tacho/rev counter - solutions

[SteveH]

How about this ?
http://www.logjamelectronics.com/crimdts2.html

-Steve

[fatmobile]

I've been thinking of different ways to get a gas tach to work on a diesel.
Even went so far as to pull a tach apart and draw a schematic of the circuit.
 The gas and diesel were basically the same. Gas tach out of a '91 and a diesel tach out of an '85 turbo diesel Jetta. I figured I could probably swap a few resistors and caps and get the gas one to work with the diesel w terminal.
 This thread has been very informative. 2 pulses per revolution for the gas tach. I've also concidered using a sensor in the trany timing plug ... was thinking an optical sensor but with 2 pulses I could use a hall effect sensor (doesn't have to be kept as clean as the optical sensor) and have it trigger on the 2 raised metal pieces each side of the timing mark.
 I also want to figure out how many volts it takes to make the tack go to 7 grand. Maybe bypass all the circuitry and use a digital to analog converter ... turns number of pulses into a voltage value.

[SteveH]

This thread has been very informative. 2 pulses per revolution for the gas tach. I've also concidered using a sensor in the trany timing plug ... was thinking an optical sensor but with 2 pulses I could use a hall effect sensor (doesn't have to be kept as clean as the optical sensor) and have it trigger on the 2 raised metal pieces each side of the timing mark.
 I also want to figure out how many volts it takes to make the tack go to 7 grand. Maybe bypass all the circuitry and use a digital to analog converter ... turns number of pulses into a voltage value.

Ya, I was kinda thinking the same thing.  What would be nice is if one built a module which took the place of the inspection plug on the tranny....Im going to start to collect some info on the mag sensors, and see what I can come up with (Although I would think that you'd want the 180' apart to mimmic the coil firing ?)

[Northern RD]

I've been thinking of different ways to get a gas tach to work on a diesel.
Even went so far as to pull a tach apart and draw a schematic of the circuit.
 The gas and diesel were basically the same. Gas tach out of a '91 and a diesel tach out of an '85 turbo diesel Jetta. I figured I could probably swap a few resistors and caps and get the gas one to work with the diesel w terminal.
 This thread has been very informative. 2 pulses per revolution for the gas tach. I've also concidered using a sensor in the trany timing plug ... was thinking an optical sensor but with 2 pulses I could use a hall effect sensor (doesn't have to be kept as clean as the optical sensor) and have it trigger on the 2 raised metal pieces each side of the timing mark.
 I also want to figure out how many volts it takes to make the tack go to 7 grand. Maybe bypass all the circuitry and use a digital to analog converter ... turns number of pulses into a voltage value.

Funny you should mention the timimg plug as I had originally considered that approach. I had access to a common sensor made by Motorola that set the led and phototransistor at a 90 degree angle to each other: if the sensor could be set close enoughto the rotating flywheel the light from the led would bounce off the notch on the timing wheel to the phototransistor. The trick was building a mount for the sensor that could be adjusted to bring the sensor closer or further from, the flywheel. Some degree of adjustability seemed required.  In the end it seemed easier to do it in the manner that I described above.
N.

[SteveH]

Hrmm....Im really not a fan of any optical approach.  Granted, it would work just as well, but with clutch dust, and god-knows-what in there, I believe that magnetic sensors would be the best approach.  Affixing them would not be an issue, and dust, dirt would have no affect on performance.  I really think that we may be onto something here (as far as the timing plug goes).

-Steve

[Northern RD]

Hrmm....Im really not a fan of any optical approach.  Granted, it would work just as well, but with clutch dust, and god-knows-what in there, I believe that magnetic sensors would be the best approach.  Affixing them would not be an issue, and dust, dirt would have no affect on performance.  I really think that we may be onto something here (as far as the timing plug goes).

-Steve

Air-borne dust isn`t an issue with this sort of set-up. My trigger assy. is mounted on the outside of the lower timing cover to get it`s pulse from a small notch cut into the crank pulley. Water, dust, road trash, etc was tossed ontoit in the first 2 years of use and it functioned without a hitch. The only reason I cleaned it out after 2 years was that I thought it MIGHT need cleaning at some point.
If anything I imagine that the interior of the bell housing in the general area of the timing plug is a much more benigne environment, temperature and vibration aside.
N.

[dieselpower]

hey,
Northern RD, can you post the scematics and more detailed directions on what you did to get a tach working?

And VWRacer, I don't think the point is to "reinvent the wheel", i think it's to make it more usable. the tiny tach is a digital display witch needs some time to think and it causes a delay in the readings vs. actual rpm. I was on my dirt bike the other day and if i reved it it would be back at an idle before it showed my max rpm. witch if you ask me isnt really useful on a "preformance level".

just my 2 cents.

