d like to just use the signal from spark plug one instead of drilling adding a cam sensor.

I know I can generate a current signal by placing a strip of wire over the spark plug wire but I’m not sure how to convert it to a square wave 0-5V. I was thinking about using a PnP transistor to control 5 volts. When the emitter has current the transistor passes the 5 volts.

Is there any thing I’m missing? Do I need to add any signal filters for cdi? Will waste spark present a problem?

 

[itsmoked]

How does cam position get controlled by spark? Spark is often retarded or advanced over the cam position.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[drivefast]

The aftermarket ECU I want to use is not picky when it comes to cam signal. It simply alerts the ecu to where in the fining order is cylinder 1. Once this is established the ecu can sequential inject fuel at the correct firing order.

 

[LateApexEE]

So how will the spark signal indicate when #1 is on the compression stroke? I suppose a distributor based ignition scheme could do this. But why not just use a cam lobe or spoke of the cam gear as a cam trigger?

 

[IRstuff]

I'm confused by what you say you want. Why wouldn't a simple comparator work? That's precisely their intended function.

TTFN

FAQ731-376

 

[TurboXS]

A common circuit in the past was to monitor the spark plug to trigger a timing light. Here is a google search for these;

http://www.google.com.au/search?q=e...7GGLL_en&redir_esc=&ei=ohSLS53cN4vY7AO5vby0DQ

Waste spark will give you a problem as these circuit aren't designed to discriminate between the "real" spark and the "waste" spark.

 

[waross]

Take the valve covers off and look for a lifter that is moving as #1 cylinder reaches top dead center. Put a sensor on that. you can mount it in the valve cover and kludgy as it may be, it will probably be a lot more accurate than a spark signal. And if the ECU is using the cam sensor to time the injection pulses it has a faint chance of working. That is more chance than a spark generated signal may have with many ECUs.

Bill
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"Why not the best?"
Jimmy Carter