Quick sanity check here - 2,3 set to On on the dip switch, pins 1+2 jumpered for square wave on primary tach, 2nd trigger jumped to I1A if following Braineack and diyauto's instructions? Anything else?

 

That sounds right.

If you followed Brainey / DIY's input mod instructions, then you have pullups on the MS board for both lines and will not need to jumper pullups on the stim. 2 & 3 on, all others off is correct for the DIPs, and you want a squarewave output on the primary.

 

Thanks, now I need to hunt down where I'm losing signal. Don't suppose you have a cheap suggestion for an oscilloscope?

 

Doing the best I can with an old multimeter - looks like I am getting secondary trigger all the way to pin11 on the CPU - at least its wiggling my needle in time. Whats the primary tach input pin for the CPU?

 

The primary input is pin 14 of the CPU, which is the hardware IRQ line. It senses falling edges (at the CPU).

Cheap is relative as far as O-scopes. For years, I was spoiled by having access to $5k Tek scopes at work that I could bring home on weekends. Currently, I have a USB scope, which was about $250. Basically This one. It can be slightly frustrating at times as a lot of the controls are different from a real scope, and a few features like one-shot trigger never seem to work right, but for the price it's fine.

If you want to go super-cheap, a few folks have home-brewed oscilloscope-like functionality with their sound cards. Google Sound Card Oscilloscope and you'll find hits like these:
Electronics: Soundcard-Oscilloscope
Oscilloscope for the Soundcard
Zelscope: Sound card oscilloscope and spectrum analyzer

You'll have to build some simple hardware for the inputs, and the speed of these is pretty pathetic compared to a proper scope (44ks/s gives you an effective 20Khz resolution, which is worse than my 30 year old analog scope) but most automotive sensors are very low-speed by comparison, so it'd probably work. I'll have to try one of these some time- it'd save a lot of hassle when people on m.net say "I'm measuring X with my voltmeter and I can't tell what's going on."

 

Sorry for my noobness but why do we jump 2nd trigger jumped to I1A?

 

Because that's the pin we typically wire internally to JS8.


The Miata's CAS has two outputs. The CKP output gives two pulses per crank rev, which are the primary triggers. The CMP output gives one pulse per crank rev, which is used by the CPU to figure out which CKP pulse corresponds to 1/4 TDC and which corresponds to 2/3 TDC.


The 2'nd trigger simulates CMP.