Magnetic trigger sine wave reduce noise or digital conversion

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frankr2994

Joined Apr 30, 2020
1
Hi I'm at the end of the ropes here. I am not an engineer I am a race car mechanic. I am currently trying to get a stand alone fuel ignition system working on a customers 79 Bentley. The ECU needs a rpm trigger it can use either a mag trigger or Hal effect. I didn't really have an option for either but I was able to retrofit the distributor with a mag trigger. Issue is I can't get a clean enough trigger above 2500 rpm. The ECU takes the sine wave input and converts it to a digital square wave and doesn't have many options as far as adjustment. I can set a low or high filter and a minimum voltage. Low filter create erratic issues at even idle. Setting minimum voltage above .45 does not allow the vehicle to start. I have tried new pickups new wiring twisted the wiring and shielded it along with disconnecting various electronic components that may be changing my trigger. I really need a way to either clean up my signal or convert it first to a clean digital signal. I know both can be done but it is very much out of my scope of knowledge. I'd greatly appreciate any help.
 

geekoftheweek

Joined Oct 6, 2013
347
You could try at MAX9924 to convert your magnetic to square wave https://datasheets.maximintegrated.com/en/ds/MAX9924-MAX9927.pdf. It is a rather small IC though and can be a pain by itself. There is also http://www.jbperf.com/dual_VR/v2_1.html that is based on the IC, but with that cost may be an issue. The 9926 version is a little easier as it doesn't have some of the extra components to add in to the circuit. I can't recall the exact part number off hand, but the original GM HEI module used an IC that can be picked up for a couple dollars too to convert the magnetic to square wave.

Other than that keep looking at ground wires. I've kind of been down this road with a home made controller that I could never get right due to various interference and since the vehicle has seen it's better days I finally gave up.

Another place to check is the megasquirt site. They have had a couple different triggering circuits over the course of it's life and the schematics are all on the site.

I'm thinking maybe if you convert it to square wave before the ECU it may help although I could be wrong. It may be your pickup is producing a wave form that isn't what the ECU was designed to see. Although they may look the same and supposed to work the same not all pickups produce the same shape of waveform. I found this while playing with some GM and Ford distributors to make my idea work.
 
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