tacho/rev counter - solutions

[Vincent Waldon]

Hmmmm... then search has let you down... I remember posting oscilloscope pictures of both the gasser and W tach signals... lemme see....

Is this what you're after:

http://www.vwdiesel.net/forum/index.php?topic=13499.0

[rodpaslow]

I think I'm going to try going the way of the hall sensor.  I have some spare parts from a 90 dist. and I pulled the round window trigger from it and plan to put it onto the end of the cam bolt and set the sensor itself to word just like it did in the distributor.  It's going into a 96 and I'm hoping I can hook that directly to the tach....

[Vincent Waldon]

Cam rotates at 1/2 engine speed, and the gasser tach is expecting 2 pulses per rev, so you'll need 4  metal flags on your cam for an accurate tach measurement.

If I did the above math correctly...someone will jump in if not  

[Kudagra]

So here is my thought.

Ive mounted a Ford Taurus alternator..and I no longer have AC or PS. I have this spare pulley on the front of my crank. I want to use the 2 mount bolts, towards the firewall that the PS bracket used, to make a sensor mount that would read off my modified unused pulley. If I have to add something or remove it from the pulley I dont really care. What Im looking for is what will my sensor have to put out.

Ive debated tearing into a Ford Duraspark (Ive had alot more experience with the Fords) and taking the distributor pickup out and using that.

I just have NO faith in the W terminal...specially since I dont have one anymore. So..will I just need ANY kind of sine wave?

[Vincent Waldon]

So..will I just need ANY kind of sine wave?

Any documentation I've read indicates that the tachs are not very picky signal-wise... a good clean transition between 0 and something greater than 5V seems to do the trick... 2 pulses per rev... square/sine doesn't seem to matter.

Kinda makes sense... the ignition system is pretty noisy so a picky tach would be problematic.

[Smokey Eddy]

I was wondering if anyone knew of a source for just a normal photosensor that will count say a white dot painted on the crank pulley and output a signal that any standard tach could read?
like say an "aftermarket" tach?

the FAQ doesn't have anything on this and i can't seem to choose the right words for a search to bring up anything useful.

[Kudagra]

So..will I just need ANY kind of sine wave?

Any documentation I've read indicates that the tachs are not very picky signal-wise... a good clean transition between 0 and something greater than 5V seems to do the trick... 2 pulses per rev... square/sine doesn't seem to matter.

Kinda makes sense... the ignition system is pretty noisy so a picky tach would be problematic.

See..thats what I wanted to know. What kind of voltage peak do I need to create to get the tach to work.

[Vincent Waldon]

Just so long as you've noticed all the Vince weasel words: "kinda", "seems to", "should be"... 

I've fooled around with this stuff a bit but have never done the definitive test, which would be to use a bench signal generator to play with the tach's mind "mo ha ha ha ha... lets see how you like a triangle wave Mr Gasser Tach".  "Oh really... a ha.... yah... you like that, don't ya".   

[rodpaslow]

I noticed with reference to the link to the ocsilliscope, that optical and flywheel pickup are noted, but not a hall type setup.  I have a 90 Jetta 16V I converted to run on megasquirt.  The hall is easy to use a pullup to and it will send a clean (depending on size of resistor) 0 - 12v square signal.  I could not get this to work with the vw tach in the car.  I have an aftermarket autometer in it.  I don't want to have to spend big$$ to buy another autometer.

Is there a way to pullup the 12V to a higher voltage as per the link (80V on gasser tach) to get the hall to work nicely with a gasser tach.  As I expect the 96' tach will need something similar in order to work properly.  I'm a major novice when it comes to electronics.  (I tried Rogers optical unit, could not get it to work - I figure the hall unit will be easier to setup)

[Smokey Eddy]

I noticed with reference to the link to the ocsilliscope, that optical and flywheel pickup are noted, but not a hall type setup.  I have a 90 Jetta 16V I converted to run on megasquirt.  The hall is easy to use a pullup to and it will send a clean (depending on size of resistor) 0 - 12v square signal.  I could not get this to work with the vw tach in the car.  I have an aftermarket autometer in it.  I don't want to have to spend big$$ to buy another autometer.

Is there a way to pullup the 12V to a higher voltage as per the link (80V on gasser tach) to get the hall to work nicely with a gasser tach.  As I expect the 96' tach will need something similar in order to work properly.  I'm a major novice when it comes to electronics.  (I tried Rogers optical unit, could not get it to work - I figure the hall unit will be easier to setup)

yeah i was hoping for something a little easier/less work. like just a normal pickup off of basically any new tdi. I would imagine they would just use some type of photo sensor like that no?
I think i'll try Roger Brown's optical unit.

[truckinwagen]

since I am already knee deep into digital gauges, I am tempted to get the Auber tach and hall sender setup, and put four magnets on the cam pulley and call it good.

I agree that analog is better, but the tach would be more a tuning and setup tool for me than something that I look at all the time.

[Kudagra]

since I am already knee deep into digital gauges, I am tempted to get the Auber tach and hall sender setup, and put four magnets on the cam pulley and call it good.

I agree that analog is better, but the tach would be more a tuning and setup tool for me than something that I look at all the time.

I want to use an aftermarket tach. I really dont trust the VW ones...and I like a clock.

My goal is to eliminate as much VW electronics as possible. German wiring is only slightly better then English wiring.

[Smokey Eddy]

My understanding of Roger Brown's little write up there is that it would drive the feed wire of an after market tach...