Semi necrobump, I'm having tons of trouble with timing error in my ms2 install in my crx due to noise in the MS vr circuit. I can trim almost all of it out with the pots while its running but in doing so I can no longer start the car because it gets no signal at all when cranking. I've tried messing with the noise filter software stuff, but thats sort of a bandaid, is VERY poorly documented, and just isn't working. So as it stands I geet timing error of like -12 to +12, sometimes worse, and it causes me to have a poorly oscillating idle and bad recovery. It also makes starting the car a huge PITA. I'm just using the 4 tooth trigger on the stock dizzy in simple trigger mode (or wtfever its called).

To the point. I've ordered one of these chips from Digikey and the adapter board from protoadvangate. I'm going to solder it up once it gets here and build it out on some spare protoboard I have using the typical installation diagram from the datasheet. Am I correct in my assumption that I can just wire it directly into IRQ-1 on the MS, completely bypassing the built in circuit? Do I need to do anything to cut out the original other than just take out the jumper completely?

 

If you wish to place the circuit inside the MS enclosure, then yeah just remove the jumpers from both TachSelect-VrIn and VrOut-Tsel. Run a wire from TechSelect to the input of the 9924 circuit, and from the output of the 9924 circuit to the Tsel pad (which goes to IRQ-1). You will be totally abandoning the MS's internal VR/opto circuitry.


As you can see, the 9924's output goes low on positive zero-crossings of the + input, so wire your VR sensor to it accordingly. Polarity matters.

 

Cool, thanks for confirming my assumptions. Hopefully it will resolve all my issues.

If I have polarity backwards, can I not just change that in MS? Isn't that what one of the trigger settings is?

 

props to kday for the schematic and board layout files.



One question: I know this pcb has a 5V pullup, but do I need a pullup BEFORE this circuit? ie do I need to hang the raw 2001 CKP signal to 5V via a 3.3k resistor and then run it into IN+?

(same for CMP)

Voltmeter shows .800ish volts max on the output of the sensor.

incidentally, depending on which way I wave MY screwdriver, the output either hangs high or low and the pulse is the opposite direction. ie if the engine rotates the other direction, the signal is inverted.

 

You don't want a pullup on the sensor side. It generates its own voltage.

If you spin something past it close and fast enough you'll see a lot more than 800mV. I blew the 63 volt rated input stage on one of my oscilloscopes spinning my trigger wheel. There is a diode clamp in the maxim part (unlike my oscilloscope) so with the series resistors it's not an issue there.

 

OK I will run the sensor straight to the 9926, power, and ground as appropriate.

I suppose it doesn't make a whole lot of difference what the voltage swing is since the 9926 has an automatic threshold, right?

 

Whatever the voltage is it'll be clamped to 5 volts in the 9926. The large swing signals are the easy part and any old VR conditioner will deal with those; the 9926 really excels at picking out the low amplitude signal. I was seeing good edges at like 200mV peak to peak.