As I mentioned before I'd like to keep the stock tach if possible. Worse case scenario I replace it. Not a big deal, but not as fun either.
Speaking of fun, in order to simulate the new motor spinning and the new RPM sensor I decided to build a pulse generator. This pulse generator creates square wave pulses of different frequencies. These square wave pulses basically duplicate the output of the RPM sensor. By feeding pulses of a known frequency I can see if the engine control module(ECM) will properly drive the tach.
Now I could have easily purchased a pulse generator, but what fun would that be. Any excuse to sit by the fireplace on a cold day, look productive, and use a soldering iron shouldn't be passed up.
This is a picture of the circuit while I was playing with it.
Here it is mounted on a board. I'm showing you the nice side of the board. My soldering is not pretty!
And here is a picture of the oscilloscope tracing showing the square waves produced by the pulse generator. As an aside Ebay is your friend(...oscilloscope...$4 ebay :-))
Next step is to attach the generator to the ECM. The ECM expects a voltage of 5V. This only puts out 1V so I'll need to hook it up to a small amplifier for testing. Maybe I'll build the amp too! Oh wait, I already built one a few years ago for my son's guitar ....just for the hell of it :-)
3 comments:
Been sending out this info for all Saturn people trying to get the tach back! The square wave u have will not work on the position sensor but it might work on the whitewire to the tach below is why.....
I know the crankcase sensor sends out 6 pulses and a sync pulse that the DIM module converts to injector pulses AND tach pulses. Oh the ABS and cruise use the Vehicle Speed sensor on the transmission... but you probably know that. I have yet to find someone that has said or documented all the wire uses. I will keep u posted as I have others trying to find out tachometer pulses.. if every 4 pulses is one revolution then 4000 pulses equals 1000 rpm (4 x 1000) ... so a square wave 0 to 5 volt at a 66.66 cycle per SECOND - 50% duty cycle - square wave (4000 /60 sec) should equal 1000 rpm on tachometer.. too high then 33.33 cps would be two pulses per rev. maybe I can tell this way! Or maybe I am wrong lol.....
Dave
Dave,
Thanks for the info. See the next blog entry for the results.
Barry
I hope u try the White wire to the tach... take it off the DIM module and connect the 5 volt square wave to it... Be sure the power is on and that u have a common ground from the pulse gen.. people have said they get a + 12 to ground off the white wire from tach.. This - I think - is a pullup resistor in the tach! So let me know !
Dave...
grassrts@newnorth.net
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