Mark

[VWRacer]

And VWRacer, I don't think the point is to "reinvent the wheel", i think it's to make it more usable. the tiny tach is a digital display witch needs some time to think and it causes a delay in the readings vs. actual rpm. I was on my dirt bike the other day and if i reved it it would be back at an idle before it showed my max rpm. witch if you ask me isnt really useful on a "preformance level". Mark

Quite so, but I thought the point was to have some idea of one's RPM. If it is, then the Tiny Tach is a good way to go. As I said, though, if the point is to have fun building one's own tach, then by all means go for it.

[Northern RD]

hey,
Northern RD, can you post the scematics and more detailed directions on what you did to get a tach working?

And VWRacer, I don't think the point is to "reinvent the wheel", i think it's to make it more usable. the tiny tach is a digital display witch needs some time to think and it causes a delay in the readings vs. actual rpm. I was on my dirt bike the other day and if i reved it it would be back at an idle before it showed my max rpm. witch if you ask me isnt really useful on a "preformance level".

just my 2 cents.

Mark

Sure, I BELIEVE i still have the original diagram around somewhere. Unfortunatly the car has gone to the Great autobahn in the sky so pics are out of the question.
i`ll seee what I can come up with,...
N.

[mk1vdub]

ok I have thought a bit more about this, basically my idea behind the 'tiny tach' was to use it for the piezo/transducer, just like the one that is used on the timing strobe which picks up the slight bulging of the pipe when there is an injection pulse. I would basically cuck the LCD display away and use the signal from the transducer to run a gas tacho from a gti, the signal from the transducer should be very similar to that which a gas tach recieves from the coil wire, if only a bit weaker - I can then make up the neccessary amplifying circuit to boost the signal to waht ever the gas tach would normally need to work.
the one second delay on the 'tiny tach' I am fairly sure comes from the display, as if the transucer works in the same way the timing stobe one does then it will produce a signal for every injection pulse which is what I am looking for, I am hopeing this will be an easyier way for me so I don't have to mess around with optical sensors and timing wheels etc.
I hope everyone understands my explanation, if anyone can see any problems, or offerany further advice please do.

[Northern RD]

ok I have thought a bit more about this, basically my idea behind the 'tiny tach' was to use it for the piezo/transducer, just like the one that is used on the timing strobe which picks up the slight bulging of the pipe when there is an injection pulse. I would basically cuck the LCD display away and use the signal from the transducer to run a gas tacho from a gti, the signal from the transducer should be very similar to that which a gas tach recieves from the coil wire, if only a bit weaker - I can then make up the neccessary amplifying circuit to boost the signal to waht ever the gas tach would normally need to work.
the one second delay on the 'tiny tach' I am fairly sure comes from the display, as if the transucer works in the same way the timing stobe one does then it will produce a signal for every injection pulse which is what I am looking for, I am hopeing this will be an easyier way for me so I don't have to mess around with optical sensors and timing wheels etc.
I hope everyone understands my explanation, if anyone can see any problems, or offerany further advice please do.

 Your reasoning is sound, I believe the Snap-on tach works the same way. The only issue I`d have is that piezo`s are fairly sensative and you`d have to figure out a way of using it so that it`s picking up,say, a fulse from one of the injector lines and not all the backround noise with it.
N.

[Northern RD]

You guys are

For as much effort as you are putting into just thinking and posting about this, you could build a tach that runs off the cam/injection pump sprocket. The circuitry and parts have already been figured out for you ~and~ it uses salvaged parts:
http://vwdiesel.net/phpBB/viewtopic.php?t=76
Obviously, no one has yet found a short-cut to installing an accurate tach in a diesel that's any simpler.

Technically sweet but it still has the issue that the other guys set-up has for me: taking the timing cover off, installing the pick-up sensor, etc. Too much work for someone a lazy as me   . The most complicated thing I had to fabricate was the small bracket I used for the Motorola sensor I scrounged and that was simply installed with 2 pop rivets in the timing cover. As well, the debate and ideas thrown around here IS rather intresting!!
Later,
N.
P.S.
Anybody out there guess what the "RD" stands for?

[fspGTD]

Anybody out there guess what the "RD" stands for?

Just a guess, after a clink on your profile and a quick google:
http://www.race-uscra.com/formulard.html ?

[Northern RD]

Anybody out there guess what the "RD" stands for?

Just a guess, after a clink on your profile and a quick google:
http://www.race-uscra.com/formulard.html ?

Bingo!
I have 8 of them, counting my `77 daily ride.
A pint of honey pail ale for guessing if you`re ever up this way and none for the guy who thought 'RD" indicated a location in Rohde Island,... :lol:  :lol:

[Kudagra]

HA!! Good ol SEARCH!!

SO...back on topic. Its getting to be a bit of an obsession. I KNOW there is a way.

What I cant seem to find is.. What KIND of pulse does the VW tach need. Or any tach.