Tom M'Guinn

I though I had a square tach laying around to test but couldn't find it. I suspect the tach is looking for a square 12v cycle, the frequency of which increases with rpms. Again, guessing, but imagine it triggers on the rising or falling edge...

Tom M'Guinn

I put my little pc scope on the tach signal and confirmed it gets a pulsed signal. If you follow the schematics, this is clear since the tach is fed the same ignition signal as the KLR straight from pin 21 of the DME. This is the same pin you tap to get rpm's on the zeitronix, etc. The 28.1Hz and 35.6ms shown in the screenshot passes the sniff test as well, since that is what you would expect at an idle of 840rpm's. By the numbers:

840 rpm is (840/60) 14 revolutions per second. At 2 ignition events per revolution, you would expect to see (14*2) 28 pulses per second -- i.e., 28Hz. If you divide 1 second into 28 pieces, you get 1/28 or about .0356, which is 35.6 thousands of a second or 35.6ms.

So, create this pulse however convenient, and you should see 840 on the tach.

F18Rep

Tom... quick side note question, can you say more about this app, I'm way over due for an upgrade (from my 1960 Heathkit)...Bruce

Teddy952

Great information Tom. Do you have a link to that app?

Tom M'Guinn

It's not just software, it is a simple/learner's USB o-scope from parallax. I'm sure you can get more hardware for less but parallax has really good educational documentation I haven't found elsewhere...

http://www.parallax.com/Store/Microc...me,ProductName

nofalls

Tom,
good stuff. I can make the jimstim generate that pattern and duty cycle pretty easily.

nofalls

Sorry for the lag on this. My son has been sick and my wife seems to think I should spend more time in the house right now. I'll drag the jimstim to work this week and see if I can set it up over a lunch in one of the labs.

Lumbergs Lackey....MmmmKay

Hey guys is it possible to get the pin out for the 986/987/997 clusters? I'm building a Porsche simulator and need the pin out. Any help is appreciated.

Tom M'Guinn

That question probably will get more response in the rennlist section(s) for those cars. I only have schematics for the 944 series...

Lumbergs Lackey....MmmmKay

I'd take those as i also have those gauges

I'd greatly appreciate it if you could.

Thanks

Tom M'Guinn

Well, I confirmed your connections and applied a square pulse from an Arduino (I just used the example "sketch" called "blink" and changed the speed to get a good reading on the tach). Worked like a charm. I also checked with a lower tech approach by applying 12 volts and ground to those terminals, then tapping the signal terminal with a wire attached to ground. The tach is driven by ground pulses, not voltage, so rapidly tapping the the signal terminal to ground does the trick. It doesn't make a nice clean rpm on the tach like in the video, but you can get it to jump around that way.

Teddy952

Thats perfect! So I should be able to get the tach to move by the following...
+12v -- term4
ground -- term2
tapping ground -- term3

Ill give it a shot today and let you know. Fantastic work Tom... thanks!

gregeast

While you guys are in there futzting around can you please sort out why our fuel gauges only ever manage to read Full about as often as the Cubs win the World Series?

Teddy952

I connected my +12v DC source to the A, B and C connectors in pic...
By tapping the wire connected to A to ground the tach moves.
Very easy test to do. Thanks again Tom.

Greg -- You sure its not full due to the price of gas? =) I believe that when the gauge sporadically shows full its a fuel sender issue. Not sure though.

gregeast

You may be onto something with the price of gas. I have pulled the sender, done the diagnostics and it appears to be functioning properly. I 'may' have even replaced it, it's been awhile. Regardless, it generally reads 3/4 when I fill up, although it will on occasion read 4/4 (or close to it). Not an uncommon problem from what I read. Seems like the sweep of the gauge just doesn't coincide with the signal it receives from the sender.

Sorry to derail your thread, but I would love to figure this out